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GDOT design policy manual : a Georgia Department of Transportation publication

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TABLE OF CONTENTS Chapter Revision 1. INTRODUCTION................................................................................ 6/11/2010 1.1 Purpose 1.2 Organization 1.3 Contact 1.4 Manual Updates 1.5 Project Review and Submission Requirements 1.6 Acknowledgements 2. DESIGN POLICIES, GUIDELINES, AND STANDARDS............................. 6/11/2010 2.1 General Design Policy Information 2.2 Exceptions to Design Standards 2.3 Context Sensitive Design 3. DESIGN CONTROLS.......................................................................... 4/22/2011 3.1 Functional Classification 3.2 Design Vehicles 3.3 Design Speed 3.4 Highway Capacity 3.5 Establishment of Access Control 3.6 Frontage Roads and Access Roads 3.7 Fencing 3.8 Right-of-Way Controls 3.9 Value Engineering 3.10 Environmental 4. ELEMENTS OF DESIGN....................................................................... 9/3/2010 4.1 Sight Distance 4.2 Horizontal Alignment 4.3 Vertical Alignment 4.4 Combined Horizontal and Vertical Alignments 4.5 Superelevation 5. ROADSIDE SAFETY AND LATERAL OFFSET TO OBSTRUCTIONS..........02/22/2011 5.1 General Considerations 5.2 Rural Shoulders Lateral Offset to Obstruction 5.3 Urban Shoulders Lateral Offset to Obstruction 5.4 Lateral Offsets for Signs 5.5 Lateral Offsets for Light Standards 5.6 Lateral Offsets for Utility Installations 5.7 Lateral Offsets for Signal Poles and Controller Cabinets 5.8 Lateral Offsets to Trees and Shrubs 6. CROSS SECTION ELEMENTS.............................................................07/22/2011 6.1 Lane Width 6.2 Pavement Type Selection 6.3 Cross Slope GDOT Design Policy Manual Revised 09/22/2011 Introduction 1-1 6.4 Pavement Crowns 6.5 Shoulders 6.6 Side Slopes 6.7 Border Area (urban shoulder) 6.8 Bike Lanes 6.9 Curbs 6.10 Sidewalks 6.11 Barriers 6.12 Medians 6.13 Parking Lanes 6.14 Summary of Design Criteria for Cross Section Elements 7. AT GRADE INTERSECTIONS............................................................... 6/11/2010 7.1 Intersection Design Elements 7.2 Intersection Geometrics 7.3 Median Openings 7.4 Driveways 7.5 Signalization 7.6 Highway-Railroad Grade Crossings 8. ROUNDABOUTS.................................................................................6/27/2011 8.1 Introduction 8.2 Roundabout Validation Process 8.3 Design Guidelines 8.4 References 8.5 Definition of Terms 9. BICYCLE AND PEDESTRIAN ACCOMMODATIONS............................... 3/1/2011 9.1 Overview 9.2 Typical Users & Needs 9.3 Bicycle Route Networks 9.4 Warrants for Accommodation 9.5 Facility Design 9.6 Work Zone Accessibility 10. ROADWAY USER COST UNDER DEVELOPMENT.................................. TBD 11. OTHER PROJECT TYPES.................................................................. 7/21/2011 11.1 Preventative Maintenance (PM), 3R, and Reconstruction Guidelines for Federal Aid Projects 11.2 Special Design Considerations for Other Project Types 11.3 Design Elements for Other Project Types 12. STAGE CONSTRUCTION UNDER DEVELOPMENT.................................. TBD 13. TRAFFIC FORECASTING AND ANALYSIS............................................. 5/21/2009 13.1 Traffic Forcasting Process 13.2 Freeway Traffic Analysis and Design 13.3 Arterial Traffic Analysis and Design 13.4 Trip Generation and Assignment for Traffic Impact Studies GDOT Design Policy Manual Revised 09/22/2011 Introduction 1-2 14. LIGHTING......................................................................................... 2/12/2009 14.1 General Considerations 14.2 Types of Lighting Projects 14.3 Illumination Requirements 14.4 Lighting Calculations 14.5 Design Considerations 14.6 Power Service RESOURCES Glossaries References Implementation 5/21/2007 5/21/2007 5/21/2007 GDOT Design Policy Manual Revised 09/22/2011 Introduction 1-3 1. INTRODUCTION 1.1. Purpose The GDOT Design Policy Manual is the primary resource for design guidelines and standards adopted by the Georgia Department of Transportation (GDOT) for the preparation of roadway construction plans. This manual is intended to provide guidance to the designer involving "controlling criteria" and "non-controlling criteria" recommended and in some cases stipulated by the Georgia Department of Transportation (GDOT), the American Association of State Highway and Transportation Officials (AASHTO), the Federal Highway Administration (FHWA), and various national research organizations involving the design of roadways and related infrastructure. Designers are encouraged to select design criteria that provide a balance among the design vehicle, other users of the facility, and the context of the surrounding environment. The GDOT Design Policy Manual was created by committee with representatives from GDOT, FHWA, and the consultant community in Georgia. This manual was written primarily for GDOT personnel, local governments, and consulting engineering firms that design roadway construction plans for Federal-Aid projects and State-Aid projects in accordance with the policies and objectives of Titles 23, 40, and 42 of the United States Code, and Title 32 of the Official Code of Georgia Annotated. Every effort has been made to make this manual as complete and error free as possible. 1.2. Organization The Georgia Department of Transportation improves, constructs, and maintains the state's roads and bridges and provides planning and financial support for other modes of transportation such as mass transit and airports. GDOT also provides administrative support to the State Road and Tollway Authority (SRTA) and the Georgia Regional Transportation Authority (GRTA). GDOT is managed and operated by the Commissioner of the Georgia Department of Transportation with direct oversight by the State Transportation Board. GDOT's Mission statement is: The Georgia Department of Transportation provides a safe, seamless and sustainable transportation system that supports Georgia's economy and is sensitive to its citizens and environment. The Georgia Department of Transportation Organization Chart can be found at: http://www.dot.ga.gov/aboutGeorgiadot/Documents/OrgChart.pdf The GDOT Division of Engineering has the primary role in the roadway design process. The mission of the Division of Engineering is to develop a quality set of right of way plans, construction plans, and bid documents, through a cooperative effort, that results in a project design and implementation that is the best transportation value for the taxpayers of Georgia. Offices under the umbrella of the Division of Engineering are: 1. Office of Environmental Services 2. Office of Design Policy & Support Design Policy/Standards/Hydraulic Engineering and ESPCP Tech Support Statewide Location Bureau Engineering Systems Support 3. Office of Roadway Design 4. Office of Bridge and Structural Design 5. Office of Right-of-Way GDOT Design Policy Manual Revised 06/11/2010 Introduction 1-1 1.3. Contact The GDOT Design Policy Manual is maintained by the Office of Design Policy & Support. To submit questions or comments specific to the GDOT Design Policy Manual and its contents, please send an e-mail to: [email protected] The current GDOT Design Policy Manual is published on the Department's Repository for Online Access to Documentation and Standards (R.O.A.D.S) homepage at: http://www.dot.ga.gov/doingbusiness/PoliciesManuals/roads/Pages/default.aspx 1.4. Manual Updates The GDOT Design Policy Manual will be periodically updated so that it appropriately reflects the Department's current design policies and practices. An entire chapter or any portion of one or more chapters of the manual may be re-written and replaced at any time. Revisions to this manual are summarized in the Table of Contents. The version and latest revision date are listed in the manual's Table of Contents, in the Table of Contents for each chapter, and at the bottom of each page of the manual. Implementation dates may be specified for certain revisions. Subscribers to the R.O.A.D.S. homepage will receive e-mail notices of updates to the GDOT Design Policy Manual. 1.5. Project Review and Submission Requirements Project review and submission requirements shall be in accordance with the latest edition of the GDOT Plan Development Process (PDP). The current PDP is published online at: http://www.dot.ga.gov/doingbusiness/PoliciesManuals/roads/Pages/default.aspx The GDOT PDP sets forth the current procedures and steps necessary for GDOT to administer Federal-Aid projects in accordance with the policies and objectives of Titles 23, 40, and 42 United States Code, and to administer State-Aid projects to fulfill the policies and objectives of Title 32, Official Code of Georgia Annotated. The GDOT PDP outlines the current process of project development from project identification through construction award. All design criteria and design decisions should be documented in a Project Design Data Book, which is to be included with the project files. Procedures and criteria for the Project Design Data Book are provided in the GDOT PDP Chapter 6, Preliminary Design. 1.6. Acknowledgements The Georgia Department of Transportation Division of Engineering wishes to acknowledge the following for their contribution to the development of the GDOT Design Policy Manual: GDOT - Brent Story, Eugene Hopkins, Brad Ehrman, Kim Fulbright, Ben Buchan, Darrell Richardson, Darryl Van Meter, Chuck Hasty, Babs Abubakari, Keith Golden, Kathy Bailey, Abby Ebodaghe, Gary Langford, Joel North, Joe Wheeler, Ron Wishon, Del Clippard FHWA - David Painter and the Georgia Division of FHWA Consultants - Stan Hicks, Bill Pate, Jody Braswell, Jill Hodges, Joe Macrina, Tim Heilmeier, Taylor Stukes, Julie Doyle, Jeff Dyer, Michael Holt, Mike Reynolds, Harris Robinson, Vern Wilburn GDOT Design Policy Manual Revised 06/11/2010 Introduction 1-2 Chapter 2 Contents 2. Design Policies, Guidelines, and Standards 1 2.1. General Design Policy Information 1 2.1.1. Sources of Design Policy and Practice 2 2.2. Exceptions to Design Standards 4 2.2.1. Design Exception 4 2.2.2. Design Variance 4 2.3. Context Sensitive Design 5 Chapter 2 Index 6 GDOT Design Policy Manual Revised 6/11/2010 Chapter 2 Contents i 2. DESIGN POLICIES, GUIDELINES, AND STANDARDS 2.1. General Design Policy Information Design policy is defined as the basic principles and goals established by GDOT to guide (guidelines) and control (standards) the design of roadways and related infrastructure in Georgia. The intent of design policy is to provide recommended and stipulated values for critical dimensions. Flexibility is permitted to encourage independent design tailored to individual situations. When flexibility is applied to a proposed design, and critical dimensions do not meet GDOT design policy, additional documentation is required to record the decision-making-process. Criteria within this manual denoted as "standard" or as "controlling criteria" have been identified as a required or mandatory practice with deviation from the controls requiring prior agency approval. All other criteria within this manual are considered to be "non-controlling criteria" and are denoted as "guidelines" intended as recommended practice with deviation allowed if engineering judgment or study indicate the deviation to be appropriate. Designers are encouraged to select design criteria that provide a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. Unless stated otherwise, the policies in this manual apply to permanent construction of roadways and related infrastructure. Different criteria may be applicable to temporary facilities. Guidance specific to non-interstate roadway resurfacing, restoration, or rehabilitation (3R) projects is provided in Chapter 11 of this Manual. The following definitions offer guidance for interpreting policy statements found in this manual: Standard a required criteria or mandatory practice. Criteria denoted as standard have been identified by the Department as having substantial importance to the operational and safety performance of a roadway such that special agency review and approval (Design Variance or Design Exception) will be required before deviation from the controls can be incorporated into a design. All controlling criteria are denoted as standard. In some cases, GDOT has denoted specific non-controlling criteria as standard. Controlling Criteria: The FHWA has specifically identified "13 controlling criteria" (listed below) as having substantial importance to the operational and safety performance of a roadway such that special agency attention should be given to the criteria in the design decision making process. 1. Design speed 2. Lane width 3. Shoulder width 4. Bridge width 5. Horizontal alignment 6. Superelevation 7. Vertical alignment 8. Grades 9. Stopping sight distance 10. Cross slope 11. Vertical clearance 12. Lateral offset to obstruction 13. Structural capacity The conditions of the "13 controlling criteria" are defined by AASHTO and are adopted and denoted as standard criteria by GDOT. In some cases, GDOT provides more specific and selective guidelines relating to controlling criteria; however, at a minimum, the conditions defined by AASHTO control. A decision to use a design value that does not meet the minimum controlling criteria defined by AASHTO will require the prior approval of a Design Exception from the GDOT Chief Engineer. GDOT Design Policy Manual Revised 6/11/2010 Design Policies, Guidelines, and Standards 2-1 Shall: The use of the word "shall" denotes a required or mandatory condition, and the designer must make every effort to follow the appropriate design criteria or condition. Guideline recommended practice in typical situations. Deviations from criteria denoted as guidelines are allowed when engineering judgment or study indicates the deviation to be appropriate. Adequate study, justification, and documentation by the GDOT office or consultant responsible for the engineering is required. Decisions to deviate from guidelines are subject to review and scrutiny by GDOT at any time. Should: The use of the word "should" indicates an advisory condition. Under this condition, it is recommended, although not mandatory, that the designer follow the appropriate design criteria. May: The use of the word "may" indicates a permissive condition. Under this condition, the designer is encouraged to use sound engineering judgment. Practical: The use of the word "practical" is intended to indicate that a design decision is effective and applicable with consideration to economic resources; appropriate, adaptable, and balanced. Where practical: The use of the term "where practical" is intended to indicate that agencies may consider economic resource constraints when making a decision. 2.1.1. Sources of Design Policy and Practice GDOT adopts the AASHTO Green Book, "A Policy on Geometric Design of Highways and Streets," and the AASHTO "A Policy on Design Standards for the Interstate System" as the standard for controlling criteria required and mandatory on State Routes and routes on the National Highway System (NHS) in Georgia. For additional guidance on the design of roadways and related infrastructure, refer to the most current edition of the following publications, unless a specific version is noted. These publications, including the website addresses (url) for resources available online, are cited in the References section of this Manual: American Association of State Highway and Transportation Officials (AASHTO) A Policy on Geometric Design of Highways and Streets (Green Book) A Policy on Design Standards---Interstate System Guide for the Development of Bicycle Facilities Guide for High-Occupancy Vehicle (HOV) Facilities Guide for Park-and-Ride Facilities Guide Specifications for Horizontally Curved Steel Girder Highway Bridges Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT 400) Highway-Rail Crossing Elimination and Consolidation Roadside Design Guide Roadway Lighting Design Guide Standard Specifications for Highway Bridges American Railway Engineering and Maintenance of Way Association (AREMA) Manual for Railway Engineering Federal Highway Administration (FHWA) Americans with Disabilities Act (ADA) and Transportation Enhancements (TE) GDOT Design Policy Manual Revised 6/11/2010 Design Policies, Guidelines, and Standards 2-2 Flexibility in Highway Design Guidance on Traffic Control Devices at Highway-Rail Grade Crossings Highway-Railroad Grade Crossings: A Guide to Consolidation and Closure Manual on Uniform Traffic Control Devices (MUTCD) Roundabouts: An Informational Guide FHWA-RD-00-67 Value Engineering and The Federal Highway Administration (Website) Roadway Lighting Handbook Mitigation Strategies for Design Exceptions Georgia Department of Transportation (GDOT) Bridge and Structures Policy Manual Environmental Procedures Manual Manual on Drainage Design for Highways Construction Standards and Details Context Sensitive Design Online Manual Pavement Design Manual Pedestrian and Streetscape Guide Plan Development Process (PDP) Plan Presentation Guide Regulations for Driveway and Encroachment Control Standard Specification Book Traffic Analysis and Design Manual Traffic Signal Design Guidelines Utility Accommodation Policy and Standards Manual Georgia Soil and Water Conservation Commission (GSWCC) Manual for Erosion and Sediment Control in Georgia Illuminating Engineering Society of North America (IESNA) Guideline for Security Lighting for People, Property and Public Spaces Lighting Handbook, 9th Edition Lighting For Parking Facilities Recommended Lighting for Walkways Recommended Lighting for Walkways and Class 1 Bikeways Roadway Lighting ANSI Approved Roadway Sign Lighting Tunnel Lighting Roundabout Lighting Institute of Transportation Engineers (ITE) GDOT Design Policy Manual Revised 6/11/2010 Design Policies, Guidelines, and Standards 2-3 Manual of Uniform Transportation Engineering Studies Trip Generation Handbook National Cooperative Highway Research Program (NCHRP) Modern Roundabout Practices [Synthesis 264] Design Speed, Operating Speed, and Posted Speed Practices [NCHRP Report 504] Evaluating Intersection Improvements: An Engineering Study Guide [NCHRP Report 457] Impacts of Access Management Techniques [NCHRP Project 3-52] Recommended Procedures for the Safety Performance Evaluation of Highway Features [Report 350] National Fire Protection Association (NFPA) National Electrical Code [NFPA-70] Texas Transportation Institute (TTI) Grade Separations - When Do We Separate? Highway-Rail Crossing Conference Transportation Research Board (TRB) Highway Capacity Manual 2.2. Exceptions to Design Standards 2.2.1. Design Exception If a design feature of a new construction or reconstruction project does not meet the minimum conditions of one of the "13 controlling criteria" defined in the current edition of the AASHTO Green Book and the AASHTO publication, A Policy on Design Standards - Interstate System, then approval to build or retain the feature is required by formal Design Exception. For projects identified as "Full Oversight" such as interstate projects, the FHWA is the agency that grants Design Exceptions. For all other projects, both federally and state funded, the GDOT Chief Engineer grants Design Exceptions. The requirement of a Design Exception is not meant to impede design flexibility, but to document a very important design decision that is well scrutinized by the Department in a deliberative and thorough manner. To obtain a Design Exception, a comprehensive study and formal request shall be submitted using the format and procedures outlined in the GDOT Plan Development Process (PDP), and in the FHWA publication, Mitigation Strategies for Design Exceptions. 2.2.2. Design Variance Whenever a "non-controlling" criteria has been denoted by GDOT as a standard, then the approval of a Design Variance must be obtained by the GDOT Chief Engineer before deviation outside the controls can be incorporated into the design. The requirement of a Design Variance is not meant to impede design flexibility, but to document a very important design decision that is well scrutinized by the Department in a deliberative and thorough manner. To obtain a Design Variance, a comprehensive study and formal request shall be submitted using the format and procedures outlined in the GDOT Plan Development Process (PDP). GDOT Design Policy Manual Revised 6/11/2010 Design Policies, Guidelines, and Standards 2-4 2.3. Context Sensitive Design Context Sensitive Design (CSD) is a process for achieving design excellence by developing transportation solutions that require continuous, collaborative communication and consensus among transportation agencies, professionals, and stakeholders. A common goal of CSD projects is to develop a facility that is harmonious with the community, and preserves aesthetics, history and the environmental resources, while integrating these innovative approaches with traditional transportation goals for safety and performance. Refer to the GDOT Context Sensitive Design Online Manual for additional information on communication strategies, design flexibility, environmental sensitivity, and stakeholder involvement for developing successful context-sensitive solutions. GDOT Design Policy Manual Revised 6/11/2010 Design Policies, Guidelines, and Standards 2-5 Chapter 3 Contents 3. Design Controls 3.1. Functional Classification 3.2. Design Vehicles 3.2.1. Design Vehicle Types 3.2.2. Local Input for Selecting a Design Vehicle 3.3. Design Speed 3.3.1. 3.3.2. 3.3.3. 3.3.4. General Considerations Intersections Approaching a Stopped Condition Freeway Exit and Entrance Ramps Urban Subdivision Streets 3.4. Highway Capacity 3.5. Establishment of Access Control 3.5.1. Definitions 3.5.2. Access Management 3.6. Frontage Roads and Access Roads 3.7. Fencing 3.7.1 Fencing on State Right-of-Way 3.7.2 Fencing on Private Property 3.8. Right-of-Way Controls 3.8.1. 3.8.2. 3.8.3. 3.8.4. Rural Areas Urban Areas Special Types of Right-of-Way Accommodating Utilities 3.9. Value Engineering 3.10. Environmental Chapter 3 Index List of Figures Figure 3.1 Limit of Access Control Interstate/Freeway Interchange List of Tables Table 3.1 Minimum Design Vehicles GDOT Design Policy Manual Revised 4/22/2011 Chapter 3 Contents 1 1 5 5 6 7 7 7 7 8 8 8 8 9 11 12 12 13 14 14 15 15 15 16 16 18 10 5 i 3. DESIGN CONTROLS This chapter provides information with regard to design controls. Many factors contribute to the roadway design criteria used by designers. These factors are based upon the physical characteristics of the vehicles (vehicle types), the topography in which the road is set, operational safety and speed of traffic on the road, and even driver behavior (speed, turns, following distance, clear zones for emergencies). All of these factors are important and should be balanced when selecting the appropriate design criteria for a particular road or highway design. This chapter addresses: functional classification; design vehicles; design speed; highway capacity and level of service; access control; frontage and access roads; fencing; right-of-way controls; value engineering; and environmental considerations. 3.1. Functional Classification Design standards have been developed by the American Association of State Highway and Transportation Officials (AASHTO) for different functional systems of roadways. In order to qualify for federal funding, the Federal Highway Administration (FHWA) requires that each state categorize state routes by functional classification. Detailed discussions on the concept of functional classification and the characteristics of the various functional systems can be found in the AASHTO Green Book1 and FHWA Functional Classification Guidelines2,3. Additional information specific to GDOT policies related to functional classification of roadways is also available in the GDOT Plan Development Process (PDP). Roadway functional classification serves as the foundation of an access management program. Functional classification systems establish the planned function of different types of roadways and the priority placed on access as opposed to through traffic movement. Functional classification recognizes that design considerations vary for different classes of roads in accordance with the intended use. 1 AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book). 2 FHWA. FHWA Functional Classification Guidelines. 1989 Note: The 1989 version of this publication is available online at http://www.fhwa.dot.gov/planning/fctoc.htm 3 FHWA, FHWA 2008 Updated Guidance for the Functional Classification of Highways, Memorandum from Mary B. Phillips, Associate Administrator for Policy and Governmental Affairs dated October 14, 2008. GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-1 Streets and highways are grouped into major classes based on the type or kind of service they provide. The functional classification process is based on the fact that roads are part of a travel network and that "individual roads and streets do not serve travel independently in any major way" (Functional Classification Guidelines, 1989). The three major functional systems are: Freeways; Arterials; and collectors and local streets. Freeway Classification Freeways can be distinguished from all other roadway systems in that they provide uninterrupted flow. There are no fixed interruptions on freeways. The traffic flow conditions along uninterruptedflow facilities result primarily from the interactions among vehicles in the traffic stream and between vehicles and the geometric and environmental components of the roadway. Access to the freeway facility is controlled and limited to ramp locations, whereas access to an interrupted flow facility uses at-grade intersections. Categorization of uninterrupted and interrupted flow relates to the type of facility as opposed to the quality of the traffic flow at any given time. A freeway experiencing extreme congestion differs greatly from a non-freeway facility experiencing extreme congestion, in that the conditions creating the congestion are commonly internal to the facility, not external to the facility. Freeway facilities may have interactions with other freeway facilities as well as other classes of roads in the vicinity. The performance of a freeway may be affected when demand exceeds capacity on these nearby road systems. For example, if the street system cannot accommodate the demand exiting the freeway, over-saturation of the street system may result in queues backing onto the freeway, which adversely affects freeway performance. Traffic analysts and designers must also recognize that freeway systems have several interacting components, including ramps, and weaving sections. To achieve an effective overall design, the performance of each component must be evaluated separately and the interactions between components must also be considered. For example, the presence of ramp metering affects freeway demand and must be taken into consideration when analyzing a freeway facility. Arterial Classification Arterials are a functional classification of roadway transportation facilities that are intended to provide for through trips that are generally longer than trips on collector facilities and local streets. While the need to provide access to abutting land is not the primary function, the design of arterials must also balance this important need. To further highlight the often competing demands of urban arterials, other modes of travel such as pedestrians and public transit are also present and must be accommodated. To assure that an arterial can safely provide an acceptable level of service (LOS) for the design conditions, a number of design elements must be addressed. Since each design element is essentially determined based on separate analyses, the designer should evaluate the entire arterial system and be prepared to refine certain elements to obtain an effective and efficient overall design. GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-2 Arterial systems are often further sub-classified into Principal or Minor arterial functional systems based on the trips served, the areas served, and the operational characteristics of the streets or highways. "Since urban and rural areas have fundamental different characteristics with regards to the density of land use, nature of travel patterns and the number of streets and highway network and the way in which these elements are related, urban and rural functional systems are classified separately as urban principal and minor arterials and rural principal and minor arterials" (FHWA. 1989). These functional systems are therefore discussed individually under the Urban Arterial Classification and Rural Arterial Classification sections below. Urban Arterial Classification The AASHTO Green Book defines urban areas as those places within the boundaries set by the responsible State and local officials having a population of 5,000 or more. Urban areas are further subdivided into urbanized areas (population of 50,000 and over) and small urban areas (population between 5000 and 50,000) (AASHTO). For design purposes, the designer should use the population forecast for the design year. There are four functional systems for urban areas: Urban Principal Arterials - almost all fully and partially controlled access facilities in urban areas are considered urban principal arterials; however, this system is not restricted to controlled access routes. FHWA further stratifies the principal arterial system as: interstate, other freeways and expressways, and other principal arterials with no control of access (Functional Classification Guidelines, 1989). Urban Minor Arterials - includes all arterials not classified as a principal. This functional system includes facilities that: o place greater emphasis on land access than principal arterials and offer a lower level of traffic mobility; o interconnect with, and augment, the urban principal arterial system; o provide service to trips of moderate length at a somewhat lower level of travel mobility than principal arterials; o distribute travel to smaller areas than those of urban principal arterials; and o may carry local bus routes and provide intra-community continuity, but ideally should not penetrate identifiable neighborhoods. Note: this system should also include urban connections to rural collector roads where such connections have not been classified as urban principal arterials. (AASHTO Green Book) Collector Streets Some characteristics of collector streets are that they: o provide access and traffic circulation within residential neighborhoods, commercial, and industrial areas; o may penetrate residential neighborhoods, distributing trips from the arterials to destinations; and GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-3 o collect traffic from local streets in residential neighborhoods and channel traffic to the arterial system. (AASHTO Green Book) Local Streets - Some characteristics of local streets are that: o local streets provide direct access to abutting land and access to higher systems; and o local street systems offer the lowest level of mobility and usually contain no bus routes. Service to through traffic movement in this system is usually deliberately discouraged. (AASHTO Green Book) Rural Arterial Classification The functional systems for urban arterials and rural arterials differ due to factors such as intensity and type of development that occurs on these systems. Rural Principal Arterials almost all fully and partially controlled access facilities in rural areas are considered rural principal arterials; however, this system is not restricted to controlled access routes. Service characteristics of rural principal arterials include: o traffic movements with trip length and density suitable for substantial statewide travel or interstate travel; o traffic movements between urban areas with populations greater than 25,000; o traffic movements at high speeds; o divided four-lane roads; and o desired LOS B. Rural Minor Arterials have the following service characteristics: o traffic movements with trip length and density suitable for integrated interstate or inter-county service; o traffic movements between urban areas or other traffic generators with populations less than 25,000; o traffic movements at high speeds; o undivided lane roads; o striped for one or two lanes in each direction with auxiliary lanes at intersections as required by traffic volumes; and o desired LOS B. ( AASHTO Green Book) Refer to the AASHTO Green Book, Chapter 1. Highway Functions, for additional information regarding functional classification. Mapping of roadway functional classifications for all urban and non-urban areas in Georgia is maintained by the GDOT Office of Transportation Data. Functional Classification Maps for Georgia State roadways may be downloaded from GDOT's website at: http://www.dot.ga.gov/maps/Pages/HighwaySystem.aspx. GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-4 3.2. Design Vehicles In the design of any roadway facility, the designer should consider the largest design vehicle that is likely to use that facility with considerable frequency or a design vehicle with special characteristics appropriate to a particular location in selecting design vehicles. 3.2.1. Design Vehicle Types The four general classes of design vehicles as defined by AASHTO are: Passenger Cars - Passenger automobiles of all sizes, including cars, sport/utility vehicles, minivans, vans, and pick-up trucks; Buses - Intercity (motor coaches), city transit, school, and articulated buses; Trucks - Single-unit trucks, truck tractor-semi-trailer combinations, and truck tractors with semi-trailers in combination with full trailers; and Recreational Vehicles - Motor homes (including those with boat trailers and pulling an automobile), automobiles pulling a camper trailer or a boat trailer. Table 3.1 Minimum Design Vehicles Roadway Type Rural Minimum Design Vehicle Typical Design Speed (mph) Interstate / Freeway Ramp Free-Flow Entrance / Exit Loop Primary Arterial Minor Arterial Collector Local Road WB-67 70 WB-67 WB-67 WB-67 WB-40 or WB-62 SU SU 35 (minimum)(2) 35 (minimum)(2) 35 (minimum)(2) 65 65 55 Paved S-BUS36 45 Gravel Urban S-BUS36 35 Refer to the current AASHTO Green Book Chapter 2, Design Controls and Criteria, for further discussion on use of design vehicles and for detailed dimensions of design vehicles. Table 3.1. lists minimum vehicles which should be considered when selecting an appropriate design vehicle. Design vehicle dimensions are defined in the AASHTO Green Book (2004), Exhibit 2-1. Design Vehicle Dimensions. Interstate / Freeway Ramp Terminal Ramp Free-Flow Entrance / Exit Loop Primary Arterial Minor Arterial Collector Residential/Local Road WB-50 65 WB-67 WB-67 WB-40 or WB-62 WB-40 or WB-62 WB-40 or BUS-40 BUS-40 or SU 35 (minimum)(1) 35 (minimum)(1) 35 (minimum)(1) 55 45 35 SU or P 35 Turning Radii The minimum turning path of the selected design vehicle is the primary factor in (1) Refer to Section 3.3.3 Freeway Ramps. Design Vehicle Type Symbols: BUS=Intercity Bus/Motor Coach, P=Passenger Car, S-BUS=School Bus, SU=Single-Unit Truck, WB=Semi Trailer designing radii at intersections, radii of turning roadways, median opening geometry and commercial driveways. The turning radii can affect the cross-section width of a roadway. In other words, the larger the required turning radii to accommodate larger design vehicles, the wider the roadway cross-section needs to be. For GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-5 example, a semi-trailer truck would need a much larger turning radii at a median opening to properly access a business or commercial distribution center than a passenger car or van. Design tools that can be used to determine the turning path for a given design vehicle include: Published templates which show the wheel paths of a design vehicle, such as the AASHTO Green Book, Exhibits 2-3 through 2-23, which presents the minimum turning path for 19 typical design vehicles; and Vehicle turn simulation software, such as AutoTURN3, which works within both MicroStation and AutoCAD. The need to provide turning radii for larger vehicles may sometimes conflict with the need to accommodate pedestrians. The design of an intersection should not prohibit safe pedestrian movements through the intersection. Refer to the GDOT Pedestrian and Streetscape Guide4 for information specific to accommodating pedestrians. Further discussion of GDOT policies relating to intersection design can be found in this Manual in Chapter 7, At-Grade Intersections and Chapter 8, Roundabouts. 3.2.2. Local Input for Selecting a Design Vehicle The designer should be aware of all potential types of vehicles that will use each part of the facility and larger vehicles should be accommodated, where practical. Input from local personnel should be considered by the designer when determining the proper design vehicle for each local road that intersects the project. Local personnel may include the GDOT Area Engineer, Maintenance Engineer, District Access Engineer, or local government personnel. This determination should be completed during the conceptual design phase. Scenarios where solicitation of local government input is recommended include: areas where bicycle use is allowed on a roadway - in which case the bicycle should be considered a design vehicle; roadways leading to recreational areas like state parks, campgrounds, and marinas - in which case recreational vehicles, such as motor homes or pick-up trucks with boat trailers, may be the appropriate design vehicle; some areas near timber processing facilities - in which case, "long log" trucks (trucks with logs overhanging the trailer by as much as 12-ft.) may be prevalent, as intersections in these areas may require a design that prevents overhanging logs from striking vehicles in other lanes during turning movements. This can usually be accomplished by physically separating the turning lane from adjacent through lanes; and school bus routes. 3 AutoTURN is developed by Transoft Solutions. Additional information about this software application is available online at: http://www.transoftsolutions.com/ProductTmpl.aspx 4 GDOT/Otak. Pedestrian and Streetscape Guide. 2003 The 2003 version of this publication is available online at: http://www.dot.ga.gov/travelingingeorgia/bikepedestrian/Pages/PlanningandDesignResources.aspx GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-6 3.3. Design Speed 3.3.1. General Considerations "Design Speed" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for design speed options for roadway classifications in Georgia. The designer is encouraged to select a design speed that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a design speed value that does not meet the controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer. Design speed is different from other controlling criteria in that it is a design control, rather than a specific design element. In other words, the selected design speed is used to establish a range of design values for many of the geometric elements of a roadway. The selected design speed should be a logical one with respect to the topography, anticipated operating speed, the adjacent land use and functional classification of the roadway. Design speed should be consistent with the speeds at which 85 percent of drivers are traveling (referred to as the 85th percentile) and likely to expect on the facility. In recognition of the wide range of site-specific conditions, constraints, and contexts for roadways AASHTO defines a range of values for design speed. A design speed that is as high as practical that will provide safety, mobility, and efficiency within the constraints of environmental quality, economics, aesthetics, and other social or political effects should be selected. Table 3.1. lists typical design speeds which should be considered when selecting an appropriate design speed. On county roads or city streets, GDOT recommends coordination with the local jurisdictional authority to identify posted speeds on existing roadways and for the selection of the posted speed limit and the design speed for new or reconstructed roadways. 3.3.2. Intersections Approaching a Stopped Condition To improve the angle of intersection between a local street and major road, a designer may use a lower design speed on the local street for curves approaching an intersection if it is not anticipated that the T-intersection will become a full intersection. The design speed of the last curve prior to the intersection may be 10 mph less than the design speed of the local street. 3.3.3. Freeway Exit and Entrance Ramps Typical freeway exit and entrance ramps may have varying design speeds which are based on the operating speed of the vehicle as it decelerates or accelerates on the ramp. A common rule to apply for ramps is that the design speed of the first curve of an exit ramp can be assumed to be 10 mph less than the design speed of the mainline. With each successive curve on the exit ramp, the design speed of the curve can be reduced based on computed vehicle deceleration. The reverse condition applies to the design speed for all entrance ramps. The design speed for a direct system to system ramp that connects two freeway facilities should be no less than 10 mph below the design speed of the exiting facility. GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-7 On loop ramps, adequate deceleration length should be provided prior to the loop part of the ramp. All areas of deceleration should be separated from the mainline lanes. System to system loop ramps will be evaluated on a case-by-case basis. 3.3.4. Urban Subdivision Streets In most cases, the design speed for urban subdivision streets should be a minimum of 25 mph. 3.4. Highway Capacity All portions of roadways that are part of major construction or reconstruction should be designed to accommodate, at a minimum, 20-year forecasted traffic volumes. The design year for the 20-year traffic volumes should be forecasted from the estimated base (or opening) year, which is the year the project is anticipated to be open for traffic use. Refer to Chapter 13, Traffic Forecasting and Analysis Concepts, of this Manual for further discussion on the traffic engineering and analysis. If a project is not new roadway construction or reconstruction, refer to Chapter 11, Other Project Types for guidance relating to other project types. 3.5. Establishment of Access Control 3.5.1. Definitions GDOT has adopted the following "Access Control" criteria as standard, having substantial importance to the operational and safety performance of a roadway such that special attention should be given to design decisions. The designer is encouraged to select design elements and features that are consistent with the access control plan established for a roadway. A decision to use a design element or feature that does not meet the standard access control criteria defined by GDOT shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the Department's Chief Engineer. Roadways serving higher volumes of regional through traffic require greater access control to preserve their traffic function. Frequent and direct property access is more compatible with the function of local and collector roadways. The regulation of access to a roadway is referred to as "access control". It is achieved through the regulation of public access rights to and from properties abutting the roadway facilities. The Official Code of Georgia Annotated (OCGA)5 32-6-111 to 114 give GDOT this authority. The regulation of public access rights is generally categorized as either full control of access, partial control of access, or control of access by permit (or permitted access). Full control of access means that preference is given to through traffic by providing access connections by means of ramps with only selected public roads and by prohibiting crossings at grade and direct driveway connections. Partial control of access means that some preference should be given to through traffic. Access connections, which may be at-grade or grade-separated, are provided with selected public roads 5 Online public access to the Official Code of Georgia Annotated (OCGA) is provided at: http://w3.lexis-nexis.com/hottopics/gacode/Default.asp?loggedIn=done GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-8 and private driveways. In areas with partial control of access, the decision to grant access to private driveways is made at the time of project development, and thereafter, private driveway access should not be added. Permitted access means that a permit is needed for access. A permit is required prior to performing any construction work or non-routine maintenance within the State highway right-of-way. This includes but is not limited to the following activities: grading, landscaping, drainage work, temporary access to undeveloped land for logging operations, or construction of a development. Any new driveway or revisions to any portion of existing driveways, i.e. widening and/or relocation that are within the State roadway right-of-way shall also require a permit. 3.5.2. Access Management The following standards shall be used to establish access control: Full control of access Full control of access shall be established on all Interstates. Full control of access shall be established on principal arterials constructed on new location with grade separated interchanges. For projects that involve an Interstate interchange, (new construction or reconstruction), access control should be established along the intersecting route for a distance of 600-ft. in urban areas and 1,000-ft. in rural areas, where practical. At a minimum, access control shall not be less than 300-ft. This distance is measured from the radius return of the ramp termini with the intersecting route. (See Figure 3.1, Limit of Access Control Interstate/Freeway Interchange). Where improved traffic operations and safety warrant, existing driveways may be closed and no access allowed to developed or undeveloped property. Decisions on elimination of access points should be based in part on an economic study of alternate courses of action. Partial control of access Partial control of access shall be established on principal and minor arterials that are constructed on a new location with intersections at-grade. Access control should not be established on portions of projects on new location which are less than one mile in length, unless the project connects to a section of roadway were access control has been or will be established or where required to preserve the functional area of an intersection as described below. Partial control of access should be established on existing principal arterials that are being widened, when it is determined that partial access control is advisable. On this type of project, every attempt shall be made to consolidate existing access to the roadway by developing a supporting roadway network. All undeveloped property frontage should be treated in the same manner as new location construction. Breaks in access will only be granted for the following conditions: State or local government public road intersections GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-9 GDOT Design Policy Manual Revised 4/22/2011 Figure 3.1 Limit of Access Control Interstate/Freeway Interchange Design Controls 3-10 Where property that is not accessible from existing roadways or has been bisected by the new roadway alignment and no other access is provided and the appraised damages to the remaining property exceeds $50,000 in a rural area or $100,000 in an urban area. Coordination with the District right-of-way office should be performed prior to making a request for a break in access control. All breaks in access control under these conditions must be approved by the Chief Engineer. Permitted access On principal and minor arterials and major collector roadways that are being reconstructed, access rights should be acquired so that driveway connections are not allowed within the functional area of any intersection. The functional area of an intersection is the area where motorists are responding to the intersection, decelerating, and maneuvering into the appropriate lane to stop or complete a turn. Access connections too close to intersections can cause serious traffic conflicts that impair the function of the affected facility. Upstream functional distance is defined as the distance traveled during perception-reaction time, plus the deceleration distance while the driver maneuvers to a stop, plus the queue storage. Downstream functional distance is defined as the stopping sight distance. Temporary State Routes For routes that are temporarily placed on the state route system during project development, close coordination to determine the appropriate access control should occur between the Department and the local government responsible for enforcing the access control after the oversight reverts back to the local government. "Permitted Access" should be considered when there is a strong likelihood that access breaks will be requested by potential development along the route. "Full Control of Access" or "Partial Control of Access" should be considered when the project connects to a section of roadway where similar access control has been or will be established, and to preserve the functional classification of the route or corridor. Before Right of Way acquisition begins, it is recommended that the Department receive written confirmation from the local government to enforce the established access control after the oversight reverts back to the local government. 3.6. Frontage Roads and Access Roads AASHTO defines a frontage road as "a road that segregates local traffic from higher speed throughtraffic and intercepts driveways of residences, commercial establishments, and other individual properties along the highway" (AASHTO Green Book). Frontage roads can serve many functions depending on the type of arterial they serve and the character of the surrounding area. They are commonly used to control access to the arterial, to provide access to adjoining properties, and to maintain traffic circulation on each side of the arterial. Most existing frontage roads were built along interstate or major arterial routes to control access to these routes and provide access to property that would otherwise be land-locked. Access roads may also be used to provide access to landlocked parcels. Frontage roads typically run parallel to the mainline route while access roads provide access to individual properties and may not run parallel to the mainline. Access roads and frontage roads should be offset from the mainline route to allow required clear zone and future roadway widening, if anticipated. GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-11 3.7. Fencing The Georgia Department of Transportation has established the following guidelines for installing fence on state right-of-way and/or private property associated with the design of roadway projects. These guidelines are based on the principles published in the AASHTO An Informational Guide on Fencing Controlled Access Highways (1990). 3.7.1 Fencing on State Right-of-Way Fencing is provided within the state right-of-way to delineate the boundary of the acquired access control, and as a physical obstacle to deter encroachment onto the roadway right-of-way from children, pedestrians, bicyclist, vehicles, machinery, and animals. Fencing may also be provided to deter access into or across specific features within the right-of-way such as drainage structures, bridges and retaining walls. The following guidelines are provided for the consistent application of fencing on state right-of-way. Roadways with Full Control of Access are expected to provide a higher level of mobility and operate at higher speeds with protection from all forms of roadside interference. Therefore, fencing should be installed within the state right-of-way on roadways with Full Control of Access, where it is practical to do so. Fencing may not be practical or necessary in areas with steep slopes or natural barriers. Fencing may be installed within the state right-of-way on roadways with Partial Control of Access or any portion of a state route with an acquired limit-of-access if the Department determines it necessary to deter potential or chronic encroachment. For roadways with Full Control of Access and parallel frontage roads included within the state right-of-way, fencing should be installed between the mainline traveled-way and the frontage road. In these cases, it may not be necessary to install a duplicate fence along the right-of-way line. Fence installed within the state right-of-way to delineate the limit-of-access should be offset a minimum of 1-ft inside the right-of-way line to ensure there is adequate space for installation and maintenance. For non-access grade separations, fence installed along the limit-of-access will be terminated at the points where the state right-of-way intersects the normal right-of-way of the crossing grade separation. For grade separated interchanges, fence installed along an entrance or exit ramp terminal with a cross road should terminate at the point where the state right-of-way intersects the normal right-of-way along the cross road. Fencing may be extended along the right-of-way of the cross road for the entire length of acquired access control if the Department determines it necessary to deter potential or chronic encroachment (see Figure 3.1, Limit of Access Control Interstate/Freeway Interchange. Fence installations within the state right-of-way are not intended to control livestock from adjacent private property and should not be installed or permitted for this reason. Where fencing is required to contain livestock within adjacent private property, an independent fence on private property will be required for that purpose (see 3.7.2. Fencing on Private Property). The installation of 6-ft height Chain Link Wire Fence should be considered on a case-bycase-basis around the perimeter of proposed permanent drainage features that will contain GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-12 water over 24-inches deep for an extended period of time (greater than 48 hours). For example, natural ponds, detention ponds and water quality ponds within the state right-ofway. The fence should be installed with adequate space for routine maintenance and equipped with self-closing and self latching gates. A fence or handrail should be considered on a case-by-case-basis along the top of a retaining wall with a change in elevation of 30-inches or more above the grade below. These cases should be assessed independent of fencing along a limit-of-access. For guidance on the design and installation of fence or handrail on bridges, refer to Chapter 3.4.1.2 of the GDOT Bridge and Structures Design Policy Manual. http://www.dot.ga.gov/doingbusiness/PoliciesManuals/roads/BridgeandStructure/GDOT_Bridge_and_Structur es_Policy_Manual.pdf For guidance on the construction of fencing, refer to GDOT Construction, Standard Specification, Section 643 Fence. http://www.dot.ga.gov/doingbusiness/theSource/specs/ss643.pdf The Department has established the following guidelines to determine the type of fencing installation appropriate for the access control along the roadway. Full Control of Access: Urban Interstate or Freeway: Ga. Standard Detail 9031-N, Chain Link Wire Fence heavier gage fence typically 6-ft. height typically used in areas with restricted cross section and limited (narrow) space between the roadway and the right-of-way, such as depressed urban freeways with retaining walls and significant changes in vertical elevation between the roadway and right-of-way may include extension arms with barbed wire strands across the top to enhance security. Suburban Interstate or Freeway: Ga. Standard Detail 9031-N, Chain Link Wire Fence or, Ga. Construction Detail F-1, Woven Wire Fence 4-ft. height wire mesh with barbed wire strand along the top and bottom may be used in areas with flatter more rounded sideslopes and wider (more adequate) space between the roadway and the right-of-way. Rural Interstate or Freeway: Ga. Construction Detail F-1, Woven Wire Fence or, Ga. Construction Detail F-6, Game Fence typically 8-ft height mesh with barbed wire strands along the top and bottom - may be used on portions of roadways to reduce crash rates related to wild game crossing. Partial Control of Access or any portion of a roadway with an acquired limit-of-access: Ga. Standard Detail 9031-N, Chain Link Wire Fence or, Ga. Construction Detail F-1, Woven Wire Fence or, Ga. Construction Detail F-6, Game Fence 3.7.2 Fencing on Private Property In cases where the Department is acquiring additional right-of-way or easement, and displacing fence on private property, the value of "replacement fencing" will be assessed by the right-of-way agent for settlement with the property owner. Replacement fencing may be installed by the Department's contractor or by the property owner on private property, as determined in the settlement with the property owner and noted on the plans. GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-13 Fence installed on private property should be offset a minimum of 1-ft outside the state right-of-way line. Typically a 5-ft wide temporary "Easement for the Construction of Fence" will be required on private property if the fence is installed by the Department's contractor. Replacement fencing on private property may consist of chain link wire, woven wire, field fencing/barbed wire, ornamental, or specialty type fencing including gates and associated hardware. In cases where ornamental or specialty fencing is included as a contract item, a special provision with detail drawings will be required in the plans and contract proposal. A decision to provide replacement fencing on private property will be made during right-of-way acquisition. Designers should coordinate with the Right-of-Way Acquisition Manager for direction on replacement fencing on private property prior to establishing temporary easements or adding notes to the plans. For additional guidance involving the installation of fence on private property refer to the GDOT Right-Of-Way Manual, currently maintained by the Office of Right-Of-Way in hard-copy format. 3.8. Right-of-Way Controls Establishing right-of-way widths that adequately accommodate construction, utilities, drainage, and proper roadway maintenance is an important part of the overall design. The border area between the roadway and the right-of-way line should be wide enough to serve several purposes, including provision of a buffer space between pedestrians and vehicular traffic (if applicable), roadway drainage, sidewalk space, lateral offset, clear zone, and an area for both underground and aboveground utilities. A wide right-of-way width allows construction of gentle slopes and also allows for utility poles to be offset further from the road, which in turn results in greater safety for motorists as well as easier and more economical maintenance of the right-of-way. 3.8.1. Rural Areas In hilly terrain, construction limits vary considerably as the roadway passes through cut and fill sections. In these situations, the required right-of-way will likely vary, so it may be impractical to use a constant right-of-way width. In flat terrain, it is usually both practical and desirable to establish a minimum right-of-way width that can be used throughout most of the project length. Required right-of-way widths should be set at even offsets from the centerline, typically multiples of 5-ft., unless some physical feature requires otherwise. As a general rule, the required right-of-way line should be set a minimum of 7-ft. to 10-ft. beyond the proposed limits of construction in cut and 10-ft. to 15-ft. beyond the proposed limits of construction in fill. In areas of high fills a minimum of 20-ft. should be provided beyond the construction limits to provide room for adequate erosion control Best Management Practices (BMPs) that are necessary to minimize sediment transport. Extra right-of-way at the top of cut slopes should be provided for the construction of ditches that will intercept surface drainage and help minimize slope erosion. If a future project will potentially connect to either end of the proposed project, the required right-ofway line is extended to the nearest property line beyond the extent of construction, if practical. This is done to avoid buying right-of-way from the property owner on two different occasions. In this case, the project limit will correspond to the limit of the required right-of-way. GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-14 3.8.2. Urban Areas In urban areas, right-of-way widths are governed primarily by economic considerations, physical obstructions, or environmental considerations. Along any route, development and terrain conditions may vary affecting the availability of right-of-way. It is desirable to set right-of-way in urban areas a minimum of 1-ft beyond the shoulder break point or 2-ft. beyond the greatest required lateral offset specified in Chapter 5. Roadside Safety and Lateral Offset to Obstruction. However, property or environmental impacts may limit the amount of right-of-way that can realistically be acquired. If existing utilities are in conflict within areas of restricted right-of-way, discussions should be held at the Field Plan Reviews to determine how to adequately accommodate utility relocations. 3.8.3. Special Types of Right-of-Way Construction Easement Construction easement is called for on the plans when an area outside the required right-of-way line is needed only during construction of the project. The most common example of this is for construction of a temporary detour road. A permanent feature should not be placed in a construction easement. The decision to obtain permanent right-of-way or construction easement is made after considering the circumstances of each project. The property owner is paid a fee during the time the construction easement is needed. Where applicable, the owner is also paid for damages that may be incurred during the construction process such as for removal of trees or shrubbery. Permanent Drainage Easement Drainage easement is required when a new lateral outfall ditch is to be constructed beyond the right-of-way or when an existing lateral outfall ditch is to be improved outside of the right-of-way. Drainage easement is obtained when construction of these laterals is critical to proper drainage of the project. As with a construction easement the property owner is paid for use of the drainage easement, and for damages resulting from construction. However, with drainage easements GDOT reserves the right of permanent access to the drainage structure for maintenance purposes. Control of Access Access rights may be purchased from property owners along major roadways having full or partial access. No roadway access crossing the limited access is allowed and the property owner is compensated for such restrictions. Where limited access is used along a roadway, it typically extends down intersecting roadways to enhance traffic flow at the intersection. 3.8.4. Accommodating Utilities In addition to primarily serving vehicular traffic, right-of-way for streets and highways may accommodate public utility facilities in accordance with state law or municipal ordinance. The use of right-of-way by utilities should cause the least interference with traffic using the street. If existing utilities are in conflict within areas of restricted right-of-way, discussions should be held at the Field Plan Review to determine how to adequately accommodate utility relocations. Utility GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-15 features, such as power poles and fire hydrants, should be located as close to the right-of-way line as feasible for safety reasons. Utilities located within the limits of construction for the roadway and drainage structures of a project may require relocation, adjustment, or encasement. The surveys should identify the utility locations, elevations, types, sizes, and owners. The plans and cross-sections will then be used to inform utility owners of how the project will impact their facilities. Relocated utilities should normally be accommodated within the required right-of-way. This should be considered in setting required right-of-way limits. For GDOT policies related to accommodating utilities, the designer should refer to the GDOT Utility Accommodation Policy and Standards Manual, which is available at http://www.dot.state.ga.us/doingbusiness/utilities/Pages/manual.aspx 3.9. Value Engineering Value Engineering (VE) is defined in Code of Federal Regulations (CFR) Title 23 Part 627as follows: "the systematic application of recognized techniques by a multi-disciplined team to identify the function of a product or service, establish a worth for that function, generate alternatives through the use of creative thinking, and provide the needed functions to accomplish the original purpose of the project, reliably, and at the lowest life-cycle cost without sacrificing safety, necessary quality, and environmental attributes of the project (). For GDOT guidelines, policies and further information related to VE studies, the designer should refer to the current GDOT PDP, which is available in the "Other Design Related Links and Resources" section of the GDOT Repository for Online Access to Documentation and Standards (ROADS). Any applicable Design Exceptions and Design Variances shall be obtained prior to the implementation of a VE study recommendation which deviates from design standards adopted or defined by this policy. 3.10. Environmental To the extent practical, roadways should be designed to fit into the surrounding landscape and environment. This approach helps to minimize potential impacts to the built and natural environment. Some environmental factors to consider in highway design include: surrounding land uses and landscape elements; historic and cultural resources; important community features; wetlands, streams and other natural resources; utilities and potentially contaminated sites that are close to the roadway; and airports and aviation facilities (located within 2 miles of the project). GDOT encourages proactive coordination with local, and state or federal resource and regulatory agencies to identify important resources that may be of concern on a design project. Various GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-16 techniques can be used to facilitate coordination with local jurisdictions. Several techniques are detailed in the GDOT Context Sensitive Design Online Manual, Section 2.2. Understand Community Input and Values. Sometimes there are opportunities for a roadway project to enhance the surrounding environment. Refer to the GDOT Environmental Procedures Manual as well as the GDOT Context Sensitive Design Online Manual, Section 2.3. Achieve Sensitivity to Social and Environmental Concerns, for further guidance in this area. While designing a roadway or major highway alignment so that it complements the surrounding terrain is an important consideration, any deviation from AASHTO or GDOT design policy standards shall require a Design Exception or Design Variance. Care should be exercised to ensure that applicable local, state, and federal environmental regulations are met in accordance with the project environmental document. GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-17 Chapter 3 Index Arterials Access Control, 9 Rural, 4 Urban, 3 Bicycle Facilities, 6 Buses Design Vehicle. See Design Vehicle, Buses Classification, Functional Arterial, 2 Freeway, 2 Rural Arterial, 4 Urban Arterial, 3 Code of Federal Regulations Title 23 Part 627 - Value Engineering, 16 Cross Section Access Roads, 11 Frontage Roads, 11 Right-of-Way Controls, 1416 Utilities, 1516 Design Context Sensitive Design (CSD), 17 Speed. See Design Speed Vehicles. See Design Vehicles Design Speed, 68 10 mph Speed Reduction, 7 Freeway Ramps, 7 Design Vehicles, 56 Buses, 5 Criteria, 4 Passenger Cars, 5 Recreational Vehicles (RVs), 5, 6 Trucks, 5 Types, 5 Easement Construction. See Right-of-Way, Easement Drainage. See Right-of-Way, Easement Freeways Functional Classification, 2 Interchanges Access Control, 9 Intersections Access Control, 9 Turning Radii, 5 Interstates Access Control, 9 Passenger Cars Design Vehicle. See Design Vehicle, Passenger Cars Ramps Freeways, 7 Recreational Vehicles Design Vehicle. See Design Vehicle, Recreational Vehicles Right-of-Way Easement, Construction, 15 Easement, Drainage, 15 Rural Environment, 14 Urban Environment, 15 Utilities, 15 Width, 1416 Traffic Design Year, 8 Trucks Design Vehicle. See Design Vehicle, Trucks Utilities, 1516 Value Engineering, 16 GDOT Design Policy Manual Revised 4/22/2011 Design Controls 3-18 Chapter 4 Contents 4. ELEMENTS OF DESIGN 1 4.1. Sight Distance 1 4.1.1. General Considerations 1 4.1.2. Stopping Sight Distance 1 4.1.3. Passing Sight Distance 2 4.1.4. Decision Sight Distance 2 4.1.5. Intersection Sight Distance 2 4.2. Horizontal Alignment 4 4.2.1. General Considerations 4 4.2.2. Types of Curves 5 4.2.3. Pavement Widening on Curves 8 4.2.4. Lane Width Transitions and Shifts 9 4.2.5. Transition in Number of Lanes 11 4.3. Vertical Alignments 14 4.3.1. General Considerations for Vertical Alignments 14 4.3.2. Maximum Vertical Grades 16 4.3.3. Minimum Vertical Grades 17 4.3.4. Vertical Curves 19 4.3.5. Maximum Change in Vertical Grade without Using Vertical Curves 20 4.3.6. Vertical Grade Changes at Intersections 20 4.3.7. Minimum Profile Elevation Above High Water 21 4.3.8. Reporting Changes in Vertical Clearances 22 4.4. Combined Horizontal and Vertical Alignments 23 4.4.1. Aesthetic Considerations 23 4.4.2. Safety Considerations 23 4.4.3. Divided Highways 24 4.5. Superelevation 25 4.5.1. Maximum Superelevation Rates 25 4.5.2. Sharpest Curve without Superelevation 27 4.5.3. Axis of Rotation 27 4.5.4. Superelevation Transitions 28 Chapter 4 Index 33 GDOT Design Policy Manual Revised 09/03/2010 Chapter 4 Contents i List of Figures Figure 4.1. Crowned Traveled Way Revolved About Centerline 32 List of Tables Table 4.1. Maximum Horizontal Alignment Deflection without Use of a Curve 8 Table 4.2. Pavement Widening on Curves on Two-Lane Roadways 10 Table 4.3. Miscellaneous Transition Tapers 13 Table 4.4. Turn Lane Transition Tapers 13 Table 4.5. Maximum Vertical Grades 17 Table 4.6. Minimum Vertical Grades for Roadways where Drainage Spread is Considered 19 Table 4.7. Maximum Change in Grade that Does Not Require a Vertical Curve 20 Table 4.8. Vertical Profile Clearances Based on High Water 21 Table 4.9. Maximum Superelevation Rates 26 Table 4.10. Superelevation Rotation Points and Rotation Widths 29 Table 4.11. Maximum Relative Gradients 30 Table 4.12. Adjustment Factor for Number of Rotated Lanes 30 GDOT Design Policy Manual Revised 09/03/2010 Chapter 4 Contents ii 4. ELEMENTS OF DESIGN 4.1. Sight Distance 4.1.1. General Considerations A detailed explanation of how to apply the sight distance criteria to a roadway is described in the American Association of State Highway and Transportation Officials (AASHTO) publication, A Policy on the Geometric Design of Highways and Streets (Green Book), Chapter 3, Design Elements. In addition, Chapter 9 of the Green Book (Intersections) discusses special conditions related to sight distance at intersections. General considerations relating to sight distance noted in the AASHTO Green Book include: Safe and efficient operation of a vehicle is highly dependent on adequate sight distance. Two-lane rural highways should generally provide sufficient passing sight distance at frequent intervals and for substantial distances. Conversely, passing sight distance on two-lane urban streets/arterials is normally of little value. The proportion of a highway's length with sufficient sight distance to pass another vehicle and interval between passing opportunities should be compatible with design criteria pertaining to functional classification, as discussed in this Manual in Chapter 2, Design Policies and Standards. Special consideration should be given to the sight distance requirements at queue backups over a hill, signals, horizontal curves, turning movements, barriers, guardrails, structures, trees, landscaping, vegetation and other special circumstances. 4.1.2. Stopping Sight Distance "Stopping Sight Distance" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for Stopping Sight Distance for roadways in Georgia. A decision to use Stopping Sight Distance values that do not meet the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer. Designers should note that the values for Stopping Sight Distance listed in the AASHTO Green Book are minimum values based on a 2.5 second brake reaction time. Larger stopping sight distance values may be considered by the designer, within the constraints of economic, environmental, social, and other influences. GDOT encourages designers to consider using greater values for Stopping Sight Distance when practical. Stopping sight distance across the inside of curves plays a critical role in determining roadway horizontal curvature and applicable shoulder widths. Enough right of way should be purchased to ensure that adequate stopping sight distance is maintained. There should be no obstruction of sight distance on the inside of curves (such as median barriers, walls, cut slopes, buildings, landscaping materials, and longitudinal barriers). If removal of the obstruction is impractical to provide adequate sight distance, a design may require adjustment in the normal highway cross section or a change in the alignment. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-1 Because of the many variables in alignment, cross section, and in the number, type, and location of potential obstructions, the actual conditions on each curve should be checked and appropriate adjustments made to provide adequate sight distance. The AASHTO Green Book (2004), Exhibit 354 Diagram Illustrating Components for Determining Horizontal Sight Distance, provides additional information on the effects of obstructions located on the inside of horizontal curves. 4.1.3. Passing Sight Distance Passing sight distance is the sight distance needed for passing other vehicles (applicable only on two-way, two-lane highways at locations where passing lanes are not present). 4.1.4. Decision Sight Distance Decision Sight Distance is the distance needed for a driver to detect an unexpected or otherwise difficult-to-perceive information source or condition in a roadway environment that may be visually cluttered, recognize the condition or its potential threat, select an appropriate speed and path, and initiate and complete the maneuver safely and efficiently. Examples of locations where Decision Sight Distance should be considered are: multiphase at-grade intersections, interchanges, ramp terminals on through roadways, lane drops, and areas of concentrated traffic demand where there is likely to be more visual demands and heavier weaving maneuvers. The use of AASHTO Green Book criterion for Decision Sight Distance is encouraged by GDOT and should be considered at appropriate locations along a roadway. In cases where it is not practical to provide Decision Sight Distance, then Stopping Sight Distance shall be provided. 4.1.5. Intersection Sight Distance Intersection Sight Distance has been identified by the Department as having substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for Intersection Sight Distance. Refer to the AASHTO Green Book, Chapter 9, Intersection Sight Distance, for design criteria applicable to the traffic control conditions of an intersection. If it is not practical to provide intersection sight distance values defined by AASHTO, then a decision to select a value or retain an existing condition that does not meet the criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the GDOT Chief Engineer. Appropriate calculations and graphical studies verifying intersection sight distance shall be conducted by the engineer and recorded in the design data book. These studies should be performed during preliminary design when both the horizontal and vertical alignments are being finalized. Graphical studies, at a minimum, should include scaled distances on plan and profile sheets and may at times necessitate plotting the sight line location on specific cross-section sheets. Graphical studies are particularly important for the following conditions: minor road alignment in skew; mainline in horizontal curve; mainline with crest vertical curve on either side of intersection; mainline and/or minor road within a cut; and areas where vegetation growth may obstruct the sight triangles (i.e. grass medians). GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-2 Intersection Sight Distance is critical for urban sections with narrow shoulders and limited right-ofway where obstructions on private property may encroach into the sight triangles. Special consideration should be given to obstructions within the right of way such as: bridges, retaining walls, signs, landscaping, signal control boxes, guardrail, etc. The AASHTO Green Book (2004), Exhibit 354 Diagram Illustrating Components for Determining Horizontal Sight Distance, illustrates and provides further discussion of the affects of obstructions located on the inside of horizontal curves. Angle of Intersection / Skew Angle Ideally, intersecting roadways should meet at or near right angles (90-degrees). This will ensure that the lines-of-sight are optimized for intersection sight distance. "Skew Angle", also a component of Horizontal Alignment, has been identified as standard criteria, having substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. A decision to use a skew angle less than a 60-degree skew angle defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer. Although a minimum 60-degree intersecting angle is permissible by AASHTO standards, it does not provide the benefits of more perpendicular intersections. Therefore, GDOT has adopted a 70-degree skew angle as the minimum skew angle at intersections. A decision to use a skew angle between 60 and 70-degrees shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the Department's Chief Engineer. In general, where there is a high percentage of truck traffic, a 90-degree intersection should be provided. The closer an intersection angle is to 90-degrees, the greater the safety and operational benefits because: exposure time for crossing movements (vehicular and pedestrian) are minimized sharp angle turns (especially for trucks) are reduced driver discomfort is reduced, because drivers will not have to turn their head as much to see the intersection. This is especially true for older drivers who tend to have a decline in head and neck mobility. (1) the bodies of larger vehicles, such as ambulances, motor homes, tractor trailers, etc. tend to interfere with the drivers field of view when at skewed intersection. (2) signing and pavement markings, channelization, and signalization layouts are simplified When a "T" intersection becomes a four-way intersection due to extension of an existing side street or construction of a driveway opposite the side street, the new facility will usually be built at or very nearly 90-degrees to the mainline. Cross traffic operations are much safer and more efficient if the existing side street leg is at the same angle. The condition is very likely to occur on divided highways where development is concentrated at established median breaks. The AASHTO Green Book acknowledges that sharp curves may be as great a hazard as the acuteangle crossing itself. However, rather than omitting the curves and retaining the acute-angle crossing, the effect of the curves should be mitigated. For example, warning signs for reduction of speed in advance of such curves could be provided. This is especially appropriate for "T" intersections and cross roads with low volumes of through traffic. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-3 (1) FHWA. Highway Design Handbook for Older Drivers and Pedestrians, 2001. The 2001 version of this publication is available online at http://www.tfhrc.gov/humanfac/01103/coverfront.htm (2) MBTC FR 1073. Intersection Angle Geometry and the Driver's Field of View, 1997. http://ww2.mackblackwell.org/web/research/ALL_RESEARCH_PROJECTS/1000s/1073-gattis/MBTC1073.pdf Right-of-Way Flares The preferred method to ensure adequate intersection sight distance is to acquire the area(s) within the sight triangles as right of way so the area can be properly managed and kept free of obstructions. These areas are referred to as right-of-way flares. Right of way Flares should be obtained in order to maintain adequate intersection sight distance at intersections. 4.2. Horizontal Alignment "Horizontal Alignment" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for elements of horizontal alignment. A decision to deviate from the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer. The location and alignment selected for a highway are influenced by factors such as physical controls, environmental considerations, economics, safety, highway classification and design policies. The horizontal alignment cannot be finalized until it is coordinated with the vertical alignment and cross section elements of the roadway. Horizontal curves should be used for all deflections in a horizontal alignment, with the exception of alignment changes without horizontal curves as discussed in detail in Section 4.2.2. Types of Curves of this Manual. In special situations, such as roadway reconstruction or widening on existing alignment, practicality will dictate when deflection angles (PI without a curve) may be introduced in lieu of horizontal curvature. Spiral curves are generally not utilized on Georgia roadways. Refer to the AASHTO Green Book Chapter 3, Elements of Design, when determining the radii of horizontal curves and corresponding superelevation (if applicable). Wherever possible, minimum curve radii and maximum superelevation rates should be avoided for any given speed design. 4.2.1. General Considerations See the Green Book Chapter 3 "General Controls for Horizontal Alignment" section for general considerations when setting a horizontal alignment. In general, the number of short curves should be kept to a minimum. Long tangents are needed on two-lane highways such that sufficient passing sight distance is available on as great a percentage of the roadway as possible. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-4 Sharp curvature should be avoided near the following locations: elevated structures; at or near a crest in grade; at or near a low point in a sag or grade; at or near intersections, transit stops, or points of ingress or egress; and at or near decision points. The concepts of stopping sight distance, intersection sight distance, decision sight distance and driver expectancy should be considered during the development of horizontal alignments. If possible, the horizontal alignments of roadways should be free of curvature in and around intersections, interchanges, bridges, railroad crossings, toll plazas, drop lanes and roadside hazards. To facilitate pavement drainage, alignments should be laid out such that the 0% cross slope flat points associated with superelevation transitions on either end of a horizontal curve (if applicable) does not correspond to low points in the roadway vertical profile. Superelevation is discussed in this Manual in Section 4.5. The horizontal alignment should be coordinated carefully with the vertical profile design. This subject is discussed in further detail in this Manual in Section 4.4. The design speed of successive horizontal curves on ramps can vary as vehicles are often accelerating or decelerating. A common rule to apply to the speed design of ramps is that the design speed of the first curve of an exit ramp can be assumed to be 10 mph less than the design speed of the mainline. With each successive curve on the exit ramp, the design speed of the curve may be reduced based on computed vehicle deceleration. The process is to be reversed for entrance ramps, i.e., the design speed for curves will successively increase until the design speed of the last curve before the mainline is 10 mph less than that of the mainline. For additional considerations and guidance in setting horizontal alignments, refer to of the AASHTO Green Book Chapter 3, Elements of Design - General Controls for Horizontal Alignment. 4.2.2. Types of Curves The following types of curves are discussed in this section: circular curves compound curves reverse curves spiral curves broken back curves curves with small deflection angles minimum length of horizontal curve alignment changes without horizontal curves Circular Curves GDOT typically uses the arc definition of the circular curve. Under this definition, the curve is defined by the degree of curve (D ), which is the central angle formed when two radial lines at the a center of the curve intersect two points on the curve that are 100-ft. apart, measured along the arc of the curve. D = 18,000 / ( * R) a GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-5 Where: D = Degree of Curve (degrees) a R = Radius of Curve ( ft.) L = (100 * I)/ D a Where: L = Length of Curve ( ft.) D = Degree of Curve (degrees) a I = Total deflection of curve (degrees) Compound Curves Compound curves involve two horizontal curves of different radii sharing a common point for their point of tangent (PT) and point of curve (PC), respectively. For open highways, compound curves between connecting tangents should be used only where existing topographic controls make a single simple curve impractical. Guidance regarding compound curves falls into two categories: Roadways (excluding ramps), one-way or two-way - The radius of the flatter curve should not exceed the radius of the sharper curve by more than 50% (a ratio of 1.5:1). Ramps - A ratio as great as 1.75:1 may be used on one-way interchange ramps, where compound curves are more common. Ratios greater than 2.0:1 are strongly discouraged. The compound radii ratio criteria are only applicable when the curve radii decreases from one curve to the next in the direction of travel. Reverse Curves Any abrupt reversal in alignment should be avoided. A reversal in alignment can be suitably designed by including a sufficient length of tangent between the two curves to provide adequate superelevation transitions. See Section 4.4. Combined Horizontal and Vertical Alignments for additional discussion of superelevation transition lengths. The tangent distance between reverse curves should be the distance (based on the appropriate gradient or ratio) to rotate from 2/3 of the full superelevation rate of the first curve to 2/3 of the full superelevation rate of the second curve. For roadways with design speeds less than or equal to 45 mph, a minimum tangent of 100-ft. should be provided between reverse curves, even if superelevation is not required. With or without superelevation, extreme physical constraints may dictate the use of a reverse curve with a 0-ft. length tangent (the PT of the first curve and the PC of the second curve are at the same location). In this case, the 0% cross slope point should be placed at the shared PT/PC and use the best possible superelevation transition ratio. Where it is impractical to provide a tangent length capable of incorporating the superelevation runoff lengths and the tangent run out lengths of both superelevated curves, the 0% cross slope point should be placed at a point derived from the best possible superelevation transition ratio between the two curves (not necessarily the center of the tangent). For an expanded discussion of superelevation refer to Section 4.4. Combined Horizontal and Vertical Alignments. On higher-speed roadways (design speeds greater than 45 mph), curves that do not require superelevation are so flat that no tangent between the curves is necessary. However, wherever practical, a 150-ft. minimum tangent should be introduced between reverse curves. On higherspeed roadways with curves requiring superelevation, a tangent length suitable for accommodating GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-6 the necessary superelevation transition should be provided (see Section 4.4. Combined Horizontal and Vertical Alignments). For reverse curves on a roadway with a design speed greater than 45 mph, the use of tangent lengths less than those calculated by AASHTO procedures shall require a design exception. Spiral Curves Spiral curves are generally not utilized on Georgia roadways, except in special cases. For overlay or widening projects, existing spiral curves may remain. For roadways to be re-constructed, existing spiral curves may be replaced with simple curves, unless existing property improvements or other controls make this impractical. Refer to the AASHTO Green Book Chapter 3, Elements of Design, for additional information on spiral curves. Railroads typically utilize spiral curves at the beginning and end of each simple horizontal curve. A project involving a railroad crossing and possibly track relocation may require the use of spiral curves. For additional information related to the design of railroad alignments (including spiral curves), refer to the American Railway Engineering and Maintenance-of-Way Association (AREMA) Manual for Railway Engineering. Broken-Back Curves Successive curves in the same direction that are separated by a short tangent are known as broken-back curves. GDOT defines this short tangent as one with a length less than: 15*V for design speeds less than or equal to 45 mph, or 30*V for design speeds greater than 45 mph. In these equations, V is the design speed in mph. Broken-back curves are very undesirable from both an operational and an appearance standpoint. While it may not be feasible or practical in some situations to completely eliminate broken-back curves, every effort should be made to avoid this type of alignment if possible by separating, combining, or compounding curves in the same direction. Curves with Small Deflection Angles A short horizontal curve with a small deflection angle (less than five degrees) may appear as a kink in the roadway. As a minimum, curves should be at least 100-ft. in length for every one degree of central angle. Minimum Length of Horizontal Curve The minimum length of horizontal curve should be in accordance with the following: L = 15*V Where: L = minimum curve length (ft.) V = design speed (mph) On high-speed controlled-access facilities that use large-radius curves, the minimum length of horizontal curve should be in accordance with the following: L = 30*V Where: L = minimum curve length (ft.) V = design speed (mph) GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-7 Alignment Changes without Horizontal Curves There may be instances where existing constraints will make it impractical to utilize horizontal curves which maintain the minimum length criteria specified in the first seven cases cited in Section 4.2.1. Horizontal Alignment General Considerations. Right-of-way, cost, or environmental constraints could be prohibitive on widening, reconstruction, maintenance, safety, and 3R projects in both urban and rural settings. When situations warrant, slight deflection angles may be introduced to (or maintained on) the roadways horizontal alignment. These angles will be very slight so that they do not adversely affect safety or operations. Acceptable angles of deflection will depend on the design speed of the facility. Table 4.1. lists the maximum angle of horizontal deflection for roadways in Georgia. Table 4.1. Maximum Horizontal Alignment Deflection without Use of a Curve Design Speed (MPH) Maximum Angle of Horizontal Deflection (minutes) 15 120 The use of horizontal curves is preferable to deflection angles. However, there are cases where small deflections are acceptable. For example, as shown in Table 4.1, an existing deflection angle up to 14 minutes (imperceptible to the eye) on an interstate widening project (design speed 70 mph) may be maintained. 20 90 At intersections with an all-way stop condition (with no 25 60 foreseeable signalization) and some form of constraint, 30 45 there may be a break in the roadway alignment as much 35 40 as five degrees (at the centerline crossing in the 40 35 intersection), provided intersection sight distance is 45 30 maintained in all directions. 50 25 4.2.3. Pavement Widening on Curves 55 20 60 18 On modern highways and streets that feature 12-ft. lanes and high-type alignments, the need for widening on 65 16 curves has decreased considerably in spite of high 70 14 speeds. In many cases, degrees of curvature and 75 12 pavement widths established by policies in this Design 80 10 Manual preclude the necessity of pavement widening on roadway curves. This is especially true if the alignments are as directional as practical, consistent with the topography, and developed properties and community values are preserved (refer to Section 4.2.1. General Considerations). However, for some conditions of speed, curvature, and width, it may still be necessary to widen pavements. Widening should be evaluated at the following locations: low speed roadways with near maximum curvature ramps connecting roadways where curves sharper than those specified in this Manual are used Specific values for pavement widening in curves are shown in Table 4.2. Pavement Widening on Curves on Two-Lane Roadways. For additional discussion and widening values, refer to the AASHTO Green Book, Chapter 3. Elements of Design Traveled Way Widening on Horizontal Curves. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-8 4.2.4. Lane Width Transitions and Shifts Lane width transitions can occur at several locations including: Lane width transitions which are to be developed for curves (see Section 4.2.3. Pavement Widening on Curves) Connections to existing pavement such as pavement tapers which occur at the back of a turnout on an existing side road Transitions to a wider lane such as a truck lane or a one-way, one-lane ramp Mainline lane shifts in advance of an intersection Mainline lane shifts in advance of a typical section change such as the addition of a mainline lane Mainline lane shifts in advance of a typical section change such as a change in median width There are two methods by which an alignment transition or "shift" may be accomplished: The first method is to treat the transition or shift as though it were any other required alignment change. With this approach, a transition or shift would be accomplished through the use of a series of reverse curves. Quite often, the use of curve radii which do not require superelevation result in a length of transition greater than that required by providing a taper. Superelevation should be utilized if warranted by normal procedures. The second method of accomplishing a transition or "shift" involves the use of tapers. Tapers are acceptable provided the following two conditions exist: The alignment shift is consistent with the cross slope of the roadway and does not require "shifting" over the top of an existing pavement crown The direction of the shift is not counter to the pavement cross-slope (from a superelevation or reverse-crown consideration) GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-9 Table 4.2. Pavement Widening on Curves on Two-Lane Roadways Degree Curve Radius (ft.) 30 (mph) 24-ft. Roadway 40 50 60 (mph) (mph) (mph) 70 (mph) 30 (mph) 22-ft. Roadway 40 50 60 (mph) (mph) (mph) 70 (mph) 30 (mph) 20-ft. Roadway 40 50 (mph) (mph) 60 (mph) 1.00 5,729.58 0.0 0.0 0.0 0.0 0.0 0.5 0.5 0.5 1.0 1.0 1.5 1.5 1.5 2.0 2.00 2,864.79 0.0 0.0 0.0 0.5 0.5 1.0 1.0 1.0 1.5 1.5 2.0 2.0 2.0 2.5 3.00 1,909.86 0.0 0.0 0.5 0.5 1.0 1.0 1.0 1.5 1.5 2.0 2.0 2.0 2.5 2.5 4.00 1,432.39 0.0 0.5 0.5 1.0 1.0 1.0 1.5 1.5 2.0 2.0 2.0 2.5 2.5 3.0 5.00 1,145.92 0.5 0.5 1.0 1.0 1.5 1.5 2.0 2.0 2.5 2.5 2.5 3.5 6.00 954.93 0.5 1.0 1.0 1.5 1.5 2.0 2.0 2.5 2.5 3.0 3.0 7.00 818.51 0.5 1.0 1.5 1.5 2.0 2.5 2.5 3.0 3.5 8.00 716.20 1.0 1.0 1.5 9.00 636.62 1.0 1.5 2.0 2.0 2.0 2.5 2.0 2.5 3.0 3.0 3.0 3.5 3.0 3.5 4.0 10.18 562.64 1.0 1.5 12.24 488.04 1.0 2.0 2.0 2.5 2.5 3.0 3.0 3.5 3.5 15.30 374.48 2.0 3.0 4.0 19.35 296.10 2.5 3.5 4.5 22.42 255.59 3.0 4.0 5.0 26.44 216.69 3.5 4.5 5.5 Notes: 1. Values for widening (ft.) for two-lane roadways - one-way or two-way traffic 2. Disregard values less than 2.0-ft. (above heavy line and not within highlighted area) for two-lane (one-way or two-way traffic) pavements 3. For three-lane and four-lane undivided roadways multiply values by 1.5 and 2.0, respectively and round to the nearest 0.5-ft. If values are less than 2.0-ft., disregard 4. Pavement widening is intended for utilization where truck traffic is significant and the increase in pavement width is to be 2.0-ft. or greater 5. Locations for pavement widening shall be shown in the construction plans or specified by the Engineer 6. Pavement widening to occur along the inside of the normal curve. Additional width is to be shared equally by all lanes. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-10 Taper lengths associated with shifts on Georgia roadways should be calculated as: Case 1 Design Speed 45 mph: L = W * s (W * s2 ) Case 2 Design Speed < 45 mph: L 60 Where: L = distance needed to develop widening (ft) W = width of lane shift (ft) s = design speed (mph) Note: the Case 1 and Case 2 taper lengths described above are applicable to permanent conditions. For a more detailed discussion on temporary conditions associated with construction, refer to Chapter 12. Stage Construction. 4.2.5. Transition in Number of Lanes Instances where the number of lanes on a roadway is transitioning fall into two categories lane additions and lane drops. Lane drops induce a merge situation. Adequate distance for drivers to perform the merge maneuver should thus be provided. Lane additions that do not involve a shift of the mainline lanes may be accomplished in a much shorter distance. Lane Drops Lane drops can occur in many situations on all types of roadways, such as: mainline lane drop due to traffic drop off mainline lane drop to meet lane balance requirements (limited access) mainline lane drop due to transition to non-widened section, etc. end of auxiliary lane end of collector-distributor (cd) system end of climbing lane ramp merges on limited access facilities With three exceptions, lane drops (or merges) for the situations listed above should be designed based on the minimum convergence tapers provided in Section 4.2.4. Lane Width Transitions and Shifts. Exception 1 For lane drops and merges on high-speed Limited Access facilities, where design year mainline peak hour traffic rates exceed 1,550 vehicles per lane (LOS C), the convergence ratio should be: L = 2 * W * s Where: L = distance needed to develop widening (ft) W = width of lane shift (ft) s = design speed (mph) GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-11 Exception 2 Certain situations require the use of horizontal curves and possibly superelevation in association with lane reductions. An example of this would be tie-ins being constructed on projects between a proposed four-lane section (with 44-ft. median) and a two-lane existing section. In these situations, a lane should first be dropped using the taper rates specified in Section 4.2.4. Lane Width Transitions and Shifts, while still on the fourlane section (in advance of the crossover). Once the lane reduction has been attained, the tie-in to the two-lane section should be accomplished with a tie-in using AASHTO horizontal curves and superelevation rates appropriate for the design speed of the facility. If possible, the curves associated with the tie-in should be no sharper than 1 degree. Exception 3 If a ramp merge occurs on a significant upgrade, the speed differential of a truck or bus merging into traffic should be evaluated. In general, if the mainline grades exceed 3% (upgrade in merge), the convergence ratio should be: L = 2 * W * s Where: L = distance needed to develop widening (ft) W = width of lane shift (ft) s = design speed (mph) General Rules on Lane Drops lane drops on limited access facilities should occur at exits lane drops on limited access facilities should occur on the outside lanes upon departing an intersection, a lane (to be dropped) should be maintained for a minimum of 800-ft. from the intersection before initiating the lane drop tapers associated with multiple, successive lane drops on the mainline should be separated by a minimum 1,000-ft. tangent section Lane Additions Lane additions that are not accompanied by a mainline alignment shift can be performed over a relatively short distance. A minimum 15:1 expansion taper rate should be provided. However, when spatial constraints exist, expansion tapers may be as low as 5:1 (urban) and 8.33:1 (rural). Required lane addition taper lengths associated with median breaks and intersections can utilize taper rates less than those pertaining to through lanes. GDOT Construction Standards and Details, Construction Detail M-3 depicts turn lane taper lengths associated with Type A, B and C medians. Table 4.3. Miscellaneous Transition Tapers summarizes taper length and taper ratio requirements as they pertain to the addition of left-turn and right-turn lanes in Georgia. The designer should attempt to meet the values found in this table. However, if constraints such as right-of-way, environmental impacts, utility conflicts and/or driveway/access issues exist, the minimum values may be utilized. When a lane addition occurs due to the generation of a center lane or a passing lane (i.e., when a two-lane road is to be widened to a three-lane section) the transition tapers must follow the guidelines discussed in Section 4.2.4. Lane Width Transitions and Shifts. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-12 Table 4.3. Miscellaneous Transition Tapers Location Driveways Driveways Parallel Ramps on Limited Access Facilities Entrance Parallel Ramps on Limited Access Facilities Exit Design Speed (mph) < 45 > 45 Varies Varies Transition Width, W (ft.) 12 12 12 12 Minimum Taper (ft.) 50 100 250 250 If the widening will be asymmetric or will occur only to one side, the transition width (W) is the width of the additional lane. If the widening will be symmetric, i.e., both directions of travel bifurcate symmetrically to create a center lane, then the transition width (W) can be assumed to be of the width of the additional lane. For instance, if a 14-ft. center turn lane was being generated symmetrically on a 55 mph two-lane roadway, the taper length would be: L (14.0) *55 385.0 ft. 2 A summary of other special cases for transition tapers is included in Table 4.3. Miscellaneous Transition Tapers. Turn Lanes in an Intersection, Median or Driveway Refer to Table 4.4. for a general guideline on minimum and desirable turn lane transition taper values. Table 4.4. Turn Lane Transition Tapers Design Speed (mph) Urban or Rural Type A Median > 45 Rural > 45 Rural > 45 Rural Type B Median > 45 Rural > 45 Rural > 45 Rural Type C Median < 45 Urban* Flush Median > 45 Rural Median Width (ft.) 40 44 64 32 44 64 20 14 Transition Width, W (ft) 12 12 12 4 16 26 12 14 Minimum Left Turn Right Turn Taper Ratio Taper Length (ft.) Taper Ratio Taper Length (ft.) 8.33:1 100 8.33:1 100 8.33:1 100 8.33:1 100 8.33:1 100 8.33:1 100 15:1 60 8.33:1 100 15:1 240 8.33:1 100 15:1 390 8.33:1 100 5:1 60 8.33:1 100 8.33:1 116 8.33:1 100 Desirable Left Turn Right Turn Taper Ratio Taper Length (ft.) Taper Ratio Taper Length (ft.) 15:1 180 15:1 180 15:1 180 15:1 180 15:1 180 15:1 180 15:1 60 15:1 180 15:1 240 15:1 180 15:1 390 15:1 180 15:1 180 15:1 180 15:1 210 15:1 180 > 45 Rural Varies 14 8.33:1 116 8.33:1 100 15:1 210 15:1 180 * An urban section with a Type C Median can be used for design speeds of 45 mph GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-13 4.3. Vertical Alignments "Vertical Alignment", "Grade" and "Vertical Clearance" have been identified as "controlling criteria" that have substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for elements of vertical alignment, grade and vertical clearance. A decision to deviate from the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer. GDOT uses design controls for crest and sag vertical curves based on sight distance. The AASHTO Green Book Chapter 3, Elements of Design, provides additional discussion on rates of vertical curvature (K). Maximum allowable vertical grades are dependent on the classification of the facility and are discussed in the following AASHTO Green Book chapters: Chapter 5. Local Roads and Streets Chapter 6. Collector Roads and Streets Chapter 7. Rural and Urban Arterials Chapter 8. Freeways GDOT typically uses symmetrical parabolic vertical curves at changes in grade. Exceptions to this include spot locations such as alignment breaks near intersections and overlay transitions where vertical grade breaks can be accomplished without the use of vertical curves. The maximum grade break (%) varies based on the design speed of the facility. 4.3.1. General Considerations for Vertical Alignments The following are general considerations for vertical alignments: Maximizing sight distances should be a primary consideration when establishing vertical alignment. Long, gentle vertical curves should be used wherever possible and appropriate. "Roller coaster" or "hidden dip" profiles should be avoided by using gradual grades made possible by heavier cuts and fills or by introducing some horizontal curvature in conjunction with vertical curvature. The "roller coaster" may be justified in the interest of economy and may be acceptable in low-speed conditions, but is aesthetically undesirable. A single long vertical curve is preferred over "broken-back" grade lines (two crest or two sag vertical curves separated by a short tangent). Use a smooth grade line with gradual changes, consistent with the type of highway and character of terrain, rather than a line with numerous breaks and short lengths of tangent grades. On a long ascending grade, it is preferable to place the steepest grade at the bottom and flatten the grade near the top. Moderate grades should be maintained through intersections to facilitate turning movements. Grades should not exceed 6%, and 3% maximum is preferred. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-14 Sag vertical curves should be avoided in cuts as roadway flooding or ponding conditions may occur at these locations should the drainage system become clogged or overburdened. Vertical grades should be coordinated with required acceleration and deceleration areas, wherever possible. For instance, at an interchange, it is preferable for the crossing roadway to go over the limited access facility. That way, vehicles are on an upgrade as they decelerate towards a stop condition and are on a downgrade as they are entering the limited access facility. As much as possible, the vertical alignment should be closely coordinated with the natural topography, available right of way, utilities, roadside development, and existing drainage patterns. Vertical alignments should be properly coordinated with environmental constraints (e.g., encroachment into wetlands). When a vertical curve takes place partly or wholly in a horizontal curve, the vertical curvature should be coordinated with the horizontal curvature. See Section 4.4. Combined Horizontal and Vertical Alignments. When one roadway is in a tangent section and an intersecting roadway has a continuous vertical grade through an intersection, consideration should be given to rotating the pavement cross slope on the tangent roadway to a reverse crown to better match the profile of the intersecting roadway. Standard superelevation transition rates would apply. Additional considerations for setting vertical alignments are detailed in the AASHTO Green Book Chapter 3, Elements of Design. Factors That Influence Roadway Grades There are several factors that influence roadway grades: topography and earthwork control points at the beginning and end of the project vertical clearances for drainage structures intersecting railroads applicable glide slopes for roadways near airports intersecting roads and streets driveway tie-ins existing bridges to remain vertical clearances at grade separations vertical clearances for high water and flood water proposed new bridges driver expectancy at intersections GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-15 4.3.2. Maximum Vertical Grades The grades selected for vertical alignments should be as flat as practical, and should not exceed the values listed in Table 4.5 Maximum Vertical Grades. Maximum values vary based on types of terrain, facility classification, and design speed. The maximum design grade should be used infrequently; in most cases, grades should be less than the maximum design grade. In Table 4.5. Maximum Vertical Grades, industrial roadways are defined as local and collector streets with significant (15% or more) truck traffic. Exceptions to the maximum vertical grades listed in Table 4.5. are as follows: For short sections less than 500-ft. and for one-way downgrades, the maximum grade may be 1% steeper than the values listed in Table 4.5. The maximum vertical grade for local streets, collectors and arterials may be increased by as much as 2% under extreme conditions Maximum values in Table 4.5. may be reduced when upgrades cause a speed reduction greater than or equal to 10 mph. For streets and highways requiring long upgrades, the maximum grade should be reduced so that the speed reduction of slow-moving vehicles (i.e., trucks and buses) is not greater than 10 mph. Where reduction of grade is not practical, climbing lanes should be provided to meet these speed reduction limitations. A design exception is required where a climbing lane cannot be provided and grade cannot be reduced. Climbing lanes, speed reductions on upgrades and the critical lengths of grade associated with speed reductions are concepts that are discussed in detail in the AASHTO Green Book Chapter 3, Elements of Design. These concepts should be considered and appropriate provisions should be incorporated into any facility in which vertical grades will cause a significant (10 mph or more) reduction in the speed of a slow-moving vehicle. American's with Disabilities Act (ADA) Requirements That Influence Maximum Vertical Grades Relative to roadway profiles, ADA requirements dictate that: The running (or longitudinal) slope of sidewalks should not exceed 5%. In urban and suburban situations where the roadway typical section includes curb and gutter, the sidewalk is normally located behind (and adjacent to or offset from) the roadway. Since topography and practicality often dictate that many curb and gutter roadways have longitudinal slopes in excess of 5%, the running slope of sidewalks often exceed 5%. Currently, GDOT interprets the ADA requirements for running slope to be applicable only to sidewalk ramps not to longitudinal sidewalks paralleling curb and gutter roadways. However, GDOT recognizes the merit in attempting to limit longitudinal sidewalk slopes wherever possible. With regard to sidewalks, longitudinal slopes and mainline roadway profiles, GDOT offers the following approach: o On new alignment urban roadways, roadway grades should be limited to 5%, wherever practical. Applicable overriding constraints include environmental, right-ofway, cost, topography, and context-sensitive design areas. The maximum values in Table 4.5. may be used, if necessary. o When an existing urban roadway is to be reconstructed, the practicality of vertical reconstruction by limiting proposed grades to 5% should be evaluated. If this GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-16 approach is found to be impractical or technically infeasible (see above), the maximum values in Table 4.5. may be used, if necessary. In either a new location or existing reconstruction situation where roadway grades exceed 5%, the following should be considered: o Provision of pedestrian signage and connections to an alternate pedestrian route which does not have running slopes greater than 5%. This can be a footpath parallel to the roadway (but not adjacent to the sidewalk) or a detour route. The cross slope of cross walks at intersections should not exceed 2%. To the extent practical, profile grades and cross slopes in intersections should be minimized ideally to 2%. Where this is not technically feasible, profile grades and cross slopes in urban intersections may exceed 2%. 4.3.3. Minimum Vertical Grades Minimum vertical grades are typically used to facilitate roadway drainage. This is especially true of curbed roadway sections where drainage or gutter spread is a consideration. Uncurbed Pavements For projects involving uncurbed pavements, longitudinal grades may be flat (0%) in areas where appropriate cross slopes are provided. In areas of superelevation transitions and/or flat cross slopes on those projects, minimum vertical grades should be consistent with those listed in Table 4.6. Minimum Vertical Grades for Roadways where Drainage Spread is a Consideration. However, there are situations with uncurbed pavements where it is prudent that consideration be given to maintaining minimum vertical grades - similar to those for curbed roadway sections. These situations include: a new location rural section roadways with high truck percentages that experience appreciable pavement rutting current rural roadways in urban, suburban or developing areas that have a realistic chance of being converted to a curb and gutter sometime in the foreseeable future areas containing superelevation transitions and/or flat cross slope areas interstate or other high speed facilities Type of Terrain Industrial Roadways Level Rolling Mountainous Local Rural Roads Table 4.5. Maximum Vertical Grades Maximum Grade (%) for Specified Design Speed (mph) 15 20 25 30 35 40 45 50 55 60 65 70 75 80 - - 44443333 - - - - - 55554444 - - - - - 66665555 - - - - GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-17 Type of Terrain Table 4.5. Maximum Vertical Grades Maximum Grade (%) for Specified Design Speed (mph) 15 20 25 30 35 40 45 50 55 60 65 70 75 80 Level 9877777665 - - - - Rolling 12 11 11 10 10 10 9 8 7 6 - - - - Mountainous Local Urban Streets Level 17 16 15 14 13 12 11 10 10 - - - - 12 11 11 10 10 9 9 8 8 - - - - - Rolling 14 13 12 11 11 10 10 9 - - - - - - Mountainous Rural Collectors Level 17 16 15 14 13 12 11 - - - - - - - 777777665 - - - - Rolling - 10 10 9 9 8 8 7 7 6 - - - - Mountainous Urban Collectors Level - 12 11 10 10 10 10 9 9 8 - - - - 999998776 - - - - Rolling - 12 12 11 10 10 9 8 8 7 - - - - Mountainous Rural Arterials Level - 14 13 12 12 12 11 10 10 9 - - - - - - - - 554433333 Rolling - - - - - 665544444 Mountainous Urban Arterials Level - - - - - 877665555 - - - 8776655 - - - - Rolling - - - 9887766 - - - - Mountainous - - - 11 10 10 9 9 8 8 - - - - Rural and Urban Freeways (Limited Access Facilities) Level - - - - - - - 4433333 Rolling - - - - - - - 5544444 Mountainous - - - - - - - 66655 - - GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-18 Curbed Pavements For curbed pavements, minimum longitudinal grades are controlled by the values in Table 4.6. This includes Table 4.6. Minimum Vertical Grades for Roadways where Drainage Spread is a Consideration roadways with concrete median barriers or side barriers, V-gutter and those roadways adjacent to walls. These values will generally ensure that roadway "spread" is not Type of Facility Industrial Roadways with Curb and Gutter Local Urban Streets with Curb and Gutter Minimum Grade (%) Desirable Minimum 0.30 0.20 0.30 0.20 excessive and can be contained Urban Collectors with Curb and Gutter 0.50 0.30 within acceptable ranges by a Urban Arterials with Curb and Gutter 0.50 0.30 minimum (reasonable) number of Urban Freeways or Limited Access Facilities 0.50 0.30 roadway drainage catch basins. The minimum values in Table 4.6 should be used only under extreme conditions. 4.3.4. Vertical Curves In almost all cases, changes in grade should be connected by a parabolic curve (the vertical offset being proportional to the square of the horizontal distance). Vertical curves are required when the algebraic difference of intersecting grades exceeds a minimum threshold (refer to Section 4.3.5. Maximum Change in Vertical Grade without Using Vertical Curves). Refer to the AASHTO Green Book Chapter 3, Elements of Design Vertical Curves, for considerations that must be made for vertical curves. General Considerations Vertical alignment has significant effect on roadway drainage. Special consideration should be given to the following: Curbed roadways should have a minimum grade of not less than the values specified in Section 4.3.3. Minimum Vertical Grades in order to avoid excessive gutter spread. This includes roadways with concrete median barriers or side barriers, and V-gutter. Non-curbed roadways should maintain a minimum grade consistent with the directives of Section 4.2.3. Pavement Widening on Curves and Section 4.3.3. Minimum Vertical Grades For drainage purposes, the K value should not exceed 167 for curbed roadways (crest or sag verticals). In cases where design speeds are higher than 65 mph, this criteria does not apply. For curbed roadways in sag vertical curves with low points, a minimum grade of 0.30% should be provided within 50-ft. of the low point. This corresponds to a K value of 167. The minimum K values as defined by AASHTO are based on the assumption that there are significant tangent sections on either side of the vertical curve. Therefore, when using compound or unsymmetrical vertical curves, sight distances should be checked graphically to ensure that adequate sight distance is provided. Additional information can be found in the National Cooperative Highway Research Program (NCHRP) Report 504 Design Speed, Operating, Speed, and Posted Speed Practices. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-19 In establishing the vertical alignment, sound engineering practice should be used to strike a reasonable balance between excavation (cut) and embankment (fill). Other overriding factors must also be considered, including: maintenance of traffic environmental impacts right-of-way impacts pedestrian (ADA) requirements safety considerations sight distance considerations (all types) drainage considerations high water considerations ability to tie the roadway profile into side roads, driveways and at grade railroad crossings. drivability and driver expectancy 4.3.5. Maximum Change in Vertical Grade without Using Vertical Curves GDOT typically uses vertical curves for changes in vertical grades. However, there are situations where it is either impractical or impossible to utilize a vertical curve. Such situations include: temporary vertical tie-ins profile tie-ins such as overlay transitions avoidance and/or minimization of an environmental impact point profiles in overlay and widening sections profile reconstruction near fixed objects such as bridges and approach slabs Table 4.7. lists the maximum vertical grade changes that do not require a vertical curve. Note that these values change per design speed. Grade breaks should only be used when necessary (vertical curves should be used, wherever practical). If two or more of these vertical grade breaks are utilized in succession (i.e., a point profile), the cumulative effect of these grade breaks in the profile shall be evaluated for stopping sight distance and it shall be verified that typical stopping sight distance is always provided. If the cumulative effect of a series of vertical grade breaks violates stopping sight distance criteria, the values in Table 4.7. may need to be reduced. Maximum Change in Grade (%) Table 4.7. Maximum Change in Grade that Does Not Require a Vertical Curve Design Speed (mph) 20 25 30 35 40 45 50 55 60 65 70 1.20 1.10 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 4.3.6. Vertical Grade Changes at Intersections If it is impractical to match the elevation of an intersecting road, the crossroad should be reconstructed for a suitable distance using adequate vertical geometry to make the grade adjustment. In general, a 2% maximum tangent grade break is allowed at the edges of signalized GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-20 intersections to allow vehicles on the crossroads to pass through an intersection on a green signal safely without significantly adjusting their speed. A 4% maximum grade break is allowed in the center of an intersection corresponding to the 4% crown breakover associated with a crossing road. For the edges of unsignalized or stop condition intersections, a maximum tangent grade break of 4% may be employed. 4.3.7. Minimum Profile Elevation Above High Water One major factor in establishing a vertical profile for either a roadway or a bridge is clearance over high water or a design flood. For roadways, this is important for two reasons: Pavement Protection - A major factor in a roadway's durability is minimizing the amount of moisture in the base and pavement. Keeping the roadway base as dry as possible will help prevent or minimize pavement deterioration. Safety - A roadway with a profile set above the design high water will keep water from overtopping the roadway. Overtopped roadways are a hazard to moving vehicles and can effectively shut down a facility when they are needed most, i.e., a hurricane evacuation route. For bridges, prescribed low-chord clearances must be maintained to protect the bridge superstructure from unanticipated lateral forces associated with high-velocity flood waters. Table 4.8. summarizes the required high water clearances for roadways and bridges in Georgia. A vertical profile that satisfies the worst-case situation for either clearance or overtopping shall be established. Table 4.8. Vertical Profile Clearance Based on High Water Facility Interstate Hurricane Evacuation Routes Roads Designed as State Routes Roads Not Designed as State Routes ADT: 0 99 ADT: 100 399 ADT: 400 1,499 ADT: 1,500 or more Driveways Temporary Detours Permanent Bridges Temporary Bridges Local Road with ADT < 400 All Other Roads Designer's First Priority Roadway Base Bridge Low Chord Clearance Required Clearance 1-ft 1-ft. 1-ft. Design Flood Frequency 50-year 50-year 50-year Required Clearance 2-ft. 2-ft. 2-ft. Design Flood Frequency 50-year 50-year 50-year Designer Must Check Shoulder Break Point Clearance or Bridge Low Chord Clearance Required Clearance Design Flood Frequency 1-ft. below shoulder break point 1-ft. below shoulder break point 1-ft. below shoulder break point 100-year 100-year 100-year 1-ft. 5-year 2-ft. 1-ft. 10-year 2-ft. 1-ft. 25-year 2-ft. 1-ft. 50- 2-ft. year 1-ft. 25-year 2-ft. 1-ft. 10-year 2-ft. 1-ft. 50-year 2-ft. 5-year 10-year 25-year 50-year 25-year 10-year 50-year 1-ft. below shoulder break point 1-ft. below shoulder break point 1-ft. below shoulder break point 1-ft. below shoulder break point Shoulder break point not overtopped Shoulder break point not overtopped 1-ft. low-chord clearance 10-year 25-year 50-year 100-year 50-year 25-year 100-year 1-ft. 2-year 2-ft. 2-year 1-ft. 10-year 2-ft. 10-year Low-chord not overtopped Low-chord not overtopped 5-year 25-year GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-21 Refer to the most current version of the GDOT Manual on Drainage Design for Highways (also referred to as the Drainage Manual), which may be downloaded from the GDOT Repository for Online Access to Documentation and Standards (R.O.A.D.S.). For roadways, designers should be familiar with the concept of culvert hydraulics and be aware that head losses associated with culverts will generally produce a headwater greater than the design flood elevation of the natural conditions. A vertical profile that provides the prescribed clearances over either the headwater of the natural conditions or the headwater created by a culvert, whichever is greater, shall be developed. For bridges, designers should be familiar with the concept of riverine hydraulics and coordinate the bridge profile with the results of the bridge hydraulic study. As bridges will tend to generate backwater, a vertical profile that provides the prescribed clearances over the backwater created by the bridge or other nearby influencing structures shall be established. For additional information on Bridge Hydraulic guidelines, please refer to the GDOT Drainage Manual. 4.3.8. Reporting Changes in Vertical Clearances The GDOT Office of Maintenance (Maintenance Office) has the responsibility of providing the Office of Permits and Enforcement with the height limitation of structures. The Bridge Maintenance Office and the Office of Permits & Enforcement have the responsibility of approving the proposed routing on state routes for vehicle movements which are over the legal vertical clearance. It is extremely important for these offices to be kept informed of any change in vertical clearance as soon as possible after the change occurs. Persons (Area Engineer, Project Engineer) directly involved with vertical clearance revisions to any structure on a state route shall immediately notify: The GDOT Maintenance Office - Such a report should be made by telephone to the Routing Engineer at (404) 656-5287 or to the Assistant State Maintenance Engineer, Bridges. The Maintenance Office will handle the reporting of the above changes to the Office of Permits & Enforcement. The GDOT Bridge Maintenance & Inventory Office - This office should be notified of any changes in vertical clearances on the state system within 24 hours. In cases where the actual measured minimum vertical clearance must be revised, the person directly involved with the revision (Area Engineer, Project Engineer) shall advise the District Maintenance Office of the actual measured minimum vertical clearances on his/her specific construction project(s). The revised information should then be reported to the Bridge Inventory Office, and this information will be directed to local Bridge Inspection personnel, such that the revisions to the Bridge Information System may be verified at a later date. The Bridge Inventory Office in Atlanta will initiate revisions to the system with notification to units requiring the revised information. The actual measured minimum vertical clearance should be recorded at both edges of the pavement, the crown point (if present) and at the edges of paved shoulders (if present). In addition, measurements at any other restricting locations caused by the geometrics of the overhead structure or roadway should be recorded. Special attention should be paid to the effects of reconstruction at a restrictive location. For example, to resurface beneath a posted clearance without insuring a correction in posting misinforms the traveling public and thus creates a possible hazardous condition. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-22 4.4. Combined Horizontal and Vertical Alignments Horizontal and vertical alignments are permanent design elements that warrant thorough study. Horizontal and vertical alignments should not be designed independently, but should complement each other. Poorly designed combinations can negate the benefits and aggravate the deficiencies of each. A well-designed combination, in which horizontal and vertical alignments work in concert, increases highway usefulness and safety, encourages uniform speed, and improves appearance. 4.4.1. Aesthetic Considerations Coordination of the horizontal and vertical alignment can result in a highway that is visually pleasing. This can be achieved in several ways: A sharp horizontal curve should not be introduced at or near the low point of a sag vertical curve, which produces a distorted appearance. There should be a balance between curvature and grades. The use of steep grades to achieve long tangents and flat curves, or the use of excessive curvature to achieve flat grades, are considered poor design. A logical design is a compromise between the two conditions. Wherever feasible the roadway should "roll with" rather than "buck" the terrain. If possible, every effort should be made to line up points of vertical intersection (PVI's) with horizontal points of intersections (PI's) and to maintain consistency between the horizontal and vertical curve lengths. Vertical curvature superimposed on the horizontal curvature generally results in a more visually pleasing facility. Successive changes in profile not in combination with horizontal curvature may result in a series of dips not visible to the driver. If PVI's and PI's cannot be made to coincide, the horizontal curvature should "lead" the vertical curve and the horizontal curve should be slightly longer than the vertical curve in both directions. A balanced design which provides horizontal and vertical alignments in the middle range of values is preferable to allowing either horizontal or vertical to become extreme in order to optimize the other. Design the alignment to enhance attractive scenic views of the natural and manmade environment, such as rivers, rock formations, parks, and outstanding buildings. In residential areas, wherever possible, design the alignment to minimize nuisance factors to the neighborhood. Generally, a depressed facility makes a highway less visible and less noisy to adjacent residents. Minor horizontal adjustments can sometimes be made to increase the buffer zone between the highway and clusters of homes. Refer to the GDOT Context-Sensitive Design Online Manual , for additional information. 4.4.2. Safety Considerations The superimposed effect of horizontal and vertical alignments can influence both sight distance and driver expectancy which translate directly into safety. As safety should be the designer's primary consideration, the following guidelines are presented: Sharp horizontal curves should not be introduced at or near the top of a pronounced vertical curve, since the driver cannot perceive the horizontal change in alignment, especially at night. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-23 Sharp horizontal curves should not be introduced at or near the low point of a sag vertical curve, since vehicles, particularly trucks, are traveling faster at the bottom of grades. Both horizontal and vertical curvature should be as flat as possible at intersections where vehicles have to decelerate, stop, or accelerate. To maintain proper pavement drainage, design vertical and horizontal curves so that the flat profile of a vertical curve will not be located near the flat cross slope of the superelevation transition. As a general rule, pavement cross slope should be at least 1.0% near vertical curve sag points and longitudinal roadway grades should be at least 0.30% at locations where the pavement cross slope is flat (0%), for instance at superelevation transitions. On two-lane roadways, the need for safe passing sections (at frequent intervals and for an appreciable percentage of the length of the roadway) often supersedes the general desirability for combination of horizontal and vertical alignment. The Designer should strive to implement long tangent sections to secure sufficient passing sight distance. It is generally poor practice to place the superelevation rotation point at a different point than the profile grade line. Particular attention shall be paid to all forms of sight distance when horizontal and vertical alignments are superimposed on each other. The combination of horizontal and vertical curvature can sometimes result in effectively less sight distance than the individual affect of either horizontal or vertical curvature. 4.4.3. Divided Highways A well designed roadway will incorporate a litany of considerations including safety, economy, and aesthetics, etc. When terrain is hilly, mountainous or undulating, the profile of the roadway should generally follow the contours of the land (barring overriding considerations). On divided highways and rural interstates, the Designer should recognize where terrain dictates, separate horizontal alignments and vertical profiles can be utilized for opposing traffic. Independent Profiles and Increasing Median Width On state and federal divided highways, an increase in the width of the median and the use of independent alignments to derive the design and operational advantages of one-way roadways should be considered. Where right of way is available, a superior design, without significant additional costs, can result from the use of independent alignments and profiles. Bifurcated medians are especially effective where the general fall of the terrain is significant and perpendicular to the roadway. Increasing the width of the median and/or bifurcating the roadway should be considered in the following situations: Where right of way is available and where the general fall of the terrain is significant and perpendicular to the roadway In isolated areas on rural reconstruction projects where the height of vertical reconstruction is significant. This will facilitate efficiency and ease conflicts during an intermediate stage of construction. As a general rule of thumb, standard 44-ft. median width can be maintained with independent profiles until the difference in elevations in opposing PGL's is approximately 5-ft. Consideration should be given to increasing the median width (beyond 44-ft.) a minimum of 2-ft. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-24 for every 1-ft. of vertical profile reconstruction greater than 5-ft. Obviously, increasing the median width will result in greater right of way impacts. However, in many instances, minor right of way impacts - especially in rural areas where it is plentiful are ultimately less costly than significant vertical reconstructions that require the contractor to utilize earth stabilization techniques or sheet pile to construct. At intersections to eliminate breakovers. 4.5. Superelevation When a vehicle travels around a horizontal curve, it is forced radially outward by centrifugal force. When this force becomes too great for a given design speed, the roadway is "superelevated" to counter it. Five methods of counteracting centrifugal forces through curves are discussed in the AASHTO Green Book Chapter 3, Elements of Design. 4.5.1. Maximum Superelevation Rates "Superelevation" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the Superelevation rates shown in table 4.9 as the standard for superelevation rates in Georgia. The FHWA has stated that a Design Exception is required if the State's superelevation rate cannot met. Therefore, a decision to use a Superelevation rate that does not meet the maximum Superelevation Rate shown in Table 4.9 shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the Department's Chief Engineer. Horizontal alignments are composed of tangent sections connected by arcs of circular curves (GDOT does not normally use spiral curves). Vehicles traveling in a circular path counter the centrifugal force that would cause them to leave the road through a combination of two factors: lateral friction between the vehicle's tires and the road, and superelevation. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-25 The maximum rates of superelevation used on highways are controlled by four factors: Climatic conditions (i.e., frequency and amount of snow and ice) Terrain conditions (i.e., flat, rolling, or mountainous) Type of area (i.e., rural or urban) Table 4.9. Maximum Superelevation Rates Setting Maximum Superelevation Rates (emax)(1) Urban (Curb and Gutter) Roads (DS < 45mph) 4% Suburban / Developing Areas 6% Frequency of very slow-moving vehicles whose operation might be affected by high superelevation rates Rural (Non Curb and Gutter) Paved Roads Unpaved Roads 6% Reverse Crown Interstates, Expressways, Superelevation requirements for maximum L/A Facilities superelevation rates (0.04 to 0.12-ft./ft) for various Rural 8% design speeds (15 mph to 80 mph) are provided in Urban 6% the AASHTO Green Book Chapter 3, Elements of Design Superelevation Tables. GDOT has designated the values in Table 4.9. as the System-to-System Ramps Rural 8% maximum values (emax) for use on Georgia roadways. Urban Exit-Entrance Ramps 6% 8% Free Flowing Loop Ramps 10% It is important for designers to realize that the minimum curve radii and maximum superelevation rates depicted in the AASHTO Green Book are extremes and should be avoided wherever possible. Long Ramps with STOP 8% (1) The maximum allowed values (emax) for usage on Georgia roadways, as designated by GDOT. In general, GDOT does not require superelevation on lowspeed urban roadways or roadways with a design speed of 25 mph or less The emax values presented in Table 4.9. requires the use of the more moderate design value ranges for curvature and superelevation. In certain situations, such as those described below, the emax values in Table 4.9. may require further reduction: Wherever practical, consideration should be given to maximizing curve radii and minimizing superelevation rates on curves which include bridges. This is due to the increased potential for icing. Where constraints do not exist, an emax of 4% should be utilized. Wherever possible, the maximum superelevation rates on roadways within an intersection should be limited to 4% (2% for urban areas with crosswalks). Wherever possible and when applicable in intersections, superelevation cross slopes of one roadway should be coordinated with the mainline profile grade of the intersecting roadway. Where traffic congestion or extensive development acts to restrict top speeds on a rural roadway, a maximum rate of superelevation of 6% should be used. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-26 4.5.2. Sharpest Curve without Superelevation Although superelevation is advantageous for high-speed traffic operations, various factors combine to make its use impractical in many built-up areas. Such factors include: wide pavement areas need to meet grade of adjacent property surface drainage considerations frequency of cross streets, alleys and driveways at major intersections or other locations where there is a tendency to drive slowly because of turning and crossing movements, warning devices, and traffic signals The minimum curve radius is a limiting value of curvature for a given design speed and is determined from the maximum rate of superelevation and the maximum side friction factor selected for design. Very flat curves need no superelevation. In many instances, it is desirable to maintain a normal crown typical section on the roadway. In these cases, implementation of a curve with a radius flat enough as to not require superelevation should be considered. 4.5.3. Axis of Rotation Roadway alignments are generally defined by a centerline (CL) and a profile grade line (PGL). The roadway may be rotated about various points on the typical section to achieve superelevation. Typically, the point of superelevation rotation (axis of rotation) corresponds to the PGL located on the inside edges of the travel lanes. On two-way roadways with a flush, raised or no median, the axis of rotation typically corresponds to the roadway centerline. Generally, rotation will occur about the centerline on roadways with an urban typical section. In most instances, the axis of rotation, the PGL or centerline and the pavement crown line are the same although it is not mandatory. The following represent GDOT guidelines when establishing the location of the superelevation rotation point: For almost all situations involving two-lane, three-lane and four-lane (with raised median) typical sections, the axis of rotation is located on the centerline of the proposed pavement. One exception to this is three-lane section which is widened to one side from two-lane sections. In this case, the axis of rotation typically follows the location of the former centerline of two-lane pavement. The actual point of rotation with a raised median is an imaginary point which is developed by projecting the left and right pavement cross slopes respectively and intersecting them with the project centerline to form a common point. In four-lane and six-lane typical sections involving depressed medians, the axis of rotation generally follows the inside edge of the inside travel lane (Lane 1). This approach facilitates consistent median drainage but can create drainage problems near median breaks. Particular attention should be paid to pavement drainage in the areas near median breaks and should examine the pavement profile of the median break crossover. A point of rotation at the centerline where depressed medians are in urban areas or where there is a potential for future development and the addition of future crossovers should be considered. In areas where superelevation rates would create median slopes greater than 4:1 it will be necessary to use split rotation points. When the median width is 44-ft. this typically occurs when the superelevation rate exceeds 5%. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-27 In a six-lane or 8-lane typical section involving a concrete median barrier, the axis of rotation will follow the lane line separating Lane 1 from Lane 2. In typical sections which involve more than three-lanes in each direction, the profile grade line (crown point or axis of rotation) will generally begin to move from its standard location on the inside edge of the inside travel lane towards the outside in one-lane increments. This is due to the need to balance pavement drainage and to maintain practical superelevation transition and tangent runout lengths. There should never be more than a three-lane difference between the number of lanes on one side of the pavement "crown" vs. the other side. Table 4.10. Superelevation Rotation Points and Rotation Widths, summarizes the location of the axis of rotation for various typical sections utilized by GDOT. For further information or more detail regarding typical sections, refer to Chapter 6 of this Manual or consult the typical section cells associated with the GDOT Electronic Data Guidelines. 4.5.4. Superelevation Transitions Development of Superelevation For appearance and comfort, the length of superelevation runoff (and tangent runout) should be based on a relative gradient between the longitudinal grades of the axis of rotation and the outside edge of traveled way pavement. The maximum relative gradient is varied with design speed to provide longer runoff lengths at higher speeds and shorter lengths at lower speeds. The maximum relative gradients are depicted in Table 4.11. Maximum Relative Gradients. These values correspond to those found in the AASHTO Green Book. Refer to the AASHTO Green Book for guidance on establishing superelevation runoff lengths, superelevation (tangent) runout lengths and locating superelevation transitions. AASHTO guidelines shall be followed when determining and locating superelevation runoff, runout and transitions. When AASHTO values cannot be attained for superelevation parameters, a design exception is required. GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-28 Table 4.10. Superelevation Rotation Points and Rotation Widths Barrier Inside Barrier Outside Symmetric Widening Asymmetric Widening New Location Reconstruction No. of Lanes Median Width (ft.) Median Type Horizontal Location of Rotation Point Rotation Width (ft.) Urban Typical Section 2 0 3 14 3 14 5 14 4 20 6 20 4 24 6 24 N/A Flush Flush Flush Raised Raised Raised Raised Rural Typical Section 2 0 N/A 3 14 Flush 3 14 Flush 5 14 Flush 4 20 Raised 6 20 Raised 4 24 Raised 6 24 Raised 4 32 Depressed 6 32 Depressed 4 44 Depressed 6 44 Depressed Ramp Typical Section 1* 0 N/A 2* 0 N/A 1* 0 N/A 2* 0 N/A Limited Access Typical Section 1* 0 N/A 2* 0 N/A 3* 0 N/A 4* 0 N/A Hybrid Typical Section 2 44 Depressed 3 44 Depressed 4 44 Depressed 2 52 Depressed 3 52 Depressed 4 52 Depressed 2 64 Depressed 3 64 Depressed 4 64 Depressed X X X X X X X X X X X X X X X X X X XX X XX X XX X XX X XX X XX X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X CL of pavement CL of new pavement CL of old pavement CL CL CL CL CL CL of pavement CL of new pavement CL of old pavement CL of pavement CL of pavement CL of pavement Inside of TL 1 Inside of TL 1 Inside of TL 1 TL 1 Inside of TL 1 TL 1 Outside edge of TL Outside edge of TL 2 Outside edge of TL Outside edge of TL 2 Inside of TL 1 Inside of TL 1 Varies Varies Inside of TL 1 Inside of TL 1 Between TL 1 and TL 2 Inside of TL 1 Inside of TL 1 Between TL 1 and TL 2 Inside of TL 1 Inside of TL 1 Between TL 1 and TL 2 3 28 Flush w/ Barrier X X X X X Between TL 1 and TL 2 4 28 Flush w/ Barrier X X X X X Between TL 1 and TL 2 5 28 Flush w/ Barrier X X X X X Between TL 2 and TL 3 3 32 Flush w/ Barrier X X X X X Between TL 1 and TL 2 4 32 Flush w/ Barrier X X X X X Between TL 1 and TL 2 5 32 Flush w/ Barrier X X X X X Between TL 2 and TL 3 3 40 Flush w/ Barrier X X X X X Between TL 1 and TL 2 4 40 Flush w/ Barrier X X X X X Between TL 1 and TL 2 5 40 Flush w/ Barrier X X X X X Between TL 2 and TL 3 * One-Way Notes: 1. Outside Typical Sections 2. Assume 12-ft. Lane Widths 3. On raised medians, PGL is located by projecting Symbols: CL = Centerline pavement cross slope to the centerline TL = Travel Lane GDOT Design Policy Manual Revised 09/03/10 Elements of Design 12 19 26 31 34 46 36 48 12 19 26 31 34 46 36 48 24 24 - 16 24 16 24 12 24 - 24 36 36 24 36 36 24 36 36 24 36 36 24 36 36 24 36 36 4-29 Table 4.11. Maximum Relative Gradients indicates that relative gradients vary per design speed. A strict application of the maximum relative gradient criterion provides runoff lengths for four-lane undivided roadways that are double those for two-lane roadways; and those for six-lane undivided roadways would be tripled. While lengths of this order may be desirable, it is often not practical to provide such lengths in design. It is recommended that minimum superelevation runoff lengths be adjusted downward to avoid excessive lengths for multilane highways. The recommended adjustment factors are presented in Table 4.12. Adjustment Factor for Number of Rotated Lanes. These values correspond with the values found in the AASHTO Green Book (2004). To calculate minimum superelevation runoff length, use the equation: L (wN1) G e d * (bw ) Table 4.11. Maximum Relative Gradients Design Speed (mph) 14 20 25 30 35 40 45 50 55 60 65 70 75 80 Maximum Relative Gradient, G (%) 0.78 0.74 0.70 0.66 0.62 0.58 0.54 0.50 0.47 0.45 0.43 0.40 0.38 0.35 Equivalent Maximum Relative Slope 1:128 1:135 1:143 1:152 1:161 1:172 1:185 1:200 1:213 1:222 1:233 1:250 1:263 1:286 where: L = minimum length of superelevation runoff (ft.) G = maximum relative gradient (%) N = number of lanes rotated (on one side of 1 axis of rotation, not total number lanes) b = adjustment factor for number of lanes w rotated w = width of one traffic lane (usually 12-ft.) e = design superelevation rate (%) d For example, assume a five-lane roadway (12-ft. lanes) with 0.06 (6%) superelevation and 45 mph design speed. In the equation above, G = 0.54, N = 2.5, b = 1 w 0.7, w = 12, and e = 6.0. Inserting these numbers into the equation gives: Table 4.12. Adjustment Factor for Number of Rotated Lanes Number of Lanes Rotated (N1) Adjustment Factor (bw) Length Increase Relative to 1 Lane Rotated (=N1bw) 1.00 1.00 1.00 1.50 0.83 1.25 2.00 0.75 1.50 2.50 0.70 1.75 3.00 0.67 2.00 3.50 0.64 2.25 Source: AASHTO. (2004). Green Book. L (12)(2.5)(6) * (0.7) 233.33 ft. 0.54 GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-30 Minimum Length of Superelevation Runoff There are a number of rational approaches to transitioning from a normal crown section to a superelevated section. Wherever possible, GDOT applies 2/3 of the superelevation runoff outside the curve and 1/3 of the superelevation runoff inside the curve. For the above example, the amount of superelevation applied outside the curve would be (2/3)(233.33) = 155.56-ft. and the amount of superelevation applied inside the curve would be (1/3)(233.33) = 77.78-ft. Tangent runout is the length required to transition from a normal crown to a flat section on the outside of a horizontal curve. The tangent runout length is determined in the same manner as the superelevation runoff length. For the example above, assuming a normal crown cross slope of 2%), the tangent runout length would be: L (12)(2.5)(2) * (0.7) 77.78 ft. length tangent runout 0.54 Calculated lengths may be rounded to the nearest foot, if desired. If geometric constraints exist, consideration may be given to placing 50% of the superelevation runoff on the tangent and 50% of the runoff on the curve. Sometimes, conditions exist where it is not possible to develop the desirable amount of runoff (or runout) and it is impossible to locate the transition in the ideal location relative to the curve PC or PT. Examples of this include: Reverse curves (especially prevalent in mountainous regions) Broken back curves Approaches to intersections These undesirable situations should be avoided, wherever feasible. However, since these instances are sometimes unavoidable (or the desirable implementation is impractical) professional judgment should be exercised when determining less-than-ideal transition rates and transition locations. Some practical guidelines for handling these situations include: For a symmetric (equal radius) reverse curve, place the 0% cross slope point at the PT and PC common to both curves For asymmetric reverse curves (of different radii), attempt to place the superelevation transition in a location which is proportional to the e of the two curves max For broken back curves, attempt to place the average e cross slope at the center of the max tangent Pavement warping near intersection tie-ins is sometimes required (e.g. when there are superelevation transitions near intersections, ADA requirements, drainage, sight distance, and operations which should be taken into consideration) GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-31 Figure 4.1., Crowned Traveled Way Revolved About Centerline, illustrates the development of tangent runout and superelevation runoff for a roadway with the profile control and superelevation rotation point at the center of the roadway. Figure 4.1. Crowned Traveled Way Revolved About Centerline GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-32 Chapter 4 Index ADA Requirements, 17 Alignment Aesthetic Considerations, 24 Combined Horizontal and Vertical, 2426 Divided Highways, 25 Horizontal, 414 Vertical, 1423 Broken Back Curves. See Curves Horizontal Circular Curves. See Curves - Horizontal Compound Curves. See Curves - Horizontal Curves - Horizontal Broken Back Curves, 7 Circular Curves, 6 Compound Curves, 6 Minimum Length, 8 Reverse Curves, 6 Sight Distance on, 1 Spiral Curves, 4, 7 Curves - Vertical, 20 Decision Sight Distance. See Sight Distance: Decision Sight Distance Horizontal Alignment. See Alignment, Horizontal Interchanges Ramps, 6 Intersection Sight Distance. See Sight Distance: Intersection Sight Distance Intersections Angle, 3 T-Intersection, 3 Passing Sight Distance. See Sight Distance: Passing Sight Distance Reverse Curves. See Curves - Reverse Right of Way Intersections, 4 Safety, 2425 Sight Distance Decision Sight Distance, 2 General Considerations, 1 Intersection Sight Distance, 2 Passing Sight Distance, 2, 5 Stopping Sight Distance, 1 Spiral Curves. See Curves - Horizontal Stopping Sight Distance. See Sight Distance: Stopping Sight Distance Superelevation, 6, 10, 13, 16, 18, 25, 28, 2633 Vertical Alignment. See Alignment, Vertical Vertical Curves. See Curves - Vertical Vertical Grades, 18 GDOT Design Policy Manual Revised 09/03/10 Elements of Design 4-33 Chapter 5 Contents 5. ROADSIDE SAFETY AND LATERAL OFFSET TO OBSTRUCTION 1 5.1. General Considerations 1 5.2. Rural Shoulder Lateral Offset to Obstruction 2 5.3. Urban Shoulder Lateral Offset to Obstruction 3 5.4. Lateral Offsets for Signs 4 5.4.1. Sign Placement 4 5.4.2. Sign Supports 4 5.5. Lateral Offsets for Light Standards 4 5.5.1. High Mast Roadway Lighting 4 5.5.2. Roadway Lighting 4 5.5.3. Pedestrian lighting (non-roadway) 5 5.6. Lateral Offsets for Utility Installations 5 5.6.1. General Guidance 5 5.6.2. Rural Shoulders 5 5.6.3 Urban Shoulders 5 5.7. Lateral Offsets for Signal Poles and Controller Cabinets for Signals 6 5.7.1. Rural Shoulders 6 5.7.2. Urban Shoulders 6 5.8. Lateral Offsets to Trees and Shrubs 6 5.8.1. Rural Shoulders 6 5.8.2. Urban Shoulders 6 List of Tables Table 5.1 Minimum Lateral Offsets for Utility Installations: Rural Shoulders 5 Table 5.2 Minimum Lateral Offsets for Utility Installations: Urban Shoulders 5 Table 5.3 Minimum Lateral Offsets to Trees and Shrubs: Urban Shoulders 6 GDOT Design Policy Manual Revised 02/22/2011 Chapter 5 Contents i 5. ROADSIDE SAFETY AND LATERAL OFFSET TO OBSTRUCTION 5.1. General Considerations "Lateral Offset to Obstruction" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for minimum "lateral offset to obstruction" for roadway classifications in Georgia. A decision to use an offset value that does not meet the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the GDOT Chief Engineer. In addition, GDOT has developed, as standard practice, the following more specific and selective criteria on "lateral offset to obstruction" for signs, light standards, utility poles, signal poles and controller cabinets, and trees and shrubs. A decision to use an offset value that does not meet the criteria defined by GDOT shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the Chief Engineer. It is the goal of the Georgia Department of Transportation (GDOT) to provide and maintain a high quality statewide multimodal transportation system. Addressing roadside safety is key to achieving this goal. Promoting effective relationships with stakeholders is also a GDOT goal. Often, input from stakeholders regarding roadside amenities and design requires a proactive and ongoing coordination effort with stakeholders to achieve success. While these two goals may at times seem to be in competition with one another, it is important to recognize that each goal contributes to GDOTs ability to achieve its mission of providing a safe transportation system that is sensitive to the needs of its citizens and environment. Features and elements generally encountered in roadside design for new construction or reconstruction projects are identified in respective sections of this chapter. Therefore, this chapter addresses the area outside of the actual traveled way which is also an important component of roadway design. Under certain circumstances, the policies described in this chapter may not be applicable to permitting on existing facilities or temporary conditions and facilities. The GDOT standard minimum lateral offsets to obstructions are listed later in this chapter. However, the reader is cautioned that the offsets alone do not present a complete solution to allow features or objects on the shoulder or roadside. GDOT strongly discourages arbitrary reduction of design speed in order to reduce offset requirements. Sound engineering judgment and reasonable environmental flexibility should be exercised in selecting and specifying roadside features at each location. "Roadside" is defined in the American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide as the area between the outside shoulder edge and the right-of-way limits. In curb and gutter sections, the roadside includes the urban shoulder, which is part of an urban roadway that begins at the edge of traveled way and extends to the right-of-way limit or to the breakpoint of the fore slope or back slope that ties to the natural terrain. GDOT Design Policy Manual Revised 02/22/2011 Roadside Safety and Lateral Offset to Obstruction 5-1 The following elements should, at a minimum, be considered by the designer, even when compliance with established offsets is proposed: current traffic volumes; design year traffic volumes (for projects under design); truck percentages; current detailed crash history; posted speed limit; design speed (if available); operating speed (85th percentile, off peak); functional classification of the roadway; roadway setting/context (urban environment, rural, residential, commercial, historic district, etc.) and if the proposed project fits in with the roadway setting/context; existing operations (e.g. sight distance or vehicular operations), and the proposed projects affect on those operations; maintenance; existing roadside elements (e.g. permitted utilities or lighting) impacted/affected by the proposed project; proposed roadside elements and their consistency with the needs of the corridor (e.g. safety, utility, and aesthetic needs for pedestrian, bicycle, transit, vehicular traffic; consistency needs in terms of conformity with local, regional, and state roadside amenity values); and mitigation measures that should be considered (including the removal or relocation of fixed objects, the reduction of impact severity by implementing breakaway or traversable features, and the shielding of fixed objects with traffic barriers such as guardrail). 5.2. Rural Shoulder Lateral Offset to Obstruction Lateral Offset to Obstruction is the horizontal distance measured from the edge of the traveled way, to the face of a roadside object or feature. The rural shoulder is the part of the roadway beyond the edge of traveled way that is graded or paved flush with the edge of traveled way to allow for emergency usage. Lateral Offset to Obstruction for rural type shoulders, including graded or paved surfaces, is based on the concept of clear zone that is established by the AASHTO Roadside Design Guide. By definition, clear zone is the area beyond the roadway edge of traveled way which provides an environment free of fixed objects, with stable, flattened slopes which enhance the opportunity for vehicle recovery and/or reducing crash severity (AASHTO, 2006). Fixed objects include trees, large shrubs, bodies of water, and elements of the roadway facility such as road signs, structure piers, utility poles or light standards, and electrical or controller cabinets, or other non-moveable objects that can pose a safety hazard to a vehicle and its occupants if the vehicle leaves the roadway. In determining the acceptable clear zone for a particular roadway and prevailing conditions, refer to the current AASHTO Roadside Design Guide in its entirety, and not just to the tables provided in Chapter 3 of the Guide. Principles of clear zone include safe drainage structure end treatments, ditch design, curve correction factors, and many other features that are key elements to the overall safe and aesthetically pleasing roadside design. It is not the intent of this Manual to reproduce the clear zone values that are provided in the AASHTO Roadside Design Guide. GDOT Design Policy Manual Revised 02/22/2011 Roadside Safety and Lateral Offset to Obstruction 5-2 The designer should provide the maximum clear zone that is commensurate and practical for the prevailing conditions. The maximum clear zone values, based on the traffic volume, slope, geometry and design speeds identified in the current AASHTO Roadside Design Guide should be utilized on new construction or when providing full reconstruction of the roadway. If not practical to provide the recommended upper value due to overall highway design considerations, the minimum values shall be observed, for the respective conditions. For retro-fit types of projects, achieving the minimum clear zone values are acceptable. Features or objects located within the accepted clear zone for a roadside should comply with the guidelines provided in the AASHTO Roadside Design Guide. If features or fixed objects cannot be removed or modified to become clear zone compliant, they shall be shielded in a cost effective manner that is consistent with current practice and standards. It is GDOTs policy that fixed objects in median areas of 64-ft or less that cannot be eliminated shall be treated with cost-effective shielding devices, such as guardrail, impact attenuators, or earth-mound redirection design. In cases where road median widths are greater than 64-ft, but less than 84-ft, specific engineering judgment should be made by the designer. For medians wider than 84-ft, it is not necessary to protect fixed objects that are located near the center of the median and outside the required clear zone. For roadsides, it is GDOTs policy to shield objects that are within the defined clear zone. The intent of the designer should be to reduce the seriousness of the consequences of a vehicle leaving the roadway. 5.3. Urban Shoulder Lateral Offset to Obstruction Lateral Offset to Obstruction on urban roadways is not based entirely on the clear zone concept due to various pre-existing conditions and urban roadway shoulder constraints, although clear zone considerations may apply under certain conditions, such as run-off-road (ROR) crash history, excessive volumes, geometric conditions, excessive operating speeds, new location construction, etc. Urban roadways are generally confined on the roadside and are posted at speeds of 45 mph or less. According to the AASHTO Roadside Design Guide, the presence of curb and gutter within the roadside, even barrier-faced, does not generally redirect a vehicle, especially at speeds above 25 mph. Lateral Offsets to Obstructions for urban roadways is based on the specific feature or element being considered, and generally is related to a combination of environmental, operational and safety characteristics, both for pedestrians and vehicular traffic. According to the AASHTO Roadside Design Guide, Chapter 10, Roadside Safety in Urban or Restricted Environments, uniform lateral offsets between traffic and roadside features is desirable (2006). It is GDOTs intent to facilitate this principle as much as practical, using this design policy manual, ongoing education and collaboration with GDOT staff and participating stakeholders. The GDOT Pedestrian and Streetscape Guide written and maintained by the GDOT Office of Planning, has direct application on urban shoulder usage. The GDOT Pedestrian and Streetscape Guide provides guidance for design professionals, developers, municipalities and others regarding the design, construction, and maintenance of pedestrian facilities. The GDOT Office of Utilities employs the GDOT Utility Accommodation Policy and Standards Manual to guide decisions for utility facility placement on public right-of-ways. Both rural and urban conditions are addressed in this document. The lateral offset of 1-ft, 6 in. from face of curb to face of fixed object stated in the AASHTO Green Book shall be an absolute minimum lateral offset for urban roadways. Lateral offsets less than 1-ft, 6 in. shall require a design exception. GDOT Design Policy Manual Revised 02/22/2011 Roadside Safety and Lateral Offset to Obstruction 5-3 5.4. Lateral Offsets for Signs 5.4.1. Sign Placement Placement of traffic control, informational, or any other types of signs that are allowed on the road right-of-way shall be in accordance with the most current edition of the Federal Highway Administration (FHWA) Manual of Uniform Traffic Control Devices, (MUTCD), and with practices and policies of the GDOT Office of Traffic Operations. Obstruction of sidewalks should be avoided in reconstruction projects. However, encroachments of sign placements in sidewalks, if necessary as a retrofit, shall ensure that an unobstructed, ADAcompliant sidewalk is provided. 5.4.2. Sign Supports Sign supports, except for overhead sign supports, shall be frangible or breakaway in rural or urban shoulder environments. If the support is located outside the accepted clear zone for the roadway, frangible or breakaway design is not required. If overhead sign supports are required within the accepted clear zone for the prevailing rural condition, the support shall be shielded with barrier or guardrail. Overhead sign supports in urban roadways should observe the same lateral offset requirements as utility installations in urban roadways. However, if this is not practical, the minimum lateral offset from the face of curb to the face of the support is 6-ft. 5.5. Lateral Offsets for Light Standards 5.5.1. High Mast Roadway Lighting High mast lighting should be positioned outside the clear zone. If this is impractical, cost-effective shielding shall be provided in accordance with current standards for roadside barrier. 5.5.2. Roadway Lighting Roadway lighting should be placed on or along the outside shoulders as described below. The size of the base must be considered when measuring lateral offset. Breakaway or frangible bases are generally wider than the pole. Rural Shoulders Light standards should be mounted outside the clear zone. Any light standards that are not located outside of the clear zone should be mounted on an AASHTO compliant breakaway mounting, or be appropriately shielded. Urban Shoulders In urban roadway conditions, light standards should be positioned in accordance with rural shoulder guidelines or as close to the right-of-way limit as possible. If it is not feasible to comply with the above statement, light standards shall be placed directly outside of the sidewalk and at least 6-ft from the face of curb. Coordination of street light placement with sidewalks and other roadside features shall ensure that at least 4-ft of usable sidewalk remains, and that the lights do not conflict with other permitted features or elements on the urban shoulder. GDOT Design Policy Manual Revised 02/22/2011 Roadside Safety and Lateral Offset to Obstruction 5-4 Normally, a breakaway mounting design should be used for urban shoulders. However, breakaway type designs should not be used on streets in densely developed, low speed, urban areas where high pedestrian volumes would be expected. 5.5.3. Pedestrian lighting (non-roadway) All pedestrian light standards should be located at the back of the sidewalk. If sidewalk is not present, the light standards should be placed a minimum of 6-ft from the face of curb. 5.6. Lateral Offsets for Utility Installations 5.6.1. General Guidance Utility installations are governed by the GDOT Utility Accommodation Policy and Standards Manual (UAPSM). Designers should read and understand the referenced policy, in conjunction with the policies and guidelines set forth in this Manual. 5.6.2. Rural Shoulders Refer to Table 5.1. for GDOT minimum lateral offsets to utility installations on roadways with rural shoulders. Table 5.1 Minimum Lateral Offsets to Utility Installations: Rural Shoulders Posted Speeds Slope Condition GDOT Policy < 60 mph fill section with slopes 4:1 or flatter Utility obstacles shall be located at least 30-ft from the edge of traveled way to the face of the obstacle < 60 mph fill section with slopes steeper than 4:1 The horizontal distance in which slopes steeper than 4:1 are encountered is not to be considered as ,,traversable and recoverable. Consult the AASHTO Roadside Design Guide and the UAPSM for full understanding. > 60 mph all slope conditions Utility obstacle shall be located outside the accepted clear zone for the prevailing conditions, or 30-ft, whichever is greater. 5.6.3 Urban Shoulders Utility obstacles should be positioned as near as possible to the right-of-way or utility easement. Utility obstacles should be placed in keeping with the nature and extent of roadside development. Lateral offsets to utility obstacles is measured from the face of curb to the face of pole or obstacle. Table 5.2 Minimum Lateral Offsets to Utility Installations: Urban Shoulders Posted Speeds Minimum Lateral Offsets < 35 mph 6-ft No utility obstacle shall encroach on current sidewalk clearances required by ADA. > 35 mph and < 45 mph 8-ft For utility relocation on urban roadway projects, the utility offset shall be governed by design speed, ADT, = 45 mph 12-ft etc. The designer shall conform to the minimum lateral offsets listed in Table 5.2. GDOT Design Policy Manual Revised 02/22/2011 Roadside Safety and Lateral Offset to Obstruction 5-5 5.7. Lateral Offsets for Signal Poles and Controller Cabinets for Signals Lateral Offsets to signal poles and controller cabinets for signals are designated by the GDOT Office of Traffic Operations Traffic Signal Design Guidelines. 5.7.1. Rural Shoulders On roadways with rural shoulders, signal poles and controller cabinets for signals shall be located outside the clear zone. 5.7.2. Urban Shoulders The lateral offsets to signal poles and controller cabinets for signals shall be located a minimum of 6-ft from face of curb or behind sidewalk, whichever is greater. 5.8. Lateral Offsets to Trees and Shrubs Guidance on lateral offsets to trees and shrubs is provided from the GDOT Office of Maintenance, which also includes approvals through the Office of Traffic Operations. Additional guidance is provided by the Office of Planning through the GDOT Pedestrian and Streetscape Guide. Utilities and intersection sight distance requirements may affect the location and diameter size of proposed trees in the lateral offsets and clear zone. Clear zone requirements can be found in the current AASHTO Roadside Design Guide or in Chapter 4 of the current GDOT Regulations for Driveway and Encroachment Control. The roadways design speed shall be used to determine lateral offset to obstruction criteria. 5.8.1. Rural Shoulders On roadways with rural shoulders, trees and shrubs shall be located outside the clear zone. 5.8.2. Urban Shoulders On roadways with urban shoulders with a posted design speed of greater than 45 mph, trees and shrubs shall be located outside of the clear zone. On roadways with urban shoulders with a posted design speed of 45 mph or less, refer to Table 5.3. for minimum lateral offsets for trees and shrubs. Table 5.3 Minimum Lateral Offsets to Trees and Shrubs: Urban Shoulders Posted / Design Speeds Minimum Horizontal Clearance(1) < 35 mph (Commercial Area(2)) < 35 mph 40 mph 4-ft 8-ft in median 8-ft 8-ft in median 10-ft 16-ft in median(3) 45 mph 14-ft 22-ft in median(3) > 45 mph Outside the clear zone (1) From center of tree to face of curb (2) In a central Business District and/or where commercial businesses are typically directly adjacent to the right-of-way. (3)Small trees and shrubs that mature at <4" in diameter may be planted a minimum of 8 feet from the face of the curb in medians adjacent to 40 to 45 mph speeds. Tree size is diameter of the tree maturity, measured at dbh (4.5 feet) above the base of the tree. Certain situations may require an increased lateral offset for additional safety considerations. For rural shoulders, trees should be placed outside the clear zone. For Interstates, trees should have a minimum lateral offset of at least 120% of the clear zone requirement. GDOT Design Policy Manual Revised 02/22/2011 Roadside Safety and Lateral Offset to Obstruction 5-6 Chapter 5 Index Lateral Offset, 17 General Considerations, 12 Light Poles, 45 Shoulder-Rural, 23, 4, 5, 6 Shoulder-Urban, 5, 6 Signs, 4 Traffic Signal Poles, 6 Trees and Shrubs, 6 Utilities, 56 Lighting High Mast, 4 Highway, 45 Safety Horizontal Clearance. See Lateral Offset Roadside General Considerations, 12 GDOT Design Policy Manual Revised 02/22/2011 Roadside Safety and Lateral Offset to Obstruction 5-7 Chapter 6 Contents 6. CROSS SECTION ELEMENTS 3 6.1. Lane Width 3 6.2. Pavement Type Selection 3 6.3. Cross Slope 3 6.4. Pavement Crowns 3 6.5. Shoulders 4 6.6. Side Slopes 5 6.7. Border Area (urban shoulder) 6 6.8. Bike Lanes 7 6.9. Curbs 7 6.9.1. Curb Types 7 6.9.2. Methods of Construction 8 6.9.3. Raised Median Noses 9 6.9.4. Raised Channelizing Islands 9 6.10. Sidewalks 9 6.11. Barriers 910 6.11.1. Barrier Types 10 6.11.2. Glare Screens 11 6.11.3. End Treatments 11 6.12. Medians 1112 6.12.1. Interstate Medians 12 6.12.2. Arterial Medians 12 6.12.3. Medians at Pedestrian Crossings 13 6.13. Parking Lanes 13 6.14. Summary of Design Criteria for Cross Section Elements 1314 GDOT Design Policy Revised 07/22/2011 Chapter 6 Contents i List of Figures Figure 6.1 Illustrates the dimensions of a 16-ft wide border area. 6 Figure 6.2. Illustration of Typical Dimensions for Urban Local Roadways 19 Figure 6.3. Illustration of Typical Dimensions for Rural Local Roadways 20 Figure 6.4 Illustration of Typical Dimensions for Collector and Arterial Roadways 21 Figure 6.5. Illustration of Typical Dimensions for Urban Freeway 22 Figure 6.6. Illustration of Typical Dimensions for Interchange Ramps 23 List of Tables Table 6.1. Rumble Strip Placement 5 Table 6.2. Curb Types Allowed for Various Types of Roads 8 Table 6.3. Median Options for Arterials (Including GRIP Corridors) 1213 Table 6.4. Design Criteria for Local Roadways 15 Table 6.5. Design Criteria for Collector Roadways 16 Table 6.6. Design Criteria for Arterial Roadways 17 Table 6.7. Design Criteria for Freeways 18 GDOT Design Policy Revised 07/22/2011 Chapter 6 Contents ii 6. CROSS SECTION ELEMENTS 6.1. Lane Width "Lane width" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for lane width options for roadway classifications in Georgia. The designer is encouraged to select a lane width that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a lane width value that does not meet the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the GDOT Chief Engineer. 6.2. Pavement Type Selection The designer should refer to the current GDOT Pavement Design Manual for guidance relating to the pavement type selection process. 6.3. Cross Slope "Cross slope" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, GDOT adopts the AASHTO Green Book criteria as the standard for cross slope options for roadway classifications in Georgia. The designer is encouraged to select a cross slope that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a cross slope value that does not meet the controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the GDOT Chief Engineer. Typical practice is to provide a 2% pavement cross-slope for travel lanes. On multi- lane roadways, no more than two adjacent lanes should be constructed at the same cross slope. The cross slope may be broken at 1% intervals not to exceed 4% on any lane. 6.4. Pavement Crowns There are four categories of pavement crowns: One-way Tangent Crown: A one-way tangent crown slopes downward from left to right as viewed by the driver. It is used for all roadways providing one-way traffic, except as noted in the following paragraphs. Two-way Tangent Crown: A two-way tangent crown has a high point in the middle of the roadway and slopes downward toward both edges. It is used for all roadways providing twoway traffic. For divided multi-lane highways, the pavement is sloped downward and away from the median centerline, or from the left or right edge line of the median lane on a five-lane section. Two-way Crown Converted to One-way Use: When an existing roadway with a two-way crown is converted from two-way to one-way use, the existing crown shape can remain. GDOT Design Policy Manual Revised 07/22/2011 6-3 However, if possible, leveling may be used to adjust cross-slope in order to obtain a constant cross-slope. Cross-over Crown Break: The cross-over crown break between main lanes is limited to an algebraic difference of 4% (0.04 ft/ft). This applies at the break point of a two-way crown. The algebraic difference between the main roadway cross-slope and shoulder cross-slope should not exceed 8% (0.08 ft/ft). 6.5. Shoulders "Shoulder width" has been identified as a "controlling criteria" that has substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. Therefore, the GDOT adopts the AASHTO Green Book criteria as the standard for shoulder width options for roadway classifications in Georgia. The designer is encouraged to elect a shoulder width that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a shoulder width value that does not meet the minimum controlling criteria defined by AASHTO shall require a comprehensive study by an engineer and the prior approval of a Design Exception from the GDOT Chief Engineer. AASHTO defines a shoulder as, "the portion of the roadway contiguous with the traveled way that accommodates stopped vehicles, emergency use, and lateral support of the subbase, base and surface courses." GDOT has adopted 10-ft as the typical overall shoulder width for higher volume and higher speed (>45 mph) collector and arterial roadways in Georgia. This is consistent with the AASHTO desirable criteria for normal shoulder width along high-type facilities (see AASHTO Green Book, Ch. 4, Cross Section Elements). For high speed freeways and interstates, GDOT has adopted 14-ft as the typical overall outside shoulder width with 12-ft paved adjacent to the traveled way, and 12-ft as the typical overall inside shoulder width with 10-ft wide paved adjacent to the traveled way. Interstate ramp shoulders should be 12-ft wide outside with 10-ft paved adjacent to the traveled way, and 8-ft wide inside with 4-ft paved adjacent to the traveled way. The typical shoulder cross-slope for total shoulder width and paved shoulder width established by GDOT is 6% for outside shoulders and 4% for shoulders within the median of a multilane roadway. This can vary depending on project specifics. For instance, on some projects the paved shoulder cross-slope matches the roadway cross-slope. On four-lane divided highways, the cross-slope on the median shoulder in tangent section is controlled by the cross-over crown restrictions described in Section 6.4 of this Manual. Similarly, the outside shoulder cross-slopes (the convex side of the curve) on superelevated roadways will be controlled by the cross-over crown restrictions. As a result, the slope will depend on the superelevation rate. On superelevated roadways, the inside shoulder will maintain its normal crown slope for superelevation rates equal to or less than the normal shoulder slope. For superelevation rates greater than the normal shoulder rate, the inside shoulder slope is the same as the superelevation rate of the roadway. For additional discussion of the superelevation, refer to Chapter 4 of this manual. GDOT Design Policy Manual Revised 07/22/2011 6-4 Rumble Strips should be used as follows (see Table 6.1 for placement): rumble strips are to be the milled-in type; dimensions - 16 inches width, 7 inches length, inch depth, 5 inches space between; skip pattern - 28-ft of rumble strips, 12-ft clear space. Table 6.1. Rumble Strip Placement Roadway Type Interstate / Freeway(1) Rumble Strip Placement Continuous Multi-Lane Rural Section (design speed >50 mph) Skip pattern Two-Lane Rural Section (>400 ADT & >50 mph) 2-ft Paved Shoulder No rumble strip 4-ft Paved Shoulder Skip pattern (1) Where bicycles are NOT allowed Refer to GDOT Construction Detail S-8 for drawings of 4-ft. and 6.5-ft. paved shoulders, each showing the placement of the rumble strips. A paved 6.5-ft. shoulder should be provided on all multi-lane divided roadways with rural shoulders to provide for bicycle accommodation. Under special circumstances, GDOT Construction Details T-19, T-23 and T-24 provide other applications for various rumble strip/rumble patch devices. 6.6. Side Slopes The AASHTO Roadside Design Guide specifies the maximum (steepest) side slope that should be used on a project in order to meet clear zone requirements. Where a range of slopes is given, the Designer should strive to provide as flat a slope as practical. All front slopes (foreslopes) should be 4:1 or flatter, and no steeper than 2:1. GDOT discourages the use of 2:1 front slopes with guardrail unless economic constraints (construction costs, right-ofway impacts, or environmental impacts) outweigh the practicality of a 4:1 front slope. GDOT prefers the use of 6:1 front slopes on ditch sections with design speeds 65 mph; however, 4:1 front slopes are allowed as long as clear zone requirements are met. A "barn roof" is a roadway side slope that begins with a shallow slope, and is followed by a steeper traversable slope to allow the embankment to tie into the existing ground quicker than the shallower slope would. This reduces the amount of embankment and right-of-way required to construct the roadway. Figure 3.2 of the Roadside Design Guide shows an acceptable barn roof configuration. This figure shows a recoverable slope followed by a steeper non-recoverable 3:1 slope. This design provides a traversable side slope from the roadway to the bottom of the embankment. Although a "barn roof" with a 2:1 side slope outside of the clear zone technically complies with clear zone requirements, vehicles leaving the roadway have a tendency to travel to the bottom of any slope, including recoverable slopes. For this reason, barn roof is generally not acceptable if the front slope includes a non-traversable 2:1 front slope. In addition to the safety benefits, in urban and residential areas, slopes 4:1 or flatter can be mowed easily with a lawnmower. Efforts to save trees and other items sometimes complicate this procedure, and each residential lot should be addressed separately. Configurations should result in both a pleasing appearance and an easily maintainable configuration. Refer to Chapter 5, Roadside Safety and Lateral Offset to Obstruction of this manual and the AASHTO Roadside Design Guide, Chapter 3 for further discussion about roadway side slopes. GDOT Design Policy Manual Revised 07/22/2011 6-5 6.7. Border Area (urban shoulder) Typically referred to as an "urban shoulder", the AASHTO Green Book (Ch.4, Pedestrian Facilities) defines "border area" as, "In suburban and urban locations, a border area generally separates the roadway from a community's homes and businesses. The main function of the border is to provide space for sidewalks...streetlights, fire hydrants, street hardware, and aesthetic vegetation and to serve as a buffer strip." GDOT defines the limits of the border area on urban type projects to be from the outside edge-ofpavement outward, and to include the gutter, the curb, the sidewalk and any space available for buffer and/or utilities. GDOT encourages the use of a 16-ft wide border area on urban type projects, where right-of-way permits. When a roadway has multiple driveways, a 16-ft wide border area provides the buffer space needed to construct a sidewalk at a consistent 6-ft offset from the back of curb and to align with the back of a standard driveway concrete valley gutter. If a 16-ft wide border area is not practical, then a border area 10-ft wide is acceptable. In all cases, the sidewalk design must comply with ADA regulations. See Section 9.5.1 Pedestrian Facility of this manual for design criteria relating to sidewalks and pedestrian facilities in Georgia. Figure 6.1 Illustrates the dimensions of a 16-ft wide border area. GDOT Design Policy Manual Revised 07/22/2011 6-6 6.8. Bike Lanes See Section 9.5.2 Bicycle Facility Design for design criteria relating to bicycle facilities in Georgia. 6.9. Curbs The type and location of curbs affects driver behavior and the safety and utility of a highway. Curbs serve any or all of the following purposes: drainage control; pavement edge delineation; right-of-way reduction; aesthetics; delineation of pedestrian walkways; reduction of maintenance operations; and assistance in orderly roadside development. The AASHTO Green Book states that vertical curbs should not be used along freeways or other high-speed (i.e., > 45 mph) roadways, but if a curb is needed, it should be of the sloping type. Where used for pavement drainage or to intercept runoff from the roadside, V-gutter (with appropriately spaced inlets) is prefered over sloped curb. For roadways with a design speed > 45 mph, sloped curb faces on outside shoulders should be offset to the back of paved shoulder. The width of the paved shoulder should be at least 10-ft. For multi-lane divided roadways with a design speed > 45 mph, sloped curb faces on inside shoulders should be offset at least 4-ft from the inside edge of travel lane. Curbs may be constructed by a variety of methods. Typical shapes and dimensions for various types of curbs, including curb and gutter, are shown in GDOT Construction Standards and Details Ga. Std. 9032B. The relationship of curb-to-guardrail is critical. If the curb is not properly located, the guardrail will not function as intended. Chapter 5 of the AASHTO Roadside Design Guide (2006) discusses the location of curb with respect to the face of the guardrail. For additional information, refer to GDOT Construction Standards and Details, Ga. Std. 4280. See also Section 6.11.1 of this manual. 6.9.1. Curb Types Sloped Curbs or Barrier Curbs Curb shapes are generally classified as either sloped or barrier curbs. The sloped curb has a flat sloping face. The barrier curb has a characteristic steep face. Generally, barrier curb is only used when sidewalks are provided and in the curb return of turnouts to intersecting streets. See Table 6.2 for proper use of curb. Concrete or Asphaltic Curbs Portland cement concrete is used for most curbs. Asphaltic curbs are limited primarily to header curbs in parking areas. Asphaltic curbs are also used to control runoff and erosion on high fills (>20-ft) with 2:1 side slopes or in guardrail sections along rural roadways. See GDOT Construction Standards and Details, Construction Detail S-4 for information regarding the placement of asphaltic curbs behind guardrail. GDOT Design Policy Manual Revised 07/22/2011 6-7 Table 6.2. Curb Types Allowed for Various Types of Roads Road Type Curb Type(1) Interstate Urban State Route Design Speed < 45 mph State Route Design Speed > 45 mph Other Off Roadway Classification Concrete Curb and Gutter Type 1 Type 2 Type 3 Type 4 Type 7 x x x x x x x x x x Concrete Header Curb Type 1 x Type 2 x x x Type 3 x Type 4 x Type 7 Type 8 x x x x x x x Raised Median Type 1 Type 2 x Type 7 x x x x Raised Island Type 1 Type 2 Type 7 x x x x V Gutter x x (1) Typical shapes and dimensions for various types of curbs, including curb and gutter, are shown in Ga. Std. 9032B. Four-inch sloped Type I curbs placed at the back of the usable shoulder may be used on high speed facilities. For curbs on roundabouts see Section 8.3.8 of this manual. 6.9.2. Methods of Construction Integral Curb For concrete pavements, integral curb is preferred to curb and gutter because of economy in initial construction and maintenance. With this method, the concrete curb is poured when the concrete slab for the roadway is still in a plastic state. This creates an integral bond between the roadway and the curb. An alternate, and more popular, method of construction is to place tie bars in the concrete of the roadway slab. Later, when the pavement has hardened, the curb is poured so that the tie bars hold the curb firmly in place on the roadway. Although not truly integral with the pavement, this curb is commonly referred to as integral/tied curb. The depth of integral/tied curb should match the depth of the roadway slab. Curb and Gutter Concrete curb and gutter, as shown in the GDOT Construction Standards and Details, Ga. Std. 9032B, is generally used with asphaltic concrete pavement. Under this method, both the curb and the gutter are poured together, but not at the same time as the roadway pavement. The GDOT standard curb and gutter width is 2.5-ft for both sloped and barrier type curb and gutter. Where curb and gutter is placed adjacent to concrete pavement on curbed sections, tie bars should be GDOT Design Policy Manual Revised 07/22/2011 6-8 used to connect the curb and gutter to the adjacent pavement. This prevents separation of the curb and gutter from the edge of the pavement. Under restrictive right-of-way conditions, a 2-ft wide curb and gutter (6-inch curb, 18-inch gutter) may be used on local streets and state routes in Georgia, as shown in the GDOT Construction Standards and Details, GA. Std. 9032C. The designer should note that reducing the gutter width by 6-inches will reduce the hydraulic gutter capacity along the roadway and thus possibly increase the amount of drainage structures required to control an acceptable gutter spread for the design storm event. In addition, a reduced gutter width will require deeper Drop Inlet structures (Ga. Std. 1019C). Therefore, the decision to use a 2-ft wide curb and gutter will require an engineering study and approval by the State Design Policy Engineer/Hydraulics Engineering Group. The engineering study must certify that the right of way savings and material savings exceed the cost of additional drainage structures required to mitigate the reduced gutter capacity. 6.9.3. Raised Median Noses To prevent vehicles from breaking the curb in the nose of raised medians, a monolithic section of curb and median pavement should be constructed. See GDOT Construction Standards and Details, Construction Details of Median Crossovers (M-3). 6.9.4. Raised Channelizing Islands Raised channelizing islands help control and direct the movement of traffic by reducing excess pavement areas, and channelizing turning movements at intersections. In urban locations, a sloped curb is generally used in conjunction with striping to delineate the island. In rural locations where higher speeds are likely, islands are typically delineated with a sloped curb and offset appropriately. In areas with crosswalks where raised islands will be used for pedestrian refuge, the geometry of the intersection and the right turn lanes may need to be modified to ensure that the raised islands are large enough to accommodate ramps and pedestrian refuge areas, along with support for pedestrian signals and control buttons, that are compliant with the Americans with Disabilities Act1 (ADA) guidelines. Raised islands should be offset from the travel lane as shown in the current GDOT Regulations for Driveway and Encroachment Control. Refer to Chapter 9 of the current AASHTO Green Book for additional information. Raised islands should be offset 4-ft from travel lanes when posted speeds are < 45 mph and 10-ft from travel lanes when posted speeds are > 45 mph. 6.10. Sidewalks See Section 9.5.1 Pedestrian Facility Design for design criteria related to sidewalks. 6.11. Barriers Chapters 5 and 6 of the AASHTO Roadside Design Guide provide details on the application and design of various barriers, including guardrail, cable, and concrete median barriers. Recommendations on the layout and type of barrier to be used are usually obtained from the Office of Bridge and Structural Design when bridges are involved. All other applications are the responsibility of the designer. 1 Visit the following FHWA web page for additional information relating to Americans with Disabilities Act (ADA) requirements http://www.fhwa.dot.gov/environment/te/te_ada.htm GDOT Design Policy Manual Revised 07/22/2011 6-9 6.11.1. Barrier Types The following barrier types should be used under the various stated conditions: Cable Barrier This is a flexible barrier capable of deflecting 12-ft or more when impacted. Barrier is typically used in the grassed medians of interstates and freeways. The designer shall account for the deflection when determining the location of the barrier. W-Beam Guardrail A semi-flexible barrier that will deflect up to 5-ft W-beam may be used to prevent vehicles from crossing medians, traversing steep slopes or striking objects. Cannot be used 8-ft from curb face. Refer to the GDOT Construction Standards and Details for additional guidance for placement of guardrail behind curbs. T-Beam Guardrail Similar to W-beam guardrail, but deflects only 3-ft T-beam is used on transitions from W-Beam to a Concrete Barrier. Refer to the GDOT Construction Standards and Details for additional guidance for placement of guardrail behind curbs. Double Faced Guardrail Semi-flexible barrier capable of deflecting 5-ft Used in medians and other locations to prevent errant vehicles from crossing into opposing traffic. Single Slope Concrete Barrier A rigid barrier with little or no deflection. Used for medians or side barrier directly in front of rigid objects that are near the traveled way. This includes walls and bridge bents. This is the preferred barrier for Interstates and new construction where Jersey shape barrier is not being retained. Jersey Shaped Concrete Barrier Same uses as single slope concrete barriers. May be used on projects where portions of existing Jersey barrier can be retained to provide a consistent design and appearance. Jersey barrier cannot be retained when construction raises the pavement surface by 3-inches or higher than the bottom lip of the barrier. Temporary Barriers The design, installation and maintenance of temporary barriers is discussed in the following documents: AASHTO Roadside Design Guide, Chapter 9 FHWA Manual on Uniform Traffic Control Devices (MUTCD)2, part 6 DOT Specifications, Section 150 GDOT Construction Standards and Details, Details of Precast Temporary Barrier (Ga. Std. 4961). Two methods of temporary barrier are used: Method 1 - Must be certified compliant with National Cooperative Highway Research Program (NCHRP) Report 3503 "Test Level 3" approved or meets the requirements of Ga. Std. 4961. Method 1 barrier is not suitable on bridges where the distance from the centerline of the barrier to the free edge of the bridge deck is less than or equal to 6-ft, measured normal to the barrier. 2 FHWA. Manual on Uniform Traffic Control Devices (MUTCD). 2003 The 2003 version of the MUTCD is available online at: http://mutcd.fhwa.dot.gov/kno-2003r1.htm 3 TRB. National Cooperative Highway Research Program (NCHRP) Report 350, Procedures for the Safety Performance Evaluation of Highway Features. 1992 Available online at: http://safety.fhwa.dot.gov/roadway_dept/road_hardware/nchrp_350.htm GDOT Design Policy Manual Revised 07/22/2011 6-10 Method 2 - Must be certified compliant with National Cooperative Highway Research Program (NCHRP) Procedures for the Safety Performance Evaluation of Highway Features (Report 350) "Test Level 3" and does not deflect more than 1-ft under NCHRP test conditions. A Method 2 barrier shall be used on bridges and bridge approaches where the distance from the centerline of the barrier to the free edge of the bridge deck is less than or equal to 6-ft measured normal to the barrier. Refer to the current AASHTO Roadside Design Guide for further discussion on the properties and uses of these barriers. 6.11.2. Glare Screens Glare screens are required on all interstate concrete median barriers. Glare screens for concrete barriers are typically constructed as concrete extensions but alternate materials may be used on a case-by-case basis. A glare screen is required between the mainline and frontage roads with opposing traffic flows. Where concrete barriers are not used, a glare screen such as landscaping materials, fencing with inserts or walls may be used to minimize glare. With offsets greater than 40-ft, glare screens are not required, but should be evaluated to determine if needed. 6.11.3. End Treatments All blunt approach ends of barriers should be protected in one of the following methods: Guardrail transition with a Type 12 anchorage the Type 12 is a gating or non-gating guardrail terminal. This end treatment requires a wider shoulder than the guardrail it is attaching to, so the designer must ensure that additional shoulder width is included for the Type 12 treatment. Energy absorption end treatment - attenuators must be installed in accordance to the manufacturer's recommendations. In general, attenuators should not be placed on a raised median. The median must be tapered so a stray vehicle impacts the barrier without being vaulted by the curb. Flared beyond the clear zone see GDOT Construction Standards and Details for flare rates. Temporary end treatments should be used in work zones, where warranted. Blunt ends are acceptable in urban areas where the blunt end is equal to or beyond the lateral offset specified in Chapter 5 of this Manual. For this condition, the end shall be tapered with a 6:1 slope. For additional information, refer to the current AASHTO Roadside Design Guide, Chapter 8; and all applicable GDOT Construction Standards and Details . 6.12. Medians GDOT has adopted the following "median usage" criteria as standard, having substantial importance to the operational and safety performance of a roadway such that special attention should be given to the design decision. The designer is encouraged to select a median dimension that provides a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. A decision to use a median dimension value that does not meet the standard criteria defined by GDOT shall require a comprehensive study by an engineer and the prior approval of a Design Variance from the GDOT Chief Engineer. GDOT Design Policy Manual Revised 07/22/2011 6-11 The following factors should be considered when determining the applicable median dimension along a roadway: functional classification; type of development; access management plan; number of lanes; base year traffic; design year traffic; posted speed limit; design speed; and accident/crash data. 6.12.1. Interstate Medians Interstates are required to have a depressed median or positive barrier separation in areas of rightof-way restrictions, as specified in the AASHTO Green Book. Positive barrier separation is required for all median widths 52-ft or where mutually exclusive clear zone for each direction of traffic cannot be obtained. Positive barrier separation is not required for median widths > 64-ft Median barrier is optional for median widths between 52-ft and 64-ft Positive barrier separation should be considered for all existing medians where there is a history of cross median type accidents. 6.12.2. Arterial Medians Multi-lane roadways with design speeds > 45 mph shall require the positive separation of opposing traffic using a median. Multi-lane roadways with three or more lanes in each direction shall include positive separation of opposing traffic using a median. A 24-ft raised median will require a sloped curb (Type 7 curb-face) inside the median, and a 2-ft additional paved shoulder offset from the edge of the inside travel-lane to the edge of the gutter (for a total of 4-ft inside shoulder width from the edge of travel-lane to the face of the curb). Raised medians shall be constructed on multi-lane roadways at intersections that exhibit one of the following characteristics: high turning volumes relating to 18,000 ADT (base year) and 24,000 ADT (design year); accident rate greater than the state average for its classification; and excessive queue lengths (as determined by District Traffic Engineer) in conjunction with excessive number of driveways. Median options for arterial roadways (including GRIP Corridors) are described in Table 6.3. Table 6.3. Median Options for Arterials (Including GRIP Corridors) Median Width ADT (Base Year) ADT (Design Year) Design Speeds 45 mph 5-lane section (14-ft flush median) 5-lane section (14-ft flush median)(1) 20-ft or 24-ft raised median(2) < 18,000 < 18,000 > 18,000 < 24,000 > 24,000 > 24,000 Design Speeds 55 mph GDOT Design Policy Manual Revised 07/22/2011 6-12 24-ft raised median 32-ft depressed median 44-ft depressed median n/a n/a n/a n/a n/a n/a Design Speeds 65 mph 44-ft depressed median n/a n/a (1) The project footprint should be designed and right-of-way purchased, to incorporate a future 20-ft raised median or preferably a 24-ft raised median where practical. The need to retrofit a flush median to a raised median section should be determined by the monitoring of accidents and traffic volumes on a five-year cycle by the Safety Engineer in the GDOT Office of Traffic Operations. (2) GDOT prefers the use of a 24-ft raised median where practical. 6.12.3. Medians at Pedestrian Crossings Locations where a significant number of pedestrians are likely to be crossing the roadway at midblock may warrant positive separation of opposing traffic using a median for pedestrian refuge. Signals are not typically warranted at these locations. Two-phase pedestrian crossings may be required when the roadway width requires excessive pedestrian crossing time (i.e. 6-lane section with dual left turn lanes and a right turn lane, etc). In the case of a two-phase pedestrian crossing, the median shall be wide enough to provide an ADA-compliant pedestrian refuge area. 6.13. Parking Lanes Generally, parking on arterial highways is prohibited because on-street parking decreases through capacity, impedes traffic flow, and increases accident potential. At the request of the local governing authority, consideration may be given to the inclusion of parking adjacent to the roadway in special situations if the following conditions are met: parking currently exists adjacent to the roadway; adequate off-street parking facilities are unavailable or unfeasible; the subsequent reduction in highway capacity will be insignificant; and the local governing authority has agreed to pay for the additional costs associated with the onstreet parking, such as additional right-of-way, construction costs, etc. When on-street parking is allowed on a roadway, parallel parking is the preferred type. Under certain circumstances, angled parking is allowed. However, angled parking presents sight distance problems due to the varying length of vehicles, such as vans and recreational vehicles. The extra length of these vehicles may also interfere with the traveled way. The type of on-street parking selected should depend on the specific function and width of the street, adjacent land uses and traffic volume. 6.14. Summary of Design Criteria for Cross Section Elements GDOT has developed the following tables to summarize the criteria used to design typical cross section elements for roadway classifications in Georgia with Average Daily Traffic greater than 2000 vehicles per day. The criteria listed within the tables represents typical geometric dimensions used to design common rural and urban type roadways according to the selected design speed. The tables are for reference only and do not reflect every possible design option available to the designer. Drawings of commonly used typical sections are also provided to illustrate the application of the criteria listed in the tables. The designer is encouraged to select design criteria that provides GDOT Design Policy Manual Revised 07/22/2011 6-13 a balance among the design vehicle, other users of the facility, and within the context of the surrounding environment. Table 6.4. Design Criteria for Local Roadways Table 6.5. Design Criteria for Collector Roadways Table 6.6. Design Criteria for Arterial Roadways Table 6.7. Design Criteria for Freeways GDOT Design Policy Manual Revised 07/22/2011 6-14 Table 6.4. Design Criteria for Local Roadways Cross Section Element Rural (open ditch sections) (ADT > 2000)(1) Urban (curbed sections) (ADT > 2000)(1) 2-Lane 2-Lane Design Speed Desirable Level of Service (LOS)(2) 35 mph C or D 45 mph C or D 55 mph C or D 25 mph C or D 35 mph C or D Traveled Way Lane width (min-desirable)(3) Cross Slope (normal) Superelevation (max) 11-12-ft 2% 6% 11-12-ft 2% 6% 11-12-ft 2% 6% 10-12-ft 2% 4% 10-12-ft 2% 4% Shoulders Overall width Paved width Cross Slope (normal) 8-ft 8-ft 10-ft n/a n/a 2-ft 2-ft 2-ft n/a n/a 6% 6% 6% n/a n/a Border Area (urban shoulder) (width) Cross Slope (normal) n/a n/a n/a 10-16-ft 10-16-ft n/a n/a n/a 2% 2% Sidewalk (SW) Width of Sidewalk Desirable buffer from back of curb to SW Cross Slope (max) Width of Bike Lanes Foreslope (max/normal)(6) Width of foreslope in cut n/a n/a n/a 4-ft(4) 2:1/4:1 10-ft n/a n/a n/a 4-ft(4) 2:1/4:1 12-ft n/a n/a n/a 4-ft(4) 2:1/4:1 12-ft 5-ft 6-ft 2% 4-ft(5) 2:1/4:1 n/a 5-ft 6-ft 2% 4-ft(5) 2:1/4:1 n/a Ditch Bottom (width) Backslope (max/normal)(6) Vertical Clearance (min-desirable)(7)(ft) Lateral Offset to Obstruction(8) Clear Zone(9) 2-ft 2:1/4:1 14.5-16.75 Ch. 5 18-ft 4-ft 2:1/4:1 14.5-16.75 Ch. 5 24-ft 4-ft 2:1/4:1 14.5-16.75 Ch. 5 26-ft n/a 2:1/4:1 14.5-16.75 Ch. 5 AASHTO n/a 2:1/4:1 14.5-16.75 Ch. 5 AASHTO Notes: (1) Values shown are for roadways with ADT > 2000. Refer to the current AASHTO Green Book for design criteria on roadways with ADT < 2000, and the AASHTO "Guidelines for Geometric Design of Very Low-Volume Local Roads" for design criteria on roadways with ADT 400. (2) LOS D is appropriate in heavily developed urban or suburban areas. (3) See AASHTO Green Book, Chapter 5, Local Roads and Streets, for conditions to construct or retain 10 and 11-ft lanes. (4) Bike Lane is incorporated into the overall width of a 6.5-ft paved shoulder to include a 16-inch rumble strip and total 12-inch buffer area (refer to Ga. Construction Detail S-8). See Section 9.4.2 Bicycle Warrants. (5) Bike Lane measured from the outside edge of traveled-way outward. Does not include curb & gutter or header curb. (6) The use of a slope inside the "Clear Zone" that is steeper than 4:1 will require the installation of a roadside barrier (i.e. guardrail, barrier wall, crash attenuator, etc...) (See Ga.Std.Details, 4000 series). (7) 14.5-ft is permissible, provided a suitable bypass exists for tall vehicles. For additional guidelines, refer to Chapter 2.3.2 of the GDOT Bridge and Structures Policy Manual. http://www.dot.ga.gov/doingbusiness/PoliciesManuals/roads/BridgeandStructure/GDOT_Bridge_and_Structures_Policy_Manual.pdf (8) For rural roadways, lateral offset is measured from the edge of traveled way outward. For urban roadways with curbed sections, lateral offset is measured from the face of curb outward. See Chapter 5 of this Manual for GDOT guidelines on lateral offset to signs, light poles, utility installations, signal poles and hardware, and trees and shrubs. (9) AASHTO defines Clear Zone as the unobstructed relatively flat area beyond the edge of traveled way for the recovery of errant vehicles. Clear zone recommendations are a function of design speed, traffic volumes, and embankment slope. For Clear Zone recommendations, refer to the current edition of the AASHTO Roadside Design Guide, Ch 3. GDOT Design Policy Manual Revised 07/22/2011 6-15 Table 6.5. Design Criteria for Collector Roadways Cross Section Element Rural (open ditch sections) (ADT > 2000)(1) Urban (curbed sections) (ADT > 2000)(1) 2-Lane 4-Lane 2-Lane 4-Lane Design Speed Desirable Level of Service (LOS) 45 mph C 55 mph C 25 mph C or D(2) 35 mph C or D(2) 45 mph C or D(2) Traveled Way Lane width (min-desirable)(3) Cross Slope (normal) 11-12-ft 2% 11-12-ft 2% 11-12-ft 2% 11-12-ft 2% 11-12-ft 2% Superelevation (max) 6% 6% 4% 4% 4% Shoulders (outside) Overall width Paved width Cross Slope (normal) 8-ft 10-ft n/a n/a n/a 4-ft/6.5-ft(4) 6.5-ft n/a n/a n/a 6% 6% n/a n/a n/a Shoulders (median) Overall width Paved width n/a 6-ft n/a n/a n/a n/a 2-ft n/a n/a n/a Cross Slope (normal) n/a 4% n/a 4% 4% Border Area (urban shoulder) (width) Cross Slope (normal) n/a n/a 10 -16-ft 10 -16-ft 10 -16-ft n/a n/a 2% 2% 2% Width of Median Depressed Raised n/a 32 - 44-ft n/a n/a 24-ft n/a n/a 20-ft n/a 20-ft Flush n/a n/a n/a 14-ft 14-ft Sidewalk (SW) Width of Sidewalk n/a n/a 5-ft 5-ft 5-ft Desirable buffer from back of curb to SW Cross Slope (max) Width of Bike Lanes Foreslope (max/normal)(6) n/a n/a 4-ft(4) 2:1/4:1 n/a n/a 4-ft(4) 2:1/4:1 6-ft 2% 4-ft(5) 2:1/4:1 6-ft 2% 4-ft(5) 2:1/4:1 6-ft 2% 4-ft(5) 2:1/4:1 Width of foreslope in cut 12-ft 12-ft n/a n/a n/a Ditch Bottom (width) Backslope (max/normal)(6) Vertical Clearance (min-desirable)(7)(ft) Lateral Offset to Obstruction(8) 2-ft 2:1/4:1 16.5 -16.75 Ch. 5 4-ft 2:1/4:1 16.5 -16.75 Ch. 5 n/a 2:1/4:1 16.5-16.75 Ch. 5 n/a 2:1/4:1 16.5 -16.75 Ch. 5 n/a 2:1/4:1 16.5 -16.75 Ch. 5 Clear Zone(9) 24-ft 26-ft AASHTO AASHTO AASHTO Notes: (1) Values shown are for roadways with ADT > 2000. Refer to the current AASHTO Green Book for design criteria on roadways with ADT < 2000, and the AASHTO "Guidelines for Geometric Design of Very Low-Volume Local Roads" for design criteria on roadways with ADT 400. (2) LOS D is appropriate in heavily developed urban and suburban areas. (3) See AASHTO Green Book, Chapter 6, Collector Roads and Streets, for conditions to construct or retain 11-ft lanes. (4) Bike Lane is incorporated into the overall width of a 6.5-ft paved shoulder to include a 16-inch rumble strip and total 12-inch buffer area (refer to Ga. Construction Detail S-8). See Section 9.4.2 Bicycle Warrants. (5) Bike Lane measured from the outside edge of traveled-way outward. Does not include curb & gutter or header curb. (6) The use of a slope inside the "Clear Zone" that is steeper than 4:1 will require the installation of a roadside barrier (i.e. guardrail, barrier wall, crash attenuator, etc...) (See Ga.Std.Details, 4000 series). (7) For additional guidelines, refer to Chapter 2.3.2 of the GDOT Bridge and Structures Policy Manual. (8) For rural roadways, lateral offset is measured from the edge of traveled way outward. For urban roadways with curbed sections, lateral offset is measured from the face of curb outward. See Chapter 5 of this Manual for GDOT standard criteria for lateral offset to signs, light poles, utility installations, signal poles and hardware, and trees and shrubs. (9) AASHTO defines Clear Zone as the unobstructed, relatively flat area beyond the edge of traveled way for the recovery of errant vehicles. Clear zone recommendations are a function of design speed, traffic volumes, and embankment slope. For Clear Zone recommendations, refer to the current edition of the AASHTO Roadside Design Guide, Ch 3. GDOT Design Policy Manual Revised 07/22/2011 6-16 Table 6.6. Design Criteria for Arterial Roadways Cross Section Element Rural (open ditch sections) (ADT > 2000)(1) Urban (curbed sections) (ADT > 2000)(1) 2-Lane 2-Lane 4-Lane 4-Lane 4-Lane 4-Lane Design Speed Desirable Level of Service (LOS) 45 mph B 55 mph B 55 mph B 65 mph B 45 mph C or D(2) 55 mph C or D(2) Traveled Way Lane width (min-desirable)(3) Cross Slope (normal) 11-12-ft 2% 11-12-ft 2% 11-12-ft 2% 11-12-ft 2% 11-12-ft 2% 11-12-ft 2% Superelevation (max) 6% 6% 6% 6% 4% 4% Shoulders (outside) Overall width Paved width Cross Slope (normal) 8-ft 10-ft 10-ft 10-ft n/a n/a 4-ft /6.5-ft(4) 4-ft /6.5-ft(4) 6.5-ft 6.5-ft n/a n/a 6% 6% 6% 6% n/a n/a Shoulders (median) Overall width (cross slope) n/a n/a 6-ft (4%) 6-ft (4%) n/a n/a Paved width (cross slope with mainline) n/a n/a 2-ft (2%) 2-ft (2%) n/a 2-ft Border Area (urban shoulder) (width) n/a n/a n/a n/a 10 -16-ft 10 -16-ft Cross Slope (max) n/a n/a n/a n/a 2% 2% Width of Median Depressed n/a n/a 32 - 44-ft 44-ft n/a n/a Raised Flush n/a n/a 24-ft n/a 20-ft 24-ft n/a n/a n/a n/a 14-ft n/a Sidewalk (SW) Width of Sidewalk n/a n/a n/a n/a 5-ft 5-ft Desirable buffer from back of curb to SW n/a n/a n/a n/a 6-ft 6-ft Cross Slope (max) Width of Bike Lanes Foreslope (max/normal)(6) Width of foreslope in cut n/a 4-ft(4) 2:1/4:1 12-ft n/a 4-ft(4) 2:1/4:1 12-ft n/a 4-ft(4) 2:1/4:1 12-ft n/a 4-ft(4) 2:1/6:1 18-ft 2% 4-ft(5) 2:1/4:1 n/a 2% 4-ft(5) 2:1/4:1 n/a Ditch Bottom (width) Backslope (max/normal)(6) Vertical Clearance (min-desirable)(7)(ft) Lateral Offset to Obstruction(8) 2-ft 2:1/4:1 16.5-16.75 Ch. 5 4-ft 2:1/4:1 16.5-16.75 Ch. 5 4-ft 2:1/4:1 16.5-16.75 Ch. 5 4-ft 2:1/6:1 16.5-16.75 Ch. 5 n/a 2:1/4:1 16.5-16.75 Ch. 5 n/a 2:1/4:1 16.5-16.75 Ch. 5 Clear Zone(9) 24-ft 26-ft 26-ft 32-ft AASHTO AASHTO Notes: (1) Values shown are for roadways with ADT > 2000. Refer to the current AASHTO Green Book for design criteria on roadways with ADT< 2000, and the AASHTO "Guidelines for Geometric Design of Very Low-Volume Local Roads" for design criteria on roadways with ADT 400. (2) LOS D is appropriate in heavily developed urban and suburban areas. (3) See AASHTO Green Book, Chapter 7, Rural and Urban Arterials, for conditions to construct or retain 11-ft lanes. (4) Bike Lane is incorporated into the overall width of a 6.5-ft paved shoulder to include a 16-inch rumble strip and total 12-inch buffer area (refer to Ga. Construction Detail S-8). See Section 9.4.2 Bicycle Warrants. (5) Bike Lane measured from the outside edge of traveled-way outward. Does not include curb & gutter or header curb. (6) The use of a slope inside the "Clear Zone" that is steeper than 4:1 will require the installation of a roadside barrier (i.e. guardrail, barrier wall, crash attenuator, etc...) (See Ga.Std.Details, 4000 series). (7) For additional guidelines, refer to Chapter 2.3.2 of the GDOT Bridge and Structures Policy Manual. (8) For rural roadways, lateral offset is measured from the edge of traveled way outward. For urban roadways with curbed sections, lateral offset is measured from the face of curb outward. See Chapter 5 of this Manual for GDOT standard criteria for lateral offset to signs, light poles, utility installations, signal poles and hardware, and trees and shrubs. (9) AASHTO defines Clear Zone as the unobstructed, relatively flat area beyond the edge of traveled way for the recovery of errant vehicles. Clear zone recommendations are a function of design speed, traffic volumes, and embankment slope. For Clear Zone recommendations, refer to the current edition of the AASHTO Roadside Design Guide, Ch 3. GDOT Design Policy Manual Revised 07/22/2011 6-17 Table 6.7. Design Criteria for Freeways Cross Section Element Rural (graded shoulders and ditches) (ADT > 6000) Urban (depressed/restricted R/W) (ADT > 6000) 4 6 Lane 4 6 Lane Design Speed Desirable Level of Service (LOS) 70 mph B or C(1) 55 mph C or D(2) 65 mph C or D(2) Traveled Way Lane width Cross Slope (normal) Superelevation (maximum) 12-ft 2% 8% 12-ft 2% 6% 12-ft 2% 6% Shoulders (outside) Overall width Paved width 14-ft 12-ft 14-ft 12-ft 14-ft 12-ft Shoulders (median) Overall width Paved width 12-ft 10-ft(3) 12-ft 10-ft(3) 12-ft 10-ft(3) Width of Median Depressed Continuous Barrier (6-lanes) Continuous Barrier (8-lanes) Foreslope (max/normal)(4) Width of foreslope in cut 52-64-ft n/a n/a 2:1/6:1 18-ft n/a 30 40-ft 28 30-ft 2:1/6:1 n/a n/a 30 40-ft 28 30-ft 2:1/6:1 n/a Ditch Bottom (width) Backslope (max/normal)(4) Vertical Clearance (min-desirable)(5)(ft) Lateral Offset to Obstruction(8) Clear Zone(7) 4-ft 2:1/4:1 16.5-17 Ch. 5 36-ft n/a 2:1/4:1 16.5-17 Ch. 5 AASHTO n/a 2:1/4:1 16.5-17 Ch. 5 AASHTO Note: (1) LOS C is appropriate for developing rural and suburban areas and for auxiliary lanes. (2) LOS D is appropriate in heavily developed urban areas. (3) A 12-ft wide paved inside shoulder should be used on Freeways with six or more lanes, and truck volumes greater than 250 vehicles/hour. (4) The use of a slope inside the "Clear Zone" that is steeper than 4:1 will require the installation of a roadside barrier (i.e. guardrail, barrier wall, crash attenuator, etc...) (See Ga.Std.Details, 4000 series). (5) For additional guidelines, refer to Chapter 2.3.2 of the GDOT Bridge and Structures Policy Manual. (6) For Freeways, lateral offset is measured from the edge of traveled way outward. See Chapter 5 of this Manual for GDOT standard criteria for lateral offset to signs, light poles, utility installations, signal poles and hardware, and trees and shrubs. (7) AASHTO defines Clear Zone as the unobstructed, relatively flat area beyond the edge of traveled way for the recovery of errant vehicles. Clear zone recommendations are a function of design speed, traffic volumes, and embankment slope. For Clear Zone recommendations, refer to the current edition of the AASHTO Roadside Design Guide, Ch 3. GDOT Design Policy Manual Revised 07/22/2011 6-18 Figure 6.2. Illustration of Typical Dimensions for Urban Local Roadways GDOT Design Policy Manual Revised 07/22/2011 6-19 Figure 6.3. Illustration of Typical Dimensions for Rural Local Roadways GDOT Design Policy Manual Revised 07/22/2011 6-20 Figure 6.4 Illustration of Typical Dimensions for Collector and Arterial Roadways Figure 6.5. Illustration of Typical Dimensions for Urban Freeway Figure 6.6. Illustration of Typical Dimensions for Interchange Ramps GDOT Design Policy Manual Revised 07/22/2011 6-23 Chapter 6 Index Barriers End Treatments, 11 Glare Screens, 11 Guardrail, 10, 11 Jersey, 10 Temporary, 10 Types, 10 Cross Section Barriers. See Barriers Curbs. See Curbs Elements, 314 Medians, 1214 Parking Lanes, 14 Typical Section Geometrics, 3 Cross-over Crown Break. See Pavement, Crown Curbs, 49 Glare Screens. See Barriers, Glare Screens Guardrail. See Barriers, Guardrail Jersey Barrier. See Barriers, Jersey Medians Cross Section, 1214 Interstate, 12 Pedestrian Crossings, 13 One-way Tangent Crown. See Pavement, Crown Parking Lanes. See Cross Section, Parking Lanes Pavement Crown, 3 Type Determination, 3 Pedestrian Facilities Medians. See Medians, Pedestrian Crossings Temporary Barriers. See Barriers, Temporary Two-way Tangent Crown. See Pavement, Crown GDOT Design Policy Manual Revised 07/22/2011 6-24 Chapter 7 Contents 7. AT GRADE INTERSECTIONS 2 7.1. Intersection Design Elements 2 7.2. Intersection Geometrics 2 7.2.1. Angle of Intersection/Skew Angle 2 7.2.2. Right-of-Way Flares 2 7.2.3. Turn Lanes 3 7.2.4. Islands 3 7.2.5. Intersection Radii 3 7.3. Median Openings 4 7.4. Driveways 5 7.5. Signalization 5 7.5.1. New Intersections and Existing Unsignalized intersections 7 7.5.2. Signal Modification 7 7.5.3. Geometric Design Elements 8 7.6. Highway-Railroad Grade Crossings 8 7.6.1. Horizontal Alignment 9 7.6.2. Vertical Alignment 9 7.6.3. Highway-Rail Grade Traffic Control Considerations 10 7.6.4. Traffic Control Devices 11 7.6.5. Alternatives to Maintaining the Crossing 12 7.6.6. Crossing Consolidation and New Crossings 13 7.6.7. GDOT At-Grade Highway-Rail Crossing Evaluation Criteria 14 Chapter 7 Index 16 Summary of Chapter 7 Revisions 17 GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-1 7. AT GRADE INTERSECTIONS The American Association of State Highway and Transportation Officials (AASHTO) A Policy on the Geometric Design of Highways and Streets (Green Book) defines an intersection as, "the general area where two or more highways join or cross, including the roadway and roadside facilities for traffic movements within the area". The main objective of intersection design should be to facilitate the safe and efficient movement of motor vehicles, buses, trucks, bicycles, and pedestrians. 7.1. Intersection Design Elements The mobility and operational characteristics of a facility will depend on proper intersection design. Intersection design should closely fit the natural paths and operating characteristics of its users. The five basic elements that should be considered in intersection design are: Human Factors - driving habits, the ability of motorists to make decisions, driver expectations, decision and reaction time, conformance to natural paths of movement, pedestrian use and habits, bicycle use and habits. Traffic Considerations - design and actual capacities, design-hour turning movements, size and operating characteristics of vehicle, variety of movements (diverging, merging, weaving, and crossing), vehicle speeds, transit involvement, crash experience, bicycle movements, pedestrian movements. Physical Elements - character and use of abutting property, horizontal and vertical alignments at the intersection, sight distance, angle of the intersection, conflict area, speed-change lanes, geometric-design features, traffic control devices, lighting equipment, safety features, bicycle traffic, environmental factors, cross walks, parking, directional signing and marking. Economic Factors - cost of improvements, effects of controlling or limiting rights-of-way on abutting residential or commercial properties where channelization restricts or prohibits vehicular movements, energy consumption. Functional Intersection Area - boundary (much larger than the physical intersection; includes perception-reaction distance, maneuver distance, deceleration distance and queue-storage distance), access points. 7.2. Intersection Geometrics 7.2.1. Angle of Intersection/Skew Angle Refer to Chapter 4, Elements of Design, Section 4.1.5. Intersection Sight Distance, of this manual for design policies concerning angle of intersection/skew angle. 7.2.2. Right-of-Way Flares Refer to Chapter 4, Elements of Design, Section 4.1.5. Intersection Sight Distance, for design policies concerning right-of-way flares. GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-2 7.2.3. Turn Lanes The length of a turn lane consists of three components: entering taper, deceleration length, and storage length. Where practical, the total length of turn lane should be determined based on the design speed and the storage requirement for the turn lane and adjacent through-lane queue. At a minimum, for design speeds < 45 mph, taper and deceleration lengths should be designed in accordance with the GDOT Regulations for Driveway and Encroachment Control. At a minimum, for design speeds 45 mph, taper and deceleration lengths should be designed in accordance with Georgia Construction Detail M-3 For further design guidance relating to the design of turn lanes, refer to the AASHTO Green Book, Chapter 9, Auxiliary Lanes. The following guidelines have been adopted by GDOT for the placement of deceleration lanes on multi-lane roadways with median widths greater than 12-ft: Left-Turn-Lanes should be incorporated inside the median at all median opening locations. When the posted speed is 45 mph, Right-Turn-Lanes should be placed at paved public street intersections and entrances to major traffic generators. When the posted speed is < 45 mph, Right-Turn-Lanes should be placed at paved public street intersections and direct entrances to major traffic generators under the following conditions: a. Mainline current traffic volumes exceed 10,000 vehicles per day, and b. Traffic volumes on the side road exceed 200 vehicles per day with peak hour right turn movements from the main road exceeding 20 vehicles per hour. In addition, every effort should be made to replace existing right turn lanes at commercial driveways when practical. The benefits of including a turn lane may not always outweigh the impacts the turn lane will have on adjacent parcels. Sound engineering judgment should be used to determine if the benefits of replacing the right turn lane outweigh the impacts. Coordination with the Division of Engineering, Office of Traffic Operations, and District Access Management Engineer is recommended. 7.2.4. Islands AASHTO defines an island as, "the area between traffic lanes used for control of vehicle movement. Islands also provide for an area for pedestrian refuge and traffic control devices". Islands may be raised or painted. AASHTO defines a refuge island as, "A refuge island for pedestrians is one at or near a crosswalk or bicycle path that aids and protects pedestrians and/or bicyclists who cross the roadway". Refuge islands should be considered in areas where the roadway is too wide to allow a pedestrian to cross the entire intersection in one movement. 7.2.5. Intersection Radii Turning radii treatments for intersections are important design elements that affect the operation, safety, and construction costs of the intersection. Several basic parameters should be considered in determining the appropriate corner radii and length of median opening including: intersection angle, number and width of lanes, design vehicle turning path, clearances, encroachment into oncoming or opposing lanes, parking lanes, shoulders, and pedestrian needs. The GDOT Driveway Manual provides typical radii for various applications. GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-3 7.3. Median Openings Median openings should be planned and designed to reflect access management objectives along a roadway. The following guidelines should be considered when designing median openings as well as when requests are received for additional median openings on completed roadway sections: Priority should be given to establishing median openings at existing roads and streets before other locations. The location and design of a median opening should take into consideration the taper length, deceleration length, and storage length required to adequately satisfy the traffic volumes, and whether adequate space is available between adjacent median openings to satisfy these critical dimensions. Adequate sight distance should be available at all median opening locations. GDOT has adopted 1,000-ft. as the preferred minimum spacing between median openings in urban areas, and 1320-ft. as the preferred minimum spacing between median openings in rural areas. In urban areas, median openings may be spaced less than 1,000-ft., and greater than 660-ft. if it can be demonstrated that left turning volumes are nominal. The maximum spacing between median openings in developed areas (including single occupied residence) should be one mile. In areas without any development or where there are no driveways due to access control, the maximum spacing between median openings should be 2 miles. In urban areas a practical maximum spacing between median openings is approximately mile. Since it is preferable to place median openings only at local roads, the opening may be shifted slightly to line up with an existing road or major traffic generator. Median openings for new and reconstructed facilities should be constructed in accordance with GDOT Construction Standards and Details, M-3, Type A, B, or C. The Type B design is preferred and should be used where drainage can be adequately designed and speeds are greater than or equal to 55 mph. Consideration for use of Type B crossovers should also be given when engineering judgment dictates that the design is practical in median widths less than 32-ft. and when there are more than two approach through lanes. Additional pavement for U-turns at median openings should be considered where there is a demand for access and where practical. In some cases, pavement for truck U-turns such as jug handles may be necessary to satisfy access to private property between successive median openings. Refer to the GDOT Construction Standards and Details, Construction Detail M-3, Type C Median Crossover. The designer should also refer to the National Cooperative Highway Research Program (NCHRP) report, Safety of U-Turns at Unsignalized Median Openings (Report 524), when designing intersections with U-turn capability. For six-lane roadways, full median openings should be granted only at signalized intersections. Median openings should not typically be installed or permitted to serve a particular development; however, when it can be demonstrated that such an installation will benefit the overall safety, traffic flow and efficiency of the roadway, then consideration will be given. Consideration for installing median openings for particular developments also involves the application of standard access control policy; therefore, if a particular development is proposing to add a median opening to a roadway, and the design does not comply with design criteria adopted by GDOT, then the approval of a Design Variance from the GDOT Chief Engineer will be required prior to incorporating the opening or feature into a project design or along an existing roadway section. GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-4 7.4. Driveways GDOT considers driveways, or non-roadway access points to the State Route System, as essentially low-volume intersections that merit special consideration in their design and location. The designer should be familiar with the policies and procedures described in the current version of GDOTs Regulations for Driveway and Encroachment Control (Driveway Manual). New driveways and modifications to existing driveways are regulated through the use of permits. Driveway permits (referred to as "access permits") are necessary in order to preserve the functional integrity of the State Highway System and to promote the safe and efficient movement of people and goods. Access permit regulations generally control right-of-way encroachment and driveway design, location, and number. Access approved for newly constructed commercial developments may, and in-fact often, stipulate parking requirements (for parking adjacent to state-owned rights of way) and setback distances to buildings and/or sign structures. When a roadway is widened, parking, setback distances, ingress/egress and parcel circulation may be impacted. A consistent design approach should be applied to both existing driveways requiring reconstruction and proposed driveways for new developments. All reconstructed driveways should be compliant with the GDOT Driveway Manual. However, given the constraints of reconstructing an existing driveway, GDOT recognizes that it may not always be possible to reconstruct a driveway in strict accordance with the GDOT Driveway Manual. When roadways are to be widened, the replacement driveway may not require the same access/egress features, such as a right turn deceleration lane and/or acceleration lane. The need for the replacement of these features shall be evaluated on a case by case basis. In some cases replacement of access features in kind may not be justified due to excessive impacts to adjacent parcels. The safety and efficiency of the State Highway System are affected by the amount and character of intersecting streets and driveways. While it is recognized that property owners have certain right of access, the public also has the right to travel on the road system with relative safety and freedom from interference. It is GDOTs intent to balance the often conflicting interests of property owners and the traveling public. 7.5. Signalization The designer should be familiar with the current version of the GDOT TOPPS 6785-11, Traffic Signals. The information contained in this Section is intended to supplement the information contained in TOPPS 6785-1. The following provides some general guidelines for signalized intersection design: All signalized intersections shall be designed in accordance with the GDOT Traffic Signal Design Guidelines. Distance between stop bars on opposing movements should be set to minimum standards wherever possible, thus minimizing necessary clearance timings. 1 TOPPS 6785-1 is available on the GDOT Transportation Online Policies and Procedures System (TOPPS) at: http://www.dot.ga.gov/doingbusiness/PoliciesManuals/Pages/topps.aspx GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-5 The use of pedestrian refuge islands should be considered whenever possible to minimize pedestrian clearance times. The designer should communicate with the District Utilities Engineer to compile a list of all utilities which may be affected both underground and overhead. The location of utilities should be included on the signal plans so that they may be avoided. Special attention should be given to overhead utilities crossing the intersection to ensure that they do not conflict with the proposed signal span wire, mast arms, or signal heads, and that the design is able to meet National Electric Safety Code requirements. Actual (existing) and projected (design) volumes, including turn movements, should be collected and determined for the intersection. The designer should determine if the proposed signal will be part of a coordinated signal system, and if so, the development of communication plans or timing plans are needed. The designer should closely evaluate the sequence of construction and maintenance of traffic to determine if temporary signals are needed. Where possible signal poles / mast arms should be located to allow for use with both temporary signalization, and final signalization. The intersection controller cabinet shall be located where it can be utilized in the temporary signals, as well as the final signal design. Location of the PED button and PED signal, curb cut ramps, strain pole, controller cabinets, crosswalk and landing areas, should all be coordinated to ensure a fully accessible intersection. The designer should check the right of way to ensure that there is enough room to install these items. The intersection controller cabinet shall be located to avoid creating a sight distance obstruction in all phases of construction. Signal heads shall be designed with sufficient slack wiring to allow the heads to be relocated to different places on the span wire / mast arm for use in both the temporary and final signals. Wherever possible, loops, pull boxes, and loop lead-ins shall be placed to be used for both the temporary signals as well as the final signals. For signals mounted on mast arms, the designer should provide sufficient length on the arms to allow for both future signal heads, as well as field adjustments if needed. The designer should contact the maintaining agency that is responsible for the existing intersections in the area to determine design standards which may be unique to the area. As applicable, the construction of the signalized intersection should be carefully considered when developing maintenance of traffic plans. Consider decision sight distance as it relates to signal head and traffic control devices, and the queue length for the signal. GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-6 When designing a roadway or roadway improvements, particular attention should be paid to the future operations at the project intersections. Where existing signalization does not exist, the intersection should be evaluated to determine if signalization is required as part of the project. If the project includes an existing signalized intersection, the intersection should be evaluated to determine if improvements are required as part of the project. 7.5.1. New Intersections and Existing Unsignalized intersections At existing non-signalized and new intersections which are a part of the project design, the designer should request the District Traffic Operations Engineer perform a Traffic Engineering Study (including a signal warrant analysis) to determine if signalization may be warranted. The results of the study, along with the recommendations shall be documented in a Traffic Engineering Report. The signal warrant analysis shall be performed in accordance with the current version of the FHWA Manual on Uniform Traffic Control Devices (MUTCD)2. The Traffic Engineering Study should be performed under two separate scenarios: At locations where the intersections exist in the field, the intersection should be evaluated under existing volumes (as determined by field counts) and future lane configuration (based on the project design). If the intersection meets warrants under these conditions, the signal design should be included in the design package, and the signal should be installed as part of the project construction. At locations where an intersection exists in the field but does not meet warrants under existing traffic conditions, and at locations where the intersection does not exist in the field (new intersection as part of the design project) the intersection should be evaluated using design volumes (volumes developed as part of a traffic study) and future lane configuration (based on project design). Intersections that meet warrants under this scenario should be considered for inclusion in the design package. The designer should work closely with the District Traffic Operations Engineer to determine if signalization should occur as part of the project, or in a future stage. In either case, the roadway / intersection should be designed to allow for future signalization. Necessary turn lanes should be provided, or space to develop future turn lanes should be planned. Right-of-way should be provided for future signal poles and intersection equipment. 7.5.2. Signal Modification New signal plans should be developed for all existing signalized intersections where roadway improvements are being made. The existing signalized intersection should be evaluated to determine its existing operation. The intersection should then be analyzed with both existing volumes and design volumes using the future lane configuration to determine the appropriate intersection phasing. If future phasing changes will be needed, design allowance should be incorporated to provide room for additional signal heads, loop detectors, and mast arm lengths. Any modification to existing signals requires a revision to the existing signal permit. 2 FHWA. Manual on Uniform Traffic Control Devices (MUTCD). The 2003 version is available online at: Available online at: http://mutcd.fhwa.dot.gov/kno-2003r1.htm GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-7 7.5.3. Geometric Design Elements In rural areas, if there will be an auxiliary lane for acceleration after a right turn movement, it must provide adequate acceleration length to merge into traffic (as discussed in this Manual in Chapter 4, Elements of Design, Section 4.2.5. Transition in Number of Lanes). The lane must also be free of any driveways for the length of the auxiliary lane. 7.6. Highway-Railroad Grade Crossings When a Highway- Railroad grade crossing is included on a project, designers should coordinate with the GDOT Railroad Crossing Manager, Railroad Crossing Improvement Unit3, in conjunction with concept development for a transportation improvement project. The designer should be familiar with most current versions of the following resources: AASHTO A Policy on the Geometric Design of Highways and Streets (Green Book), Chapter 9. Intersections American Railway Engineering and Maintenance of Way Association (AREMA) specifications (visit www.arema.org for additional information) Railway company regulations GDOT Standard Drawing and Specifications FHWA Manual on Uniform Traffic Control Devices (MUTCD) A highway-railroad crossing involves either a separation of grades or a crossing at-grade. GDOT strongly encourages consideration of grade separated highway-railroad crossings. However, topographical and/or right-of-way limitations may make at-grade crossings the more feasible option. When an at-grade, highway-railroad crossing is included in the design of a roadway construction/reconstruction project, train-activated warning devices (i.e. gates, lights, and bells) shall be included in the design. Train-activated warning devices provide drivers with a positive indication of the presence or the approach of a train at the crossing. The geometric design of a highway-railroad grade crossing involves the elements of alignment, profile, sight distance, and cross section. The roadway should cross the railroad at- or nearly at- a right angle. The roadway gradient should be flat at- and adjacent to- the railroad crossing to permit vehicles to stop, when necessary, and then proceed across the tracks without difficulty. The vehicle operator can observe an approaching train and bring the vehicle to a stop prior to encroaching into the crossing area. Also the roadway width at all crossings should be the same as the roadway width approaching the crossing. 7 The Railroad Crossing Improvement Office (see http://www.dot.state.ga.us/dot/operations/traffic-safetydesign/subunit/rrcross.shtml) is a unit of the GDOT Office of Traffic Safety and Design (home page: http://www.dot.state.ga.us/dot/operations/traffic-safety-design/index.shtml). GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-8 7.6.1. Horizontal Alignment As per the AASHTO Green Book (2004), to the extent practical: The highway should be designed to intersect the railroad tracks at a right angle. There should be no intersections or driveways, and in areas where a highway intersection is close to a railroad crossing, sufficient distance between the tracks and the highway intersections should be provided to enable highway traffic in all directions to move expeditiously. Where adequate storage distance between the main track and a highway intersection is not available, interconnection of the highway traffic signals with the trainactivated warning devices and appropriate signage and pavement markings is strongly recommended. Placement of crossings on highway or railroad curves should be avoided because a roadway curvature can inhibit a drivers view of the crossing ahead, a railroad curvature may inhibit a drivers view down the tracks from both a stopped position at the crossing and on the approach to the crossing, and crossings located on both highway and railroad curves present maintenance problems and poor rideability for highway traffic due to conflicting superelevations. 7.6.2. Vertical Alignment As per the AASHTO Green Book (2004), to the extent practical: Highway and railroad intersections should be level: The crossing surface should be at the same plane as the top of the rails for a distance of 2ft. outside the rails. This is done to prevent low clearance vehicles from becoming caught on the railroad tracks. The surface of the highway should not be more than three inches higher or lower than the top of the nearest rail at a point 30-ft. from the rail, unless track superelevation makes a different level appropriate. If a roadway approach section is not level, or if the rails are superelevated, adequate rail clearances should be determined through a site-specific analysis. Vertical curves should be of sufficient length to ensure an adequate view of the crossing. Vertical curves should be used to traverse from the highway grade to a level plane at the elevation of the rails. GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-9 7.6.3. Highway-Rail Grade Traffic Control Considerations Highway-rail grade crossing traffic control considerations are discussed in detail in the FHWA publication, Guidance on Traffic Control Devices at Highway-Rail Grade Crossings4. The following discussion summarizes the key points of this FHWA publication. At a highway-rail grade crossing, the train always has the right of way. The process for determining the types of highway traffic control device(s) that are needed at a highway-rail grade crossing, or if a highway-rail crossing should exist, involves two-steps: Required Information - identifying what information the vehicle driver needs to be able to cross safely System operating characteristics - determining if the resulting driver response to a traffic control device is "compatible" with the intended system operating characteristics of the highway and the railroad facility. Required Information The first step involves three essential elements required for ,,safe passage through an at-grade crossing, which are incidentally the same elements a driver needs for crossing a highway-highway intersection: Advance notice / stopping sight distance this element involves the drivers ability to see a train and/or the traffic control device at the crossing ahead to bring the vehicle to a stop at least 15-ft. short of the near rail. Traffic control device comprehension this element is a function of the types of traffic control devices at the highway-rail crossing. According to FHWA, "there are typically three types of control devices, each requiring a distinct compliance response per the Uniform Vehicle Code, various Model Traffic Ordinances, and state regulations" (2002). These three types of control devices are: crossbuck, operating flashing lights that have the same function as a STOP sign, and flashing lights with lowered gates that have the same function as a red vehicular traffic signal. Driver decision to proceed through the grade crossing - this element concerns the drivers decision to safely proceed through the grade crossing. It involves sight distance available both on the approach and at the crossing itself. System Operating Characteristics The second step involves a traffic control device selection process considering respective highway and rail system operational requirements. Within these contexts, FHWA notes the following operation and safety variables that should be considered (2002): highway - AADT (Annual Average Daily Traffic), legal and/or operating speed 8 FHWA. Guidance on Traffic Control Devices at Highway-Rail Grade Crossings. 2002 The 2002 version of this publication is available online at: http://safety.fhwa.dot.gov/media/twgreport.htm GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-10 railroad - train frequency, speed and type (passenger, freight, other) highway - functional classification and/or design level of service railroad - FRA class of track and/or high speed rail corridors proximity to other intersections proximity to schools, industrial plants, and commercial areas proximity to rail yards, terminals, passing tracks, and switching operations available clearing and corner sight distance prior accident history and predicted accident history proximity and availability of alternate routes and/or crossing other geometric conditions "Special consideration should also be given to situations where highway-rail crossings are sufficiently close to other highway intersections that traffic waiting to clear the adjacent highway intersection can queue on or across the tracks, and when there are two or more sets of tracks sufficiently close to each other that traffic stopped on one set could result in a queue of traffic across the other" (FHWA, 2002). Highway Operational Requirements FHWA describes the following with respect to highway operational requirements of highway-rail grade crossings (2002): Passive highway-rail grade crossings with a restricted sight distance require an engineering study to determine the safe approach speed based upon available stopping and/or corner sight distance. As a minimum, an advisory speed posting may be appropriate, or a reduced regulatory speed limit might be warranted. Active devices improve highway capacity and level of service near a crossing, particularly where corner sight distances are restricted; however, the effects of such a stop delay will increase as traffic volumes increase which will result in vehicle delay increases. The type of control installed at highway-rail crossings should be evaluated in the context of the highway system classification and level of service. Railroad Operational Requirements "Function, Geometric Design, and Traffic Control - Functional classification is important to both the highway agency and railroad operator. Where the highway intersects a railroad, the crossing, whether grade separated or at-grade, should be designed consistently with the functional classification of the highway or street. These design considerations can also extend to traffic control" (FHWA, 2002). 7.6.4. Traffic Control Devices The purpose of traffic control at highway-rail grade crossings is to permit safe and efficient operation of both vehicle and train traffic over such crossings. Highway vehicles approaching a highway-rail grade crossing should be prepared to yield and stop, if necessary, if a train is at or approaching the crossing. GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-11 Refer to the current FHWA Guidance on Traffic Control Devices at Highway-Rail Grade Crossings and the current FHWA MUTCD for additional information relating to the following types of highwayrail grade crossing traffic control devices: Passive Devices - all highway-rail crossings having signs and pavement markings (if appropriate to the roadway surface) as traffic control devices that are not activated by trains. Passive highway-rail crossing devices include: highway-rail grade crossing (crossbuck) signs, STOP signs, and YIELD signs. Active Devices - all highway-rail grade crossings equipped with warning and/or traffic control devices that gives warning of the approach or presence of a train. Active devices are generally categorized as standard active devices (i.e. flashing-light signals, cantilever flashing-light signals, and automatic gates) and supplemental active devices (i.e. active warning signs with flashers, or active turn restriction signs. Median Separation - the numbers of crossing gate violations can be reduced by restricting driver access to the opposing lanes. The use of median separation devices have resulted in a significant reduction in the number of vehicle violations at crossing gates. Other positive-barrier devices that can be used to prohibit crossing gate violations include: barrier walls, wide raised medians, non-mountable curb islands, mountable raised curb systems, four-quadrant traffic gate systems, and vehicle arresting barrier system - barrier gates. Train Detection Systems - Joint study and evaluation is needed between the highway agency and the railroad to make a proper selection of the appropriate train detection system. Refer to the current FHWA Guidance on Traffic Control Devices at Highway-Rail Grade Crossings for additional information relating to issues specific to train detection systems, such as warning time, system credibility, various types of detection systems, as well as railroad train detection time and approach length calculations. 7.6.5. Alternatives to Maintaining the Crossing Refer to the current FHWA publication, Guidance on Traffic Control Devices at Highway-Rail Grade Crossings, for additional information on the following alternatives to maintaining a highway-rail grade crossing: Crossing Closure "The crossing closure decision should be based on economics; comparing the cost of retaining the crossing (maintenance, crashes, and cost to improve the crossing to an acceptable level if it would remain, etc.) against the cost (if any) of providing alternate access and any adverse travel costs incurred by users having to cross at some other location. Because this can be a local political and emotional issue, the economics of the situation cannot be ignored" (FHWA, 2002). FHWA recommends two documents that provide guidance with regard to political, emotional, and economic ramifications of closing an at-grade highway-railroad crossing: a joint FRA/FHWA publication entitled Highway-Railroad Grade Crossings: A Guide to Crossing Consolidation and Closure (1994), and a March 1995 AASHTO publication, Highway-Rail Crossing Elimination and Consolidation. Grade Separation FHWA notes that the decision to grade separate a highway-rail crossing should be based on long term, fully allocated life cycle costs, including both highway and railroad user costs, rather than on initial construction costs (2002). A 1999 Texas Transportation Institute report entitled Grade Separations-When Do We Separate? provides a stepwise procedure for evaluating the grade separation decision and also describes a rough screening method based on train and roadway vehicular volumes. Evaluation of the feasibility of highway-rail grade separation should consider many factors, including but not limited to: GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-12 o eliminating train/vehicle collisions (including the resultant property damage and medical costs, and liability) o savings in highway-rail grade crossing surface and crossing signal installation and maintenance costs o driver delay cost savings o costs associated with providing increased highway storage capacity (to accommodate traffic backed up by a train) o fuel and pollution mitigation cost savings (from idling queued vehicles) o effects of any "spillover" congestion on the rest of the roadway system o the benefits of improved emergency access o the potential for closing one or more additional adjacent crossings o possible train derailment costs 7.6.6. Crossing Consolidation and New Crossings Crossing Consolidation Guidelines for crossing consolidation can be found in publications such as: FRA/FHWA. Highway-Railroad Grade Crossings, a Guide to Crossing Consolidation and Closure. Federal Railroad Administration/Federal Highway Administration. 1994. FRA/FHWA. Highway-Rail Crossing Elimination and Consolidation, A Public Safety Initiative. National Conference of State Railway Officials. March 1995. Furthermore, GDOT, road authorities, or local governments may choose to develop their own criteria for closures based on local conditions. The FRA and FHWA strongly encourage the use of specific criteria or an approach to consolidating railroad crossings, so as to avoid arbitrarily selecting a crossing for closure. New Crossings Similar to crossing closure/consolidation, consideration of opening a new public highway-rail crossing should likewise consider public necessity, convenience, safety, and economics. Generally, new grade crossings, particularly on mainline tracks, should not be permitted unless no other viable alternatives exist and, even in those instances, consideration should be given to closing one or more existing crossings to offset the additional risks associated with creating an additional crossing. If a new grade crossing is to provide access to any land development, the selection of traffic control devices to be installed at the proposed crossing should be based on the projected needs of the fully completed development. Communities, developers, and highway transportation planners need to be mindful that once a highway-rail grade crossing is established, drivers can develop a low tolerance for the crossing being blocked by a train for an extended period of time. If a new access is proposed to cross a railroad where railroad operation requires temporarily holding trains, only grade separation should be considered. (FRA/FHWA, 2002) GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-13 7.6.7. GDOT At-Grade Highway-Rail Crossing Evaluation Criteria Peabody-Dimmick Formula The Peabody-Dimmick empirical method should be used to evaluate and establish an unadjusted "hazard index" for at-grade highway-railroad crossings. The Peabody-Dimmick Formula (often referred to as the Bureau of Public Roads Formula) is used to determine the expected number of train-vehicle crashes in five years. The formula is: A5 1.28*((V 0.170 *T ) 0.151 / P0.171 ) K Where: A = Expected number of train-vehicle crashes in five years (Unadjusted Hazard 5 Index Rating, as it is not adjusted for school buses) V = Annual Average Daily Traffic (AADT) T = Average Daily Train Traffic P = At-grade Crossing Protection Coefficient K = Balancing factor used to offset variations in empirical data Note: The hazard index only provides an initial approximation of the relative hazard rating of each crossing. While the Peabody-Dimmick formula takes into account the number of daily trains, the vehicular AADT, and a factor for the existing warning devices (protection coefficient); the designer must consider other factors that must be considered before reaching an Adjusted Hazard Index rating for a crossing. These factors include: visibility and sight distances speed (both train and vehicle) number of past train-vehicle crashes at the location number of tracks highway approach grades highway alignment number of highway approach lanes type of terrain nearby intersections condition of existing equipment Based on site-specific information not included in the formula, GDOTs current practice is that the Unadjusted Hazard Index rating produced by the Peabody-Dimmick Formula shall not account for more than 50% of the Adjusted Hazard Index rating. Adjusted Hazard Index Rating The Adjusted Hazard Index (AHI) Rating is the summation of the Unadjusted Hazard Index rating, the Adjustment Factor for School Buses, and the Adjustment for Train-Vehicle Crash history. AHI = A5 + S + A Where: A = Unadjusted Hazard Index Rating 5 S = Adjustment factor for School Buses A = Adjustment for train-vehicle crash history GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-14 Adjustment Factor for School Buses An adjustment factor should be added to the hazard index when a highway route intersects a railroad ,,at-grade. The adjustment factor, S, takes into account the number of school buses traversing the highway-rail crossing during a 24-hour period. S (4 *TPD 8* Buses) 8 10 Where: S = Adjustment Factor for School Buses TPD = Number of Trains per day Buses = Number of Buses per day Note: The adjustment factor for school buses shall only be applied to the Unadjusted Hazard Index rating for highway-rail grade crossings that utilize passive warning devices. If a highway-rail grade crossing utilizes train-activated warning devices, then S = 0. Adjustment Factor for Train-Vehicle Crash History An adjustment factor should be added to the hazard index based on crash history at a highway-rail crossing. The adjustment factor, A, takes into account the number of fatalities, injuries, or property damage only cases when train-vehicle crashes occur. A = 2 * F + 1 * I + 0.5 * PD Where : A = Adjustment Factor for Accidents F = A train-vehicle crash resulting in a fatality I = A train-vehicle crash resulting in an injury PD = A train-vehicle crash resulting in property damage only Note: If a train-vehicle crash results in a fatality, the Adjustment Factor for the train-vehicle crash is 2. (It should be assumed that subject vehicles occupants were injured and the vehicle involved in the incident was damaged). GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-15 Chapter 7 Index At-Grade Crossings Highway-Railroad, 1320 Horizontal Alignment, 14 Vertical Alignment, 14 Driveways, 5 Intersections Geometrics, 23 Highway-Railroad Grade Crossings. See At-Grade Crossings New Intersections, 7 Signalization, 58 Intersections (At-Grade), 120 Sight Distance Stopping Sight Distance, 15 Traffic Signal Modification, 7 Traffic Engineering Study, 7 GDOT Design Policy Manual Revised 06/11/2010 At-Grade Intersections 7-16 Chapter 8 Contents 8. ROUNDABOUTS 1 8.1. Introduction 1 8.2. Roundabout Validation Process 2 8.2.1. Planning Level Assessments 2 8.2.2. Roundabout Feasibility Studies 5 8.2.3. Review of Feasibility Studies 7 8.2.4. Lighting 7 8.2.5. Public Involvement 8 8.3. Design Guidelines 9 8.3.1. Review of Construction Plans 9 8.3.2. Design Vehicle 10 8.3.3. Alignment of Approaches 10 8.3.4. Splitter Islands 10 8.3.5. Pedestrian Design Considerations 10 8.3.6. Bicycle Design Considerations 11 8.3.7. Treatments for High Speed Approaches 11 8.3.8. Drainage 11 8.3.9. Curbing 12 8.3.10. Pavement 12 8.3.11. Staging of Improvements 12 8.3.12. Traffic Control Devices 12 8.3.13. Landscaping 12 8.3.14. Construction 13 8.4. References 13 8.4.1. Primary References 13 8.4.2. Additional References 14 8.5. Definition of Terms 15 8.5.1. Roundabout Physical Features 15 8.5.2. Roundabout Design Elements 17 GDOT Design Policy Manual Revised 06/27/2011 Chapter 8 Contents i List of Tables Table 8.1. Planning-level Estimates of Lane Requirements. 5 List of Figures Figure 8.1. Roundabout Validation Process 3 Figure 8.2. Key Roundabout Physical Features 15 Figure 8.3. Key Roundabout Design Elements 17 GDOT Design Policy Manual Revised 06/27/2011 Chapter 8 Contents ii 8. ROUNDABOUTS 8.1. Introduction A modern roundabout is a type of circular intersection characterized by channelized approaches, a generally circular shape, yield control at entry, and geometric features that create a low-speed environment. They have been demonstrated to provide a number of safety, operational, and other benefits when compared to other types of intersections. Specifically, they have fewer conflict points, lower speeds, provide for easier decision making and have been found to reduce crashes (especially those including fatalities and injuries), traffic delays, fuel consumption, and air pollution. Roundabouts can be categorized into three basic types: mini-roundabouts, single-lane roundabouts, and multilane roundabouts. A detailed introduction to each is provided in Chapter 1 of the National Cooperative Highway Research Program (NCHRP) Report 672, Roundabouts: An Informational Guide. This chapter of the GDOT Design Policy Manual specifically addresses singlelane and multilane roundabouts; for the design of mini-roundabout refer to NCHRP 672. In 2008 FHWA released Guidance Memorandum on Consideration and Implementation of Proven Safety Countermeasures, which identifies roundabouts as one of nine safety countermeasures recognized and supported by FHWA. This document states the following: Roundabouts are the preferred safety alternative for a wide range of intersections. Although they may not be appropriate in all circumstances, they should be considered as an alternative for all proposed new intersections on federally-funded highway projects, particularly those with major road volumes less than 90 percent of the total entering volume. Roundabouts should also be considered for all existing intersections that have been identified as needing major safety or operational improvements. This would include freeway interchange ramp terminals and rural intersections. GDOT also considers roundabouts as the preferred safety and operational alternative for a wide range of intersections on public roads. Specifically, a roundabout shall be considered as an alternative in the following situations: for any intersection being designed on new location or to be reconstructed; for all existing intersections that have been identified as needing major safety or operational improvements; and for all intersections where a request for a traffic signal has been made. A traffic engineering study (TE study) is prepared for all intersections where a signal permit is requested, as required by the GDOT Plan Development Process (PDP). This study includes a planning level assessment as to whether or not a roundabout is expected to perform acceptably. If a roundabout is expected to perform acceptably, a roundabout feasibility study (feasibility study) should be prepared. Each proposal for a roundabout should be developed and evaluated based on the guidelines contained within NCHRP 672, and the guidelines presented in the following sections of this chapter. Additional guidance documents are listed in Section 8.4.1. GDOT Design Policy Manual Revised 03/11/2011 Roundabouts 8-1 8.2. Roundabout Validation Process When considering a roundabout, a variety of alternatives should be evaluated to determine whether or not a roundabout is the most appropriate alternative. These alternatives should include all conventional intersection forms appropriate for the intersection being considered and will often include two-way stop control, all-way stop control, and/or signal control. Chapter 3 of NCHRP 672 provides guidance for comparing the performance of a roundabout to these three forms of intersection control. A signalized intersection is only considered if signal warrants are met, as determined by a TE study. Figure 8.1 presents a validation process which should be used to validate the decision to use a roundabout for a given intersection. This validation process includes: (1) an initial planning level assessment performed as part of a TE study; (2) a roundabout feasibility study; (3) obtaining agreement from local government to participate in lighting costs; and (4) a program of public outreach. The final result of this validation process is a decision to proceed with either a roundabout or conventional (i.e., or nonroundabout) intersection design, or to suspend project development. For stand-alone intersection projects, the roundabout validation process should be completed prior to submission of the concept report for review and approval. Where the intersection is part of a larger project this process should be completed prior to requesting the preliminary field plan review. 8.2.1. Planning Level Assessments The roundabout validation process begins with a planning level evaluation to assess the general suitability of constructing a roundabout at the intersection. This evaluation is performed as part of a TE study, but may be included in the feasibility study. Exhibit 3-1 of NCHRP 672 provides an excellent overview of key planning principles. Listed below are conditions where roundabouts are commonly found to be advantageous over other forms of intersection control. An overview of the primary advantages and disadvantages of roundabouts is presented in Exhibit 2-5 of NCHRP 672. Safety Intersections with historically high crash rates. Roads with a historical problem of excessive speeds. Intersections with more than four legs or with difficult skew angles. Operation Intersections with a high percentage of turning movements and intersections that must accommodate U-turns. Intersections with high traffic volumes at peak hours but relatively low traffic volumes during non-peak hours. Intersections where widening one or more approach may be difficult or cost-prohibitive. While roundabouts may have a larger footprint on the corners of the intersection, the overall space requirement for a roundabout is often less than for a conventional intersection. This is due to the shorter queues generated by a roundabout, thereby requiring less queue storage space on approach legs. Ramp terminal intersections within freeway service interchanges. Roundabouts often make more efficient use of an existing bridge by reducing the queues at each ramp terminal intersection. GDOT Design Policy Manual Revised 03/11/2011 Roundabouts 8-2 Intersections where traffic growth is expected to be high and future traffic patterns are uncertain. A single-lane roundabout can be constructed with allowance for future expansion to a multilane roundabout, and be expanded if and when significant increases in traffic volumes occur. Locations where the speed environment or the number of through lanes of the road changes, for instance, at the fringe of an urban environment. Intersections where signalization cannot provide an adequate level of service. Traffic Control Existing two-way stop-controlled intersections with high side-street delays, particularly those that do not meet signal warrants. Intersections or corridors where traffic calming is a desired outcome of the project. Aesthetics Intersections at a gateway or entry point to a campus, neighborhood, commercial development, or urban area. These may be locations with a need to provide a transition between land-use environments such as between residential and commercial areas. Intersections where community enhancement may be desirable. The presence of any of the following conditions will normally be unfavorable for a roundabout. These conditions do not preclude a roundabout from further consideration, but should be carefully considered when choosing and designing a roundabout. Intersections in close proximity to a signalized intersection where queues may spill back into the roundabout (e.g., coordinated arterial signal systems). Locations with steep grades and unfavorable topography that may limit visibility of the roundabout. Intersections in close proximity to an at-grade railroad crossing. Intersections where an unacceptable delay to the major road could be created. Roundabouts introduce some geometric delay to all through and left turning traffic entering the intersection, including the major street. Heavy pedestrian or bicycle movements in conflict with high traffic volumes that consequently may require pedestrian signals. Table 8.1 can be used to estimate the number of circulatory lanes required for a single- or two-lane roundabout. One and two-lane roundabouts should operate acceptably below these thresholds and are based on Exhibit 3-12 of NCHRP 672. In addition, the opening and design year volumes for traffic entering the roundabout from the major road should normally be less than 90% of the total volume entering the roundabout. Where turning movement data is available, an estimate of the required number of entry lanes at each leg can be obtained using Exhibit 3-14 of NCHRP 672. Sample calculations are provided in Exhibits 3-15 and 4-3. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-4 Table 8.1. Planning-level Estimates of Lane Requirements. No. of Circulatory Lanes ADT1 (design year) % Traffic on Major Road2 (opening & design year) Single-lane < 25,000 < 90 Two-lane < 45,000 < 90 1Based on traffic entering the circulatory roadway, for a four-leg roundabout. A reasonable approximation for a three leg roundabout is 75% of the values shown. 2The volume of traffic entering the roundabout from the major road divided by the total traffic volume entering the roundabout, as a percentage. If traffic volumes are above the thresholds shown in Table 2.1, or if site conditions are unfavorable to a roundabout, an acceptable conventional intersection type may be selected without further evaluation. Nevertheless, a roundabout may still operate better than a conventional intersection and may be carried forward for more detailed consideration as part of a feasibility study. 8.2.2. Roundabout Feasibility Studies A feasibility study should be prepared for all roundabouts. The objective of the feasibility study is to document the decision-making process which demonstrates that a roundabout is (or is not) the most appropriate intersection control form for a specific intersection. The feasibility study also includes a geometric layout of the selected roundabout alternate which can be carried forward to preliminary design. For a stand-alone intersection project, the project concept report may be formatted to incorporate the feasibility study. A well-prepared feasibility study is important for identifying and supporting the selection of a roundabout. Nevertheless, the scope of a feasibility study will vary depending on project conditions and the type and complexity of the proposed roundabout. For example, an intersection of two state routes having a history of injury crashes may not require a detailed cost comparison, considering the significant reduction in injuries that can be expected with a roundabout. On the other hand, the use of a roundabout within a highly urbanized corridor having closely spaced, coordinated signals may require a very detailed feasibility study that goes beyond the scope of what is outlined below. A typical feasibility study can be organized as follows: Section 1, Project Background & Site Conditions: include a summary of the project need, a description of the corridor, and a sketch of existing conditions in the vicinity of the intersection. The sketch should show land-use, access, existing right-of-way, and any physical constraints that may affect the location and design of a roundabout. Section 2, Safety Assessment: include a tabulated analysis of crash data for the three most recent years (at minimum) for which data is available and a comparison to statewide averages. If the purpose of considering a roundabout is to improve the safety at an existing intersection, it is recommended that a crash diagram be prepared. The crash diagram should show the types of crashes and the direction each car was travelling. A roundabout is particularly favorable for addressing crashes involving crossing and turning traffic. Further information regarding safety and roundabouts is presented in Chapter 5 of NCHRP 672. Section 3, Alternate Sketches: include sketches of all design alternates being considered. These can be effectively presented on an aerial photo base map of the intersection and vicinity. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-5 Section 4, Operational Analyses: include operational analyses using peak hour traffic volumes for each design alternate and for opening and design years. The results of each analysis should be presented by lane group in terms of volume-to-capacity ratio, average control delay, level of service, and 95th percentile queue. Based on the results of these analyses the performance of each alternate should be evaluated, and intersection types providing adequate performance identified. Further guidance on evaluating the operational performance of roundabouts can be found in Chapter 4 of NCHRP 672. Analyses should be performed using more than one analysis methodology, to identify a range of expected performance. For example, analyses can be performed using the GDOT Roundabout Analysis Tool to implement the NCHRP Report 572 method and a second method, either the "SIDRA Standard" method using the software package SIDRA Intersection or the empirical method using the software package ARCADY. SIDRA Intersection does not provide a precise implementation of the NCHRP 572 method and should not be used for that purpose. Simulation software packages should be considered where modeling of a network of closely spaced intersection is necessary. Section 5, Cost Comparison: where multiple alternates are expected to provide adequate operational performance, a cost comparison should be prepared. This analysis may be either qualitative or quantitative, but should consider significant benefits relating to safety, operational, and environmental factors and significant costs relating to construction, required right-of-way, operations, and maintenance. Further guidance on estimating benefits and costs can be found in Section 3.7 of NCHRP 672. A detailed benefit-to-cost analysis can be helpful for communicating the benefits of a roundabout to local governments and the public. Section 6, Alternate Selection: include a brief summary of the findings of the above studies (usually in a bulleted form) followed by a recommendation of the most favorable alternate. All assumptions and constraints important to this decision should be included. Section 7, Conceptual Roundabout Design: include a concept level geometric layout of the roundabout and approaches. This layout should include the size and location of the roundabout and the alignment and arrangement of approaches. Major geometric components should be shown including splitter islands, circulatory roadway, truck aprons, center island, and bypass lanes (if required). Geometric and performance checks should include, at minimum - fastest path, design vehicle swept paths, and stopping sight distance for approaches. Other performance checks can be completed during preliminary design (See Section 6.7 of NCHRP 672). A list of the criteria used to develop the selected layout and key dimensions should be provided. It is noted that the selection of the most favorable roundabout configuration and layout may require the development and comparison of multiple roundabout layouts. If a single-lane roundabout is found to be adequate for ten years after the opening year, consideration should be given to constructing a single-lane roundabout. This single-lane roundabout should be designed to be easily retrofitted to a multilane roundabout when traffic volumes grow to warrant the increased capacity. To allow for this future expansion, the ultimate configuration of the multilane roundabout should be defined and the footprint of the constructed roundabout designed to match the footprint of the future multilane roundabout (See Section 6.12 of NCHRP 672). Section 8, Recommendations: briefly state the reasons for selecting the recommended alternate. Any specific requirements or constraints to be considered during preliminary design should be listed and the expected approach for staging briefly described. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-6 8.2.3. Review of Feasibility Studies Feasibility studies prepared by GDOT engineers must be reviewed in accordance with the Department's QC/QA Manual, and studies prepared by consultants in accordance with their own approved QC/QA procedures. Informal reviews by the Office of Design Policy and Support or the Office of Traffic Operations can be requested at any time during the plan development process, by sending an e-mail to [email protected] or by contacting a GDOT roundabout SME directly. Peer review of feasibility studies will be performed for all roundabout projects, unless approval to omit this review is received from the State Design Policy Engineer. Peer reviews are performed by a consultant peer reviewer having extensive experience with the planning, analysis, and design of single-lane and multilane roundabouts. Consultant peer reviewers must be pre-approved by the Office of Design Policy and Support. The objective of the peer review is to verify that a roundabout is the most favorable design alternate and to establish a layout which addresses project needs without unnecessary impacts and costs. Refinement of the layout early in the plan development process has the advantage of allowing for necessary changes to be made without major revisions to construction plans. It is recommended that the feasibility study be peer reviewed prior to the concept team meeting for stand-alone intersection projects where a complex roundabout is proposed. Complex roundabouts include: all multilane roundabouts; and single lane roundabouts having more than four legs, with approach skews less than 60 degrees, and/or closely spaced where the operations of one may have and impact on the operations of another. For other roundabouts, it is recommended that peer reviews should be performed prior to the preparation of preliminary construction plans. Any peer review recommended changes which are not implemented should be coordinated with the Office of Design Policy and Support. If the design engineer proposes not to implement a peer review recommendation, a written response will be submitted along with the peer review report to the Office of Design Policy and Support. If implementation of a peer review recommendation can be (and is to be) delayed until after concept development, written responses along with the peer review report are to be attached to the concept report. 8.2.4. Lighting The lighting of a roundabout has been identified by the Department as having substantial importance to the operational performance and safety of this type of intersection such that special attention should be given to the design and lighting for a roundabout. Therefore, GDOT adopts the recommended illumination levels in Table 1 of the Illuminating Engineering Society DG-19-08, Design Guide for Roundabout Lighting (IES DG-19-08) as a standard for the design of lighting systems for roundabouts. If it is not practical to provide the illumination levels defined by this table, then the decision to select a value or retain an existing condition that does not meet this criteria shall require a comprehensive study by the engineer and the prior approval of a Design Variance from the GDOT Chief Engineer. Both NCHRP 672 and IES DG-19-08 emphasize the safety importance of roundabout lighting for all users of roundabouts. Section 8.1 of NCHRP 672 begins with the following statement: For a roundabout to operate satisfactorily, a driver must be able to enter the roundabout, move through the circulating traffic, and separate from the circulating stream in a safe and efficient manner. Pedestrians must also be able to safely use the crosswalks. To accomplish this, a driver must be able to perceive the general layout and operation of the intersection in time to make the appropriate maneuvers. Adequate lighting should therefore be provided at all roundabouts. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-7 Section 8.2 of NCHRP 672 explains the two main purposes of lighting roundabouts, as follows: It provides visibility from a distance for users approaching the roundabout; and It provides visibility of the key conflict areas to improve users' perception of the layout and visibility of other users within the roundabout. Pedestrians are the most vulnerable users at a roundabout. Thus, an important function of lighting at a roundabout is to ensure that any pedestrian in the crosswalk is visible to vehicles approaching and entering the roundabout. Roadway lighting also provides increased safety to cyclists at the approach to the roundabout where they begin to mix with traffic, and throughout the circulatory roadway where they are integrated into the traffic stream. The guidelines presented in the IES DG-19-08 should be used to develop lighting plans. Lighting plans are normally prepared during the final phase of plan development. NCHRP 672 reproduces Table 1 of IES DG-19-08 as Exhibit 8-1. In order for the design of a roundabout to move forward to detailed design a written commitment must be received from a local government agreeing to share the costs of lighting by funding the energy, operation and maintenance of the lighting system. 8.2.5. Public Involvement A public involvement process should include outreach to local government officials and the local community and should be initiated as soon as practical during concept development. At minimum, a public information open house (PIOH) should be held for all multilane roundabouts and for singlelane roundabouts where there are no other well-functioning roundabouts in the locality or nearby along the corridor. This includes minor projects for which a PIOH may not otherwise be required. In localities where there is little familiarity with roundabouts, it is recommended that a meeting be held with local government officials prior to a PIOH. A roundabout subject matter expert or an individual with considerable knowledge of roundabouts should be present at this meeting. Below are suggested "best practices" for preparing to hold a PIOH or informational meeting. Prepare several large-sized copies of a color display that shows the proposed location and configuration of the roundabout. The display should include aerial photography and property lines. The following may also be included: - proposed pavement markings with lane arrows; - proposed landscaping in the central and splitter islands; and - truck turning paths (on a separate display). In urban areas special attention should be given to minimizing right-of-way impacts. Where possible, use construction easements to reduce project costs and impacts to adjacent properties. Be prepared with a comparison of cost, safety, and operational performance of the roundabout and other alternate intersection forms evaluated as part of a roundabout feasibility study. Specifically, the following information should be available for use during the meeting: - construction cost estimates; - crash history and an assessment roundabout safety benefits; and - operational and signal warrant analyses. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-8 Bring visual aids (e.g. videos, simulations, and brochures) to help familiarize the public with how to drive through a roundabout. Some visual aids are available on GDOT's roundabout website (http://www.dot.state.ga.us/travelingingeorgia/roundabouts/pages/default.aspx) and on FHWA's roundabout website (http://safety.fhwa.dot.gov/intersection/roundabouts/). Additional information regarding public involvement/public education is presented in Section 3.8 of NCHRP 672). 8.3. Design Guidelines This section presents design guidelines which should be used along with NCHRP 672 for the design of roundabouts. Exhibit 6-1 of NCHRP 672 provides an excellent overview of the general design process. A roundabout should be designed with appropriate geometric features to ensure optimal safety and operational performance for users entering, circulating, and exiting the intersection. The following key principles are taken from Section 6.2 of NCHRP 672: provide slow entry speeds and consistent speeds through the roundabout by using deflection; provide the appropriate number of lanes and lane assignment to achieve adequate capacity, lane volume balance, and lane continuity; provide smooth channelization that is intuitive to drivers and results in vehicles naturally using the intended lanes; provide adequate accommodation for the design vehicles; design to meet the needs of pedestrians and cyclists; and provide appropriate sight distance and visibility for driver recognition of the intersection and conflicting users. For multilane roundabouts, below are additional considerations (See Section 6.5 of NCHRP 672): lane arrangements to allow drivers to select the appropriate lane on entry and navigate through the roundabout without changing lanes; alignment of vehicles at the entrance line, into the correct lane within the circulatory roadway; accommodation of side-by-side vehicles through the roundabout (e.g., a truck or bus traveling adjacent to a passenger car); alignment of the legs to prevent exitingcirculating conflicts; and accommodation for all travel modes. Satisfying these key principles involves balancing the sometimes competing needs for safety and operational performance. Accordingly, engineers preparing roundabout designs should be familiar with NCHRP 672 and apply a high level of Quality Control/Quality Assurance (QC/QA) practices throughout the design process. 8.3.1. Review of Construction Plans As with feasibility studies, GDOT prepared construction plans must be reviewed in accordance with the Department's QC/QA Manual, and construction plans prepared by consultants in accordance with their own approved QC/QA procedures. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-9 Prior to the Final Field Plan Review (FFPR), a peer review of the construction plans should be performed. Peer review will normally include all roundabout-related construction plan information. This should include: (1) the horizontal layout; (2) vertical design elements (e.g., typical sections, profiles and grading); (3) drainage; (4) signing and marking plans; (5) landscaping plans; (6) lighting plans; and (7) staging plans. The objective of the peer review is to verify that all design information necessary for construction and operation of the roundabout is provided. Careful consideration is given to design details which can significantly affect performance of the roundabout are current with "best practices" for design and construction. Peer review comments will be added to the FFPR report by Engineering Services and red-lined construction plans provided to the project manager. 8.3.2. Design Vehicle The design vehicle should be an AASHTO WB-67 for all roundabouts on state routes and interchange ramp terminals. The roundabout geometry should accommodate the swept path of the design vehicle tires and body and should be evaluated using a CAD-based vehicle turning path program for each of the turning movements. Buses (BUS-40) in urban areas and single-unit trucks (SU) in rural areas should be accommodated within the circulatory roadway without tracking over the truck apron. For further information on the selection of a design vehicle refer to Section 3.2 of this design policy manual. See also Sections 3.5.4.1, 6.2.4. 6.4.7, and 6.5.7 of NCHRP 672. If needed, roundabouts can be designed with a gated roadway through the central island to accommodate oversized vehicles. 8.3.3. Alignment of Approaches The centerline of the roundabout approaches are often aligned through the center of the roundabout, or be offset to the left of the roundabout center point to enhance deflection of the entry path. Approach alignments offset to the right of the roundabout center point should be avoided unless other geometric features can be applied to produce acceptable fastest path speeds. See Section 6.3.2 of NCHRP 672 for a more in-depth discussion on the alignment of approaches. 8.3.4. Splitter Islands Splitter islands should be incorporated into all roundabouts and should include cut-throughs to accommodate pedestrian traffic. The total length of the raised island should be 100 ft, at minimum. This minimum may be reduced to 50 ft on urban roadways with design speeds less than 45 mph. For high speed approaches splitter islands should be lengthened as described in Section 6.8.5.3 of NCHRP 672. See Sections 6.4.1 and 6.5.5 of NCHRP 672 for more information on the design of splitter islands. 8.3.5. Pedestrian Design Considerations Pedestrians should be considered and accommodated at all roundabout intersections. Pedestrian accommodations should include cut-throughs on splitter islands, two-stage perpendicular crossings, curb ramps and accessibility features such as detectable warning surfaces. Pedestrian activated signals should be considered for multi-lane roundabouts with high pedestrian traffic volumes. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-10 Sidewalks should be set back from the edge of the circulatory roadway with a landscape buffer. Landscape buffers should have a minimum width of 2 ft, with 6 ft being desirable. Stamped and colored concrete should be considered for landscape buffer to assist sight-impaired pedestrians. At singlelane approaches and departures, the pedestrian crossing should be located one car length (approximately 20 ft) away from the inscribed circle. At multilane approaches and departures, the pedestrian crossing should be located one or two car lengths away from the inscribed circle. Further information for the design of pedestrian accommodations for roundabouts is provided in Section 6.8.1 of NCHRP 672. 8.3.6. Bicycle Design Considerations Where bicycle lanes are used on approach roadways, they should be terminated in advance of roundabouts using tapers to merge cyclists into traffic for circulation with other vehicles. For bike routes where cyclists remain within the traffic lane, it can be assumed that cyclists will continue through the roundabout in the travel lane. At multi-lane roundabouts consider providing bicycle ramps to allow bicyclists to exit the roadway onto the sidewalk and travel as pedestrians. Ramps should not normally be used at urban, onelane roundabouts except where the complexity of the roundabout would make circulating like other vehicles more challenging for bicyclists. Further information for the design of bicycle accommodations for roundabouts is provided in Section 6.8.2 of NCHRP 672. 8.3.7. Treatments for High Speed Approaches The primary safety concern in rural locations where approach speeds are high is to make drivers aware of the roundabout with sufficient advance distance to comfortably decelerate to the appropriate speed for entering the roundabout. Where possible, the geometric alignment of approach roadways should be constructed to maximize the visibility of the central island and the shape of the roundabout. Speed reduction treatments should be used for approach roadways where the design speed of the approach is greater than 45 mph. These treatments may include geometric and/or nongeometric techniques. Examples of geometric treatments include the use of horizontal curvature on approaches and the extension of splitter islands upstream of the entry yield line - for a distance equal to the length required to decelerate from the approach roadway design speed to the entry speed of the roundabout. Examples of nongeometric treatments include the addition of successive sets of rumble strips placed in advance of the roundabout, speed reduction markings placed transversely across travel lanes, advance warning signs supplemented by warning beacons, and landscaping of splitter islands to increase their prominence. Further information on treatments for high speed approaches is provided in Section 6.8.5 and 7.4.4 of NCHRP 672. 8.3.8. Drainage Drainage structures should normally be placed on the outer curb line of the roundabout and upstream of crosswalks, but should not be placed in the entry and exit radii of the approaches. Drainage structures located on the outer curb line of the circulatory roadway should be designed to withstand vehicle loading (e.g., Type E, Standard Drop Inlet with Hood shown on GDOT Standard GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-11 Drawing 1019A). Maximum gutter spreads should match the requirements for the approach roadways as outlined in the GDOT manual on the Drainage Design for Highways. Refer to Section 6.8.7 of NCHRP 672 for a discussion of vertical alignment considerations which includes drainage. 8.3.9. Curbing Concrete curb and gutter with a Type 2 curb face should be used along the outside edge of all roundabouts which includes the entry radius, the circulatory roadway, and the exit radius. For rural roadways it is desirable to extend outside curbing along approaches to the length of the required deceleration distance to the roundabout. A Type 2 curb face should also be used for splitter islands. A Type 9 or Type 9a concrete header curb should be used between the truck apron and the circulatory roadway, as specified on GDOT Construction Detail 9032B. Further information on the principles of using curbs on roundabouts Sections 6.8.7.4 and 6.8.8.1 of NCHRP 672. 8.3.10. Pavement Asphalt or dark colored concrete is the recommended material for the circulatory roadway to differentiate it from the concrete truck apron. A proposed pavement design should be prepared for each roundabout and be submitted for review and approval in accordance with the GDOT PDP. Further information on the design of pavements for roundabouts is provided in Section 6.8.8 of NCHRP 672. 8.3.11. Staging of Improvements When projected traffic volumes indicate that a multilane roundabout is required for the design year, the duration of time that a single-lane roundabout can be expected to operate acceptably should be estimated. Consideration should be given to first constructing a single-lane where a single-lane roundabout is expected to be sufficient for ten years or more from the date the roundabout would be open for traffic. To allow for this future expansion, the right-of-way and geometric needs of both the single-lane and multilane roundabout should be defined. For further information refer to Section 6.12 of NCHRP 672. 8.3.12. Traffic Control Devices Traffic control devices for roundabouts shall be in accordance with the 2009 Manual on Uniform Traffic Control Devices. Chapter 7 of NCHRP 672 provides a helpful presentation of the application of traffic control devices to roundabouts. 8.3.13. Landscaping Landscaping plans should be included as a part of the design, especially in the center island to provide visual awareness of the roundabout location. Specifically, landscaping in the central island should adequately block the through sight lines of an approaching driver so that the driver sees the central island. Landscaping within the central island should discourage pedestrian traffic to and through the central island. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-12 Any landscaping that is provided along the perimeter of the central island should consist of low-lying shrubs, grass or groundcover so that stopping and intersection sight distance requirements are maintained for vehicles. Shrubs and columnar growing species may be appropriate within the inner portion of the central island. Consideration should be given to the size and shape of mature plants. Further information on the principles of landscaping for roundabouts is provided in Chapter 9 of NCHRP 672. 8.3.14. Construction Construction time and cost can be reduced by constructing a roundabout while maintaining traffic on an off-site detour, or otherwise outside the footprint of the roundabout (e.g. a roundabout on new location). If this cannot be accomplished and traffic must pass through the work zone, the below is one possible sequence for construction. 1. Install signing and lighting (signing should initially be covered). 2. Maintain traffic on existing roadways. Construct the portion of the roundabout located outside the existing intersection footprint. This should include drainage structures and a portion of the circulatory roadway but not the shoulder outside the circulatory roadway. Construct temporary pavement outside the circulatory roadway for maintaining traffic in the next stage. 3. Remove covered signage and shift traffic from the existing roadways to the temporary circulatory roadway. The intersection should function as a roundabout, the temporary circulatory roadway should be wide enough to accommodate the design vehicle. 4. Construct splitter islands and central island with truck apron. Finish construction of the circulatory roadway and finish any pavement markings. 5. Shift traffic from the temporary circulatory roadway to the final circulatory roadway. 6. Remove temporary pavement and construct shoulders. Complete drainage structures and relocate signing to appropriate locations within the islands. Staging narratives for construction plans will vary considerably from one project to another, and must be specific to the design and constraints of each project. The above is a only brief explanation meant to illustrate a possible sequence of construction. Further information on the stage construction including other staging sequences are presented in Section 10.3 of NCHRP 672. 8.4. References 8.4.1. Primary References For the planning and design of roundabouts refer to the most current edition of the following publications. 2010 Highway Capacity Manual, Transportation Research Board, National Academies of Science, Washington DC, work in progress. Design Guide for Roundabout Lighting, DG-19-08, Roundabout Lighting Committee, Illuminating Engineering Society of North America, New York, NY, June 2009. Highway Capacity Manual, Special Report 209, Transportation Research Board, National Academies of Science, Washington DC, 2000. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-13 Manual on Uniform Traffic Control Devices, Federal Highway Administration, US Department of Transportation, 2009. Roundabouts: An Informational Guide, 2nd Edition, National Cooperative Highway Research Program Report 03-78A, Transportation Research Board, National Academies of Science, Washington, DC, 2010. 8.4.2. Additional References Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities, National Cooperative Highway Research Program Report 03-78A, Transportation Research Board, National Academies of Science, Washington, DC, 2011. Guidance Memorandum on Consideration and Implementation of Proven Safety Countermeasures 5. Roundabouts, Federal Highway Administration, US Department of Transportation, July, 1, 2009. Highway Design Handbook for Older Drivers and Pedestrians, Publication No. FHWA-RD-01103, Federal Highway Administration, US Department of Transportation, May 2001. Mini-Roundabout Technical Summary, Report FHWA-SA-10-007, Federal Highway Administration, US Department of Transportation, Feb. 2010. Pedestrian Access to Modern Roundabouts: Design and Operational Issues for Pedestrians Who are Blind, US Access Board. Roundabouts in the United States, NCHRP Report 572, National Cooperative Highway Research Program, Transportation Research Board, National Academies of Science, Washington DC, 2007. Roundabout Technical Summary, Report FHWA-SA-10-006, Federal Highway Administration, US Department of Transportation, Feb. 2010. Signalized Intersections: An Informational Guide, Publication No. FHWA-HRT-04-091, Federal Highway Administration, US Department of Transportation, August 2004. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-14 8.5. Definition of Terms Figures 8.2 and 8.3 illustrate key roundabout physical features and design elements. These figures were modified from the report, Technical Memorandum: Planning-Level Guidelines for Modern Roundabouts prepared by the Center for Transportation Research and Education at Iowa State University [2008]. Definitions for key terms are provide below each figure and most are taken or adapted from either the above report or NCHRP 672. 8.5.1. Roundabout Physical Features Figure 8.2. Key Roundabout Physical Features Apron (or Truck Apron) the mountable portion of the central island adjacent to the circulatory roadway. Used in some roundabouts to accommodate the wheel tracking of large vehicles. Bike Ramp Allows for bicyclists to exit the traveling lane to the sidewalk and use the crosswalk as a pedestrian would. It is recommended that only experienced bicyclists be encouraged to use the roadway and that novice riders exit the roadway, dismount their bikes and use the sidewalk and crosswalks. [See Section 6.8.2.2 of NCHRP 672 for further reference.] Central Island (or Center Island) the raised area in the center of a roundabout around which traffic circulates. The central island does not necessarily need to be circular in shape. In the case of mini-roundabouts the central island is traversable. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-15 Circulatory Roadway the curved path used by vehicles to travel in a counterclockwise fashion around the central island. Entrance Line (or Yield Line) a pavement marking used to mark the point of entry from an approach into the circulatory roadway and generally marked along the inscribed circle. Entering vehicles must yield to any circulating traffic coming from the left before crossing this line into the circulatory roadway. Landscaping Buffer (or Landscaping Strip) Landscape strips separate vehicular and pedestrian traffic and assist with guiding pedestrians to the designated crossing locations. This feature is particularly important as a wayfinding cue for individuals who are visually impaired. Landscape strips can also significantly improve the aesthetics of the intersection. Lighting Provides illumination for all potential conflict areas, including the beginning of the splitter island, all crosswalks, and entries and exits to the circulatory roadway. Also, provides illumination to make the roundabout visible from a distance, for users approaching the roundabout. Mini-roundabout small roundabouts used in low-speed urban environments. The central island is fully mountable, and the splitter islands are either painted or mountable. [See Exhibit 1-10 of NCHRP for a layout showing the features of a typical mini-roundabout.] Modern Roundabout a term used to distinguish newer circular intersections, conforming to the characteristics of roundabouts, from older-style rotaries or traffic circles. [See Section 1.2 of NCHRP 672 for a detailed explanation of the characteristics of a modern roundabout and comparison to older types of circular intersections.] Multilane roundabout a roundabout that has at least one entry with two or more lanes, and a circulatory roadway that can accommodate more than one vehicle travelling side-by-side. [See Exhibit 1-16 for examples of multilane roundabouts.] Outside Curbing Non-mountable curb defining the outside edge of the pavement on each approach, around the circulatory roadway, and continuing outside the adjacent exit. Curbs improve delineation and discourage corner cutting, which helps to maintain lower speeds. Ideally begins at the deceleration point on each approach. [See Section 6.8.5.2 of NCHRP 672 for further reference.] Right-Turn Bypass Lane a lane provided adjacent to, but separated from, the circulatory roadway, that allows right-turning or through movements to bypass the roundabout. Also known as a right-turn slip lane. [See Section 6.8.6 of NCHRP 672 for further reference.] Sidewalk used in urban areas to accommodate pedestrians. Splitter Island the raised or painted area on an approach, used to separate entering from exiting traffic, deflect and slow entering traffic, and provide storage space for pedestrians crossing the intersection approach in two stages. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-16 8.5.2. Roundabout Design Elements Figure 8.3. Key Roundabout Design Elements Approach Width the width of the roadway used by approaching traffic upstream of any changes in width associated with the roundabout. The approach width is typically no more than half the total roadway width. Circulatory Roadway Width the width between the outer edge of the circulatory roadway and the central island, not including the width of any apron. Conflict Point a location where the paths of two vehicles, or a vehicle and a bicycle or pedestrian, merge, diverge, cross, or queue behind each other. [See Exhibits 5-1 and 5-2 of NCHRP 672 for illustration of vehicle conflict points at 3- and 4-leg roundabouts and conventional intersection.] Deflection the change in trajectory of a vehicle imposed by geometric features of the roadway. Entry deflection helps control vehicle speeds and discourages wrong-way movements on the circulatory roadway. [See Exhibit 6-10 of NCHRP 672 for a comparison on entry alignments with and without deflection.] Entry Flare the widening of an approach to multiple lanes to provide additional capacity at the yield line and storage. [See Exhibit 1-8(e) of NCHRP 672 for an example of an entry flare for a multilane roundabout and Section 6.5.2 of the same report for further reference.] Entry Speed the speed a vehicle is traveling as it crosses the yield line. GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-17 Entry Width the width of the entry where it meets the inscribed diameter, measured perpendicularly from the right edge of the entry to the intersection point of the left edge line and the inscribed circle. Fastest Path The fastest path allowed by the approach and roundabout geometry determines the negotiation speed for that particular movement into, through, and exiting the roundabout. It is the smoothest, flattest path possible for a single vehicle, in the absence of other traffic and ignoring all lane markings. [See Section 6.7.1 of NCHRP 672 for a detailed presentation. Exhibit 6-46 for of NCHRP 672 illustrates the five critical path radii that must be checked for each approach.] Geometric Delay the delay caused by the alignment of the lane or the path taken by the vehicle on a roadway or through an intersection. [See Section 4.5.8 of NCHRP 672 for further reference.] Inscribed Circle Diameter the basic parameter used to define the size of a roundabout, measured between the outer edges of the circulatory roadway. It is the diameter of the largest circle that can be inscribed within the outline of the intersection. Locking stoppage of traffic on the circulatory roadway caused by queuing backing into the roundabout from one of the exits, resulting in traffic being unable to enter or circulate. Natural Path The path an approaching vehicle will take through a multi-lane roundabout, assuming traffic in all lanes. The speed and orientation of the vehicle at the yield line determines the natural path. [See Section 6.7.2 of NCHRP 672 for further reference.] Path Alignment a roundabout should naturally align entering lanes into their appropriate lane within the circulatory roadway and then to the appropriate lanes on the exit. [See Sections 3.5.4.2 and 6.2.3 of NCHRP 672 for further reference.] Roundabout Capacity the maximum number of entering vehicles that can be reasonably expected to be served by a roundabout during a specified time period. Vehicle Path Overlap - Path overlap occurs on multi-lane roundabouts when the natural path through the roundabout of one vehicle overlaps that of another vehicle. Occurs most commonly on the approach when a vehicle in the right lane cuts off a vehicle in the left lane as the vehicle enters the circulating lane. [See Exhibits 6-28 and 6-33 of NCHRP 672 for illustrations of entry and exit vehicle path overlap, and Section 6.2.3 of the same report for a discussion of appropriate path alignment.] View Angle - View angle is measured as the angle between a vehicle's alignment at the entrance line and the sight line required according to intersection sight-distance guidelines. The intersection angle between consecutive entries must not be overly acute in order to allow drivers to comfortably turn their heads to the left to view oncoming traffic from the immediate upstream entry. [See Section 6.7.4 of NCHRP 672 for further guidance.] GDOT Design Policy Manual Revised 06/27/2011 Roundabouts 8-18 Chapter 9 Contents 9. BICYCLE & PEDESTRIAN ACCOMMODATIONS 2 9.1. Overview 2 9.1.1. Americans with Disabilities Act 2 9.1.2. Definition of Accommodations 2 9.1.3. Incremental Approach 2 9.2. Typical Users & Needs 2 9.2.1. Pedestrians 2 9.2.2. Bicyclists 3 9.2.3. Non-Motorized Needs and Volumes 3 9.3. Bicycle Route Networks 4 9.4. Warrants for Accommodation 6 9.4.1. Pedestrian Warrants 6 9.4.2. Bicycle Warrants 6 9.4.3. Exclusions 7 9.5. Facility Design 7 9.5.1. Pedestrian Facility Design 7 9.5.2. Bicycle Facility Design 11 9.5. Work Zone Accessibility 13 List of Figures Figure 9.1. Examples of designated Bicycle Routes: 4 Figure 9.2. Georgia Statewide Bicycle Route Network 5 Figure 9.3. Illustrations of Pedestrian Facility Design 10 Figure 9.4. Illustration of Bike Lane Design along Rural and Urban Roadways 12 GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-1 9. BICYCLE & PEDESTRIAN ACCOMMODATIONS 9.1. Overview Bicycle and pedestrian accommodations are incorporated into transportation projects as a means to improve the safety and mobility of non-motorized users. The result should be a system that allows choice among both motorized and non-motorized modes of transportation. This Bicycle and Pedestrian Accommodations policy is based on principles from the Georgia DOT Pedestrian and Streetscape Guide (2003), the AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities (2004), the AASHTO Guide for the Development of Bicycle Facilities, and the Public Right of Way Accessibility Guidelines (PROWAG) developed under the umbrella of the United States Access Board and the Americans with Disabilities Act of 1990 (ADA). The latest PROWAG can be downloaded at: http://www.access-board.gov/prowac/draft.htm. 9.1.1. Americans with Disabilities Act The ADA was enacted by the U.S. Congress and signed into law on July 26, 1990, and later amended with changes effective January 1, 2009. The ADA is a wide-ranging civil rights law that prohibits, under certain circumstances, discrimination based on disability. ADA design guidelines for accessible buildings and facilities are published in the ADA Accessibility Guidelines (ADAAG). ADA design guidelines for accessible public rights-of-way are published in the PROWAG. 9.1.2. Definition of Accommodations An accommodation is here defined as any facility, design feature, operational change, or maintenance activity that improves pedestrian and bicycle travel. The type of accommodation may vary by location and the needs of typical users, but the safety and accessibility of all modes should be considered in every situation. Accommodations may include the provision of: bike lanes, shared-lane markings, or paved shoulders; sidewalks or shared-use paths; intersection and midblock treatments such as marked crosswalks, signs, lighting, and accessible features; and/or other treatments as necessary. 9.1.3. Incremental Approach Bicycle and pedestrian accommodations are included as components of larger transportation projects. This strategy is a long-term incremental approach to developing a statewide network. All necessary segments being consistently designed and implemented will provide for the safe and efficient movement of bicyclists, pedestrians, and motorists throughout the state. 9.2. Typical Users & Needs Pedestrians and bicyclists are often grouped together when referring to non-motorized users. Both users generally travel at the far right or outside of the roadway, are generally slower than adjacent motor vehicles, and are more influenced by their immediate surroundings. Since both non-motorized modes travel under their own power and are more exposed to the elements, both often prefer direct routes or shortcuts to minimize their effort and time. However, there are significant differences between both pedestrians and bicyclists and within each of the two groups. 9.2.1. Pedestrians All transportation trips begin or end with walking. Many pedestrians choose to walk for convenience, personal health, or out of necessity. They often prefer greater separation from the roadway, require additional time to cross roadways, and are the most vulnerable of all roadway users. Pedestrians will GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-2 often seek to minimize travel distance, choosing direct routes and shortcuts even when facilities are not provided. Walking trips are often combined with public transit for traveling longer distances, making consideration of accessibility to transit stations and stops a critical factor. Pedestrians also include children, senior citizens, or people with physical disabilities; these groups may require additional design considerations. 9.2.2. Bicyclists Bicyclists utilize pubic roadways for most trips and are therefore subject to vehicular laws. Therefore, the bicycle facility should be designed to encourage cycling behavior that is as predictable as possible when interacting with vehicular traffic. Bicycling trips serve both utility and recreation purposes, often in the same trip. Utilitarian and commuter cyclists will generally choose whichever roadway provides for the most direct, safe and comfortable travel to their destinations. Younger, less experienced or recreational riders will typically choose routes for comfort or scenery and may feel more comfortable on separated facilities. Bicycle facilities should be context sensitive and should be selected based on the characteristics of the road corridor, the expected needs of typical users, the accessibility of the facility to area destinations, and other considerations. There are two general types of bicycle facilities; on-road facilities including bike lanes or shared lanes; and off-road facilities such as shared-use paths, cycle tracks, or greenway trails. On-road facilities allow cyclists to circulate with traffic, allow easier access to destinations, and help cyclists behave more predictably. Off-road facilities may allow greater separation from high-speed traffic but need careful consideration at driveways, intersections, and constrained areas. These two facility types are not interchangeable and careful examination of their application should be conducted on a case-by-case basis. 9.2.3. Non-Motorized Needs and Volumes Planning studies for bicycle and pedestrian travel normally consider the number of users, their typical needs, and significant barriers to travel. This includes measuring current and projecting future travel, evaluating existing conditions, and identifying constraints and opportunities. Typical planning tools may include non-motorized traffic counts, Bicycle or Pedestrian Level of Service formulas, Latent Demand Scores, user surveys, and public input; these tools all help establish user levels, destinations, and facility needs above the most basic routine project accommodations. The degree of non-motorized users and their needs should be determined during the project planning or concept development phase. Defining the degree of non-motorized use and their needs will often require local input and for most projects can be accomplished during the initial concept meeting, reconnaissance of the project area, and meetings with local officials and stakeholders. PIOH meetings are also a useful venue for obtaining this information. The findings and decisions of investigations relating to non-motorized users should be documented in the concept report as part of the "Need and Purpose" statement. This information may be qualitative in nature but must be sufficient for use by the design phase leader to evaluate the bicycle and pedestrian warrants presented in Section 9.4 of this chapter. The evaluation of warrants should be included as a separate section in the concept report. If the project is expected to adversely impact existing bicycle or pedestrian accommodations, this should also be noted. GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-3 9.3. Bicycle Route Networks Roads and bikeways form a network of bicycle routes that facilitate travel for bicyclists by connecting metropolitan areas or regional destinations of important scenic, historic, cultural, and recreational value. An important role of planning is to help ensure that bicycle routes provide for reasonably direct travel. An important role of design is to help reduce other impediments (which discourage bicycle travel) by incorporating bicycle provisions into construction projects. Consequently, rural cycling routes and longdistance routes routinely consider the populations of the areas they connect rather than the populations along the actual route. The Georgia DOT maintains a network of cross-state bicycle routes to facilitate long-distance bicycle travel in Georgia (see Figure 9.1., Georgia Statewide Bicycle Route Network). Regional planning commissions and local governments in Georgia have developed bicycle route networks which connect destinations within regions or facilitate local trips. These routes consist primarily of on-road facilities (such as paved shoulders, bicycle lanes, or shared lanes) and way finding or cautionary signs. Local, regional, and state bike routes are on file in the State Bicycle and Pedestrian Coordinator's office in the Office of Planning. Routes identified as part of the Georgia Statewide Bicycle Route Network shall, at a minimum, comply with the basic bicycle accommodations outlined below: all long-distance bicycle routes will meet the criteria for an approved numbered bicycle route system established by the American Association of State Highway and Transportation Officials (AASHTO), Manual on Uniform Traffic Control Devices (MUTCD), and GDOT guidelines; Georgia state bicycle routes will be coordinated with neighboring states to ensure consistency for regional or national networks and allow for inter-state bicycle travel; and long-distance bicycle routes should include the installation of bicycle route number signs and way finding or cautionary signs where necessary. While bicycle routes provide information to traveling cyclists, cyclists are allowed to ride on any road legally open to bicycles regardless of the presence or absence of specific bicycle accommodations or designations. Figure 9.1. Examples of designated Bicycle Routes: Scenic Byway, North Georgia Bike Lane, Sugarloaf Parkway, Gwinnett County GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-4 Figure 9.2. Georgia Statewide Bicycle Route Network GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-5 9.4. Warrants for Accommodation The Georgia Department of Transportation has established the following standards and guidelines to ensure that bicycle and pedestrian accommodations are provided on all appropriate infrastructure projects where pedestrians and bicyclists are permitted to travel. Warrants for bicycle and pedestrian accommodations will be evaluated as part of project concept development, and documented in the concept report. If it is not practical to comply with the criteria below denoted as "standards", then agency approval and documentation will be required by formal Design Variance before the accommodation can be modified or excluded from the project. To obtain a Design Variance, a comprehensive study and formal request shall be submitted using the format and procedures outlined in the GDOT Plan Development Process (PDP). Examples of cases where bicycle and pedestrian accommodations may be excluded from projects are provided in Section 9.4.3, Exclusions. 9.4.1. Pedestrian Warrants Standards Pedestrian accommodations shall be considered in all planning studies and included in all reconstruction, new construction, and capacity-adding projects that are either located in an urban area (typically where curb and gutter is provided) or are located in areas with any of the following conditions: on corridors with pedestrian travel generators and destinations (i.e. residences, commercial locations, schools, public parks, etc), or areas where such generators and destinations can be expected within the projected lifespan of the project; where there is evidence of pedestrian traffic (e.g. worn path along roadside); on corridors served by fixed-route transit in urban and suburban areas; where there is an occurrence of "walking along the roadway" type crashes; and where a need is identified by a local government through a planning study and public involvement process. Guidelines Pedestrian accommodations should be considered in all planning studies and included in all reconstruction, new construction, and capacity-adding projects that are located in areas with any of the following conditions: within close proximity (i.e. 1 mile) to any school, college or university; and any location where engineering judgment or planning analysis determines a need. As part of Preventative Maintenance (PM) projects and Resurfacing, Restoration, or Rehabilitation (3R) projects, improvements and/or repairs to curb ramps should be assessed on a case-by-case basis. The Office of Maintenance will determine the eligibility for improvements and/or repairs to curb ramps at the formal field plan review. 9.4.2. Bicycle Warrants Standards Bicycle accommodations shall be considered in all planning studies and included in all reconstruction, new construction, and capacity-adding projects that are located in areas with any of the following conditions: where there is an existing bicycle facility in place (including bike lanes, paths, shoulders, wide curb lane, and/or signage); if the project is on a state, regional, or local bike route; and where there is a demonstrated need, with bicycle travel generators and destinations (i.e. urban areas, residential neighborhoods, commercial centers, schools, colleges, public parks, etc), or areas where such generators and destinations can be expected within the projected lifespan of the project. GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-6 Guidelines Bicycle accommodations should be considered on projects that are located in areas with any of the following conditions: within close proximity (i.e. 2 miles) to any school, college or university; where a project will provide connectivity between two or more existing bikeways; where a local bike route is identified by a local government through a planning study; along bicycle routes that connect metropolitan areas and regional destinations; on resurfacing projects in urban areas, the Department may consider restriping the roadway and narrowing travel lanes to provide additional shoulder width or wide curb lane. Restriping will be considered where space is available and where there is no significant history of sideswipe crashes. The Office of Maintenance will coordinate with the Office of Planning and Office of Traffic Operations to define an appropriate crash threshold for determining eligibility for restriping on a project-by-project basis; on projects where a bridge deck is being replaced or rehabilitated with Federal financial participation, and where bicycles are permitted to operate at each end of the bridge, the bridge deck may be replaced or rehabilitated to provide safe bicycle accommodations; and any location where engineering judgment or planning analysis determines a need. 9.4.3. Exclusions Bicycle and pedestrian accommodations are excluded from routes that have been designated as "Full Access Control" such as freeways and interstate highways." A sidewalk may be excluded on side road tie-ins where there is no existing sidewalk and the additional widening of shoulders for sidewalk would result in excessive impacts as determined by the design team on a case-by-case basis. Sidewalks are not required in rural areas where curb and gutter is placed at the back of the useable shoulder for the purpose of reducing construction limits. Either of the following conditions may be considered justification for a Design Variance to exclude bicycle and pedestrian facilities: 1. projects where the cost of providing bicycle and pedestrian facilities would be excessively disproportionate to the need or probable use. Excessively disproportionate is defined as exceeding twenty percent (20%) of the total cost of the project; and 2. bridge projects where the existing width will provide adequate shoulders (at least 4-ft. of smooth pavement) for non-motorized use. 9.5. Facility Design 9.5.1. Pedestrian Facility Design The Georgia DOT has compiled the following design criteria as recommended dimensions when designing sidewalk and pedestrian facilities in Georgia. The criterion was developed with reference to the PROWAG developed under the umbrella of the United States Access Board and the ADA. In some cases, GDOT provides more specific and selective criteria relating to the design of sidewalks. If it is not practical to comply with the following GDOT criteria, then the designer shall, at a minimum, comply with the criteria published in the PROWAG. If an engineer determines that the nature of an existing facility makes it technically infeasible to comply fully with the accessibility standards published in the PROWAG, then the design or alteration shall provide accessibility to the "maximum extent feasible". The approval of a Design Variance from the GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-7 GDOT Chief Engineer will be required before a design or alteration can be retained or incorporated into a project that does not comply with the criteria published in the PROWAG. For design options involving pedestrian facilities in urban areas, GDOT recommends the report "Accessible Public Rights-of-Way Planning and Design for Alterations", published by the Public Rightsof-Way Access Advisory Committee (PROWAAC). The report is located on-line at: http://www.accessboard.gov/prowac/alterations/guide.htm. Location of Sidewalk Sidewalks are typically provided along urban shoulders, wherever curb and gutter is utilized along the outside edges of pavement of the mainline. See Chapter 6.7 Border Area (urban shoulder) of this Manual for a more complete definition of an urban shoulder. Width of Sidewalk GDOT recommends the minimum width of sidewalk be 5-ft of clear unobstructed space. A 5-ft sidewalk width should allow adequate space for two wheelchairs to pass without conflict. Higher pedestrian usage may warrant the use of wider sidewalks. The PROWAG (R301.3) specifies that "walkways in pedestrian access routes that are less than 5-ft in clear width shall provide passing spaces at intervals of 200-ft maximum. Pedestrian access routes at passing spaces shall be 5-ft wide for a distance of 5-ft" When right-of-way is limited at intersections, the designer should be careful not to violate this requirement by placing a strain pole or pedestrian signal head in a way that would reduce this 5-ft x 5-ft area. Buffer Space The buffer space is defined as the area between the back of curb and edge of sidewalk. The buffer space provides important safety and comfort benefits for walkers as well as allows room to place utilities or street furniture without obstructing the pedestrian travel way. GDOT recommends a 6-ft wide buffer space between the back of curb and the sidewalk. If a roadway has multiple driveways, a 6-ft buffer space will provide the offset required to connect the sidewalk perpendicular to the back of a standard concrete valley gutter driveway. The minimum buffer space between the back of curb and sidewalk should be at least 2-ft wide, to provide a degree of separation between pedestrian and vehicle, and to allow for utilities. A minimum 2ft wide grass or paver strip is preferred because it provides a color contrast which assists visually impaired pedestrians to better distinguish between the sidewalk and roadway. A minimum 2-ft wide buffer also provides some protection from overhanging objects from vehicles, and also creates a psychological barrier, enhancing pedestrian comfort. Where right-of-way constraints will not permit a 2-ft buffer width, sidewalk may be constructed adjacent to the back of curb. For example, this may occur in Central Business Districts or where buildings are adjacent to the right-of-way. Cross-Slope The maximum allowable sidewalk cross-slope shall not exceed 2.0% (PROWAG R301.4.1). Longitudinal Slope The longitudinal slope (grade) of a sidewalk shall not exceed the general grade established for the adjacent street or roadway (PROWAG R301.4.2). In cases where sidewalk alignment deviates from the adjacent roadway, the longitudinal slope of the sidewalk shall not exceed 8.3% (PROWAG 303.2.1.1). GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-8 Curb Ramps The ADA requires accessible curb ramps be included on pedestrian facilities. Ramp profile shall have a running slope between 5 percent minimum and 8.3 percent maximum (PROWAG R406.2). The ramp should be placed in line with pedestrian flow and crosswalks, and the edges of a diagonal curb ramp must be parallel to the direction of pedestrian flow. The bottom of diagonal curb ramps shall have 48 in. minimum clear space between the curb line and the vehicle traveled way line. Refer to GDOT Construction Standards and Details, Construction Details A-1, A-2, A-3, and A-4 for additional information regarding the typical location and design of sidewalks and curb ramps. Sidewalk Surface The surface of the pedestrian access route shall be firm, stable and slip resistant. Surface discontinuities shall not exceed " maximum vertical or horizontal (PROWAG R301.5.2). In situations where existing sidewalk will be retained, vertical discontinuities between in. and in maximum shall be beveled at 1:2 minimum. The bevel shall be applied across the entire level change. In situations where existing sidewalk will be retained, the project must repair/replace areas of sidewalk that has heaved (vertical) more than in., or if there are more than in. gaps (horizontal) in the sidewalk. Detectable Items for the Impaired Detectable warnings are devices that alert a visually impaired person that they are entering or exiting a potentially hazardous area. All wheelchair ramps shall incorporate a detectable warning surface (see GDOT Detail A4). The minimum width of the detectable warning surface is the width of the curb ramp exclusive of flared sides (R304.1.4). Detectable audible warning systems should be used where a need has been determined. Crosswalks Crosswalk design, placement, and the selection of additional safety treatments (where necessary) should meet GDOT's most recent guidance located in Section 12.2.3 of the GDOT Signing and Marking Design Guidelines and in GDOT Construction Details. Bridges A typical sidewalk width across a bridge in an urban area is 6-ft without a buffer space between the back of curb and sidewalk. Therefore, the width of the sidewalk should transition from the roadway cross section to the bridge cross section before the approach slab. This should also include eliminating the buffer space in advance of the bridge. When sidewalk is tapered to match the bridge shoulder, this is typically done in an area 50-ft to 100-ft in advance of the bridge. Where guardrail is used on the bridge approaches, the sidewalk transition should follow the guardrail offset transition. GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-9 Figure 9.3. Illustrations of Pedestrian Facility Design GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-10 9.5.2. Bicycle Facility Design GDOT adopts the design guidance published in the AASHTO Guide for the Development of Bicycle Facilities. Design consistency with local or regional bicycle plans should be considered wherever possible. There are three types of bicycle facilities commonly designed by GDOT. 1. On-Street Bicycle Facility preferred by GDOT where practical, an on-street bicycle facility has a designated one-way "bike lane" with painted stripe and symbols directly adjacent to the travel lane for preferential or exclusive use by bicyclists. On-street bicycle facilities are generally preferred for commuter cyclists because they allow bicyclists to travel with the flow of traffic and have a minimal amount of conflict points with pedestrians and driveways. Consistent with AASHTO, GDOT has adopted 4-ft as the typical "bike lane" width for both rural and urban type roadways. GDOT recommends the dimensions indicated below. On rural roadways, the 4-ft bike lane is incorporated into the overall width of paved shoulder to include a 16-in rumble strip offset 12-in from the traveled way. The shoulders are designed with a gap pattern rumble strip to allow bicyclists to smoothly enter and exit the bike lane. Refer to Ga. Construction Detail S-8 for additional information regarding the design of bike lanes and rumble strips on paved shoulders. On urban roadways with curb & gutter, the 4-ft bike lane is developed between the traveled way and gutter. The bike lane does not include the gutter width. The designer should note, if the space to the right of the traveled way stripe is less than 4-ft wide, the route cannot be signed or marked as a "bike lane" facility and will be referred to as a shoulder (refer to design of signed shared roadway facility). 2. Signed Shared Roadway Facility where it is not practical to design a designated minimum 4-ft "bike lane", a signed shared roadway facility may be considered. A signed shared roadway facility requires that vehicles and bicycles share the travel lanes of the roadway. Signed shared roadways are identified by signing as a preferred bike route. A signed shared roadway facility should provide a wide outside lane or paved shoulder to accommodate bicycle travel. The additional shoulder width is especially desirable if vehicle speeds exceed 50 mph and the percentage of large vehicles is high. The measurement of usable shoulder width should not include the width of a gutter pan. 3. Shared-Use Paths a paved or unpaved facility physically separated from motorized vehicular traffic by an open space or barrier; either within the highway right-of-way or within an independent right-of-way. Shared-use paths (also referred to as multi-use paths) are used by bicyclists, pedestrians, skaters, joggers, or other non-motorized users. Shared-use paths are considered offroad transportation routes for bicyclists and others and serve as a necessary extension or supplement to on-road bicycle facilities. Shared-use paths should not be considered a substitute for on-street improvements. Bicycle safe drop-inlet grates are required for all roadways that meet the warrants for bicycle accommodations defined in this policy. GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-11 Figure 9.4. Illustration of Bike Lane Design along Rural and Urban Roadways GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-12 9.5. Work Zone Accessibility For pedestrian accessibility requirements during construction see GDOT Special Provision, Section 150.02 K. Pedestrian Considerations. The current GDOT SP 150 Traffic Control is located on the Department's website at the following address. http://www.dot.ga.gov/doingbusiness/theSource/special_provisions/shelf/sp150.pdf GDOT Design Policy Manual Revised 3/1/2011 Bicycle & Pedestrian Accommodations 9-13 Chapter 11 Contents 11. OTHER PROJECT TYPES 1 11.1. Preventative Maintenance (PM), Resurfacing, Restoration, or Rehabilitation (3R), and Reconstruction Guidelines for Federal Aid Projects 1 11.1.1. Procedures and Guidelines 2 11.1.2. Controlling Criteria for Non-Interstate Systems (GDOT 3R Standards) 5 11.1.3. Other Design Considerations for 3R Projects (GDOT 3R Standards) 8 11.2. Special Design Considerations for Other Project Types 10 11.2.1. Bridge Fencing Projects 10 11.2.2. Bridge Jacking Projects 11 11.2.3. Intelligent Transportation System (ITS) Projects 11 11.2.4. Signing & Marking Projects 11 11.2.5. Traffic Signal Projects 12 11.2.6. Noise Abatement Projects 12 11.3. Design Elements for Other Project Types 12 11.3.1. Survey Requirements 12 11.3.2. Construction Plans 14 11.3.3. Pavement Design 14 11.3.4. Environmental 14 11.3.5. Earthwork 14 11.3.6. Drainage 15 11.3.7. Guardrail and/or Barrier 15 11.3.8. Erosion Control Plans 15 11.3.9. Traffic Signal Plans 15 11.3.10. Signing & Markings 15 11.3.11. Utilities 15 11.3.12. Traffic Control Plans 15 Chapter 11 Index 16 GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Chapter 11 Contents i List of Figures Figure 11.1. PDP Process for PM, 3R, and Reconstruction Projects List of Tables Table 11.1. Geometric and Safety Guidelines for 3R, PM, and Reconstruction Projects Table 11.2 Usable Shoulder Width for Two Lane Roadways Table 11.3 Minimum Bridge Widths for Non-interstate Highways Rural Sections (2-Lanes) Table 11.4. Minimum Bridge Widths for Non-interstate Highways Multilane Rural Sections Table 11.5. Minimum Bridge Widths for Local Roads and Streets (Rural Sections) (1) Table 11.6. Horizontal Clearance Table 11.7. Horizontal Alignment for Existing Features not meeting 3R Guidelines 3 4 5 5 6 6 6 7 GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Chapter 11 Contents ii 11. OTHER PROJECT TYPES The Georgia Department of Transportation (GDOT) Road Design Policy Manual is primarily written to provide guidance for the preparation of construction documents for projects involving the new construction or major reconstruction of state roadways. Guidelines, design policies, and practices discussed in this chapter address the following other types of projects: preventative maintenance (PM); roadway resurfacing, restoration, or rehabilitation (3R); and reconstruction projects bridge fencing and bridge jacking projects intelligent transportation system (ITS) projects signing and pavement marking projects traffic signal projects guardrail and/or barrier projects The policies in this manual apply to permanent construction of Georgia roads and highways, and different controls and criteria may be applicable to temporary facilities. 11.1. Preventative Maintenance (PM), Resurfacing, Restoration, or Rehabilitation (3R), and Reconstruction Guidelines for Federal Aid Projects The purpose of this Section is to provide design guidelines and procedures that cover GDOT's Pavement Maintenance and Resurfacing, Restoration, or Rehabilitation Program. This program includes preventative maintenance (PM); resurfacing, restoration, or rehabilitation (3R); and reconstruction projects per the agreement between the GDOT and the Federal Highway Administration (FHWA). PM projects are defined as the planned strategy of cost effective treatments to an existing roadway system and its appurtenances that preserves the system, retards future deterioration, and maintains or improves the functional condition of the system without increasing structural capacity. The following are examples of PM projects: shoulder repair, including mitigation of edge drop offs, upgrading guardrail, and/or barrier components the addition of paved or stabilization of unpaved shoulders installation of milled rumble strips activities related to asphalt pavement surface preservation (e.g. crack sealing, joint sealing, slurry seal, isolated deep patching etc.) asphalt resurfacing that includes replacement of the surface lift of dense-grade asphalt, or an open-graded friction course (if present) not to exceed three inches. activities related to treatments for Portland Cement Concrete (PCC) pavements (e.g. joint sealing, grinding, dowel retrofit and partial depth repair) PCC slab replacement that does not exceed more than 50% of slabs. restoration or extension of drainage systems installation or replacement of signs and or pavement markings. GDOT Design Policy Manual ver. 2.0 Revised 5/21/2007 Other Project Types 11-1 removal of vegetation in clear zone addition and/or replacement of landscaping execution of encroachment permits activities relating to bridge preservation (e.g. crack sealing, joint repair, scour countermeasures and painting.) removal or shielding of roadside obstacles Guidelines and procedures for PM projects shall be governed by the terms of GDOT's FHWAapproved preventive maintenance agreement. 3R projects are generally defined as any pavement treatment that is neither PM nor reconstruction. The following are examples of 3R projects: resurfacing, restoration or rehabilitation activities related to structural asphalt pavement , including isolated base repair mill and inlay deeper than the first dense course, but not including the base course activities related to PCC pavement treatments (e.g. continuous slab replacement project that exceed more than 50 percent of the slabs being replaced in any given lane or area) widening of lanes and shoulders that does not increase the number of lanes selected alterations to vertical and horizontal alignments intersection improvements passing lane projects bridge and culvert rehabilitation or widening that does not increase the number of lanes Reconstruction projects are generally more complex in project scope and carry a higher cost than PM or 3R projects. The following are examples of reconstruction projects: activities related to asphalt pavement reconstruction (e.g. the removal of the entire pavement structure through the base course except for isolated base repair associated with PM or 3R projects) activities related to PCC pavement reconstruction (e.g. slab removal and replacement that is continuous throughout the project or when a significant amount of base is being replaced) 11.1.1. Procedures and Guidelines Refer to Figure 11.1. and the following text to determine appropriate preconstruction process that should be followed for each of the different categories (PM, 3R or reconstruction projects). PM projects do not need to follow the Plan Development Process (PDP)1. However, PM projects on Interstate highways require both a concept meeting and a brief concept report. 3R projects shall follow a Streamlined PDP, which is summarized in Figure 11.1. Some exceptions are listed below. 3R projects prepared by the GDOT Office of Maintenance and/or Office of Preconstruction shall follow the PDP with the following exceptions/changes: 1 GDOT. Plan Development Process (PDP). Available on the GDOT R.O.A.D.S. website at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-d-s/Other%20Resources/index.shtml GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-2 Chapter 4. Project Planning and Programming o Generally, most of this chapter will not apply to 3R projects that are using only lumpsum maintenance funds. However, in all cases, TPro2 shall be updated, as prescribed by Chapter 10 of the PDP. Figure 11.1. PDP Process for PM, 3R, and Reconstruction Projects Chapter 5. Concept Stage o 3R projects will not require an initial concept meeting o To ensure early coordination from other GDOT offices, a concept meeting, report, and solicitation of comments on the report is required. However, some of the PDP's specific requirements for a concept meeting and report may not apply if there are no right-of-way, utility, or environmental impacts o For 3R projects being developed by the GDOT Office of Maintenance, the Assistant Preconstruction Director will be responsible for distributing the concept report for comments, consolidating comments, recommending approval of the concept report, and forwarding the concept report to the Chief Engineer for approval. Chapter 6. Preliminary Design (If applicable) o A Project Design Data Book is not required 2 Refer to the GDOT PDP for additional information about TPro, the GDOT Preconstruction Project Management System. GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-3 o The preliminary and final field plan reviews may be combined if recommended by Engineering Services Chapter 7. Final Design o If no right-of-way is required, neither the Location and Design Report nor the advertising of location approval is required. Chapter 8. Design Guideline Variances o As intended by the PDP, future projects in the Statewide Transportation Improvement Plan, (STIP) and Regional Transportation Plan (RTP) will be considered in the review and approval of design exception requests. Reconstruction Projects shall follow the Plan Development Process The geometric and safety guidelines for PM, 3R, and reconstruction projects are summarized in Table 11.1. Table 11.1. Geometric and Safety Guidelines for 3R, PM, and Reconstruction Projects Classification Type of Work National Highway System (NHS) Reconstruction and 3R Interstate PM Freeway NonInterstate Reconstruction and 3R PM Reconstruction Design Standards Upgrade Guardrail if not meeting: Update Cross Slope and SE AASHTO Green Book / Interstate Stds. n/a AASHTO Green Book n/a AASHTO Green Book NCHRP 350 NCHRP 350 NCHRP 350 NCHRP 350 NCHRP 350 Yes If crash history warrants Yes If crash history warrants Yes Design Exception Approval FHWA n/a GDOT n/a GDOT Non-Freeway 3R GDOT 3R Standards (1) NCHRP 230 Yes GDOT Non-NHS PM Reconstruction n/a NCHRP 230 (2) Not required n/a AASHTO Green Book NCHRP 350 Yes GDOT Non-NHS All Roads 3R PM State Route GDOT 3R Standards (1) n/a NCHRP 230 NCHRP 230 Yes Not required PM LARP Work n/a Not Required Not required Notes: (1) Per AASHTO Green Book, as amended by this Manual, Section 11.1.2. and Section 11.1.3. (2) Upgrade existing guardrail and end terminals, if not meeting referenced standards Source: Transportation Research Board (TRB), National Cooperative Highway Research Program. GDOT n/a n/a GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-4 11.1.2. Controlling Criteria for Non-Interstate Systems (GDOT 3R Standards) Guidelines for non-interstate 3R projects will follow the current edition of the American Association of State Highway and Transportation Officials (AASHTO) A Policy on Geometric Design of Highways and Streets (Green Book) for all projects except the controlling criteria listed below will apply. Design Speed The design speed shall be equal to or greater than the posted speed. If the existing roadway does not meet the design speed criteria and cannot be reasonably corrected, a design exception must be requested and approved. For projects on roadways with no posted speed limit, an appropriate design speed should be selected by the designer. For information on selection of design speed, refer to Chapter 3. Design Controls, Section 3.2. Design Speed of this Manual. Lane Width Lane widths shall be 12-ft., except where it has been determined that a lesser width is appropriate for a given situation. For lane widths less than 12-ft., a design exception/variance must be requested. Usable Shoulder Width The usable shoulder widths for two-lane roadways is determined by classification and Average Daily Traffic (ADT). Refer to Table 11.2. Table 11.2 Usable Shoulder Width for Two Lane Roadways Roadway ADT Classification < 400 ADT 400 1,500 ADT 1,5002,000 ADT > 2,000 or DHV > 200 Local Road 2-ft. 5-ft. 6-ft. 8-ft. Multi-Lane Roadways All multi-lane roadways should have at least an 8-ft. usable shoulder. Collector Arterial 2-ft. 5-ft. 6-ft. 8-ft. 4-ft. 6-ft. 6-ft. 8-ft. Bridge Widths Geometric design standards shall be in accordance with the AASHTO Green Book. Summaries of minimum bridge widths for 2-lane and multilane bridges on non-interstate highways having state route numbers are provided in Table 11.3. and Table 11.4., respectively. Table 11.3 Minimum Bridge Widths for Non-interstate Highways Rural Sections (2-Lanes) Design Speed < 50 mph > 50 mph All Speeds All Speeds All Speeds Design Year ADT 0-399 0-399 400-1,999 (DHV < 200) 2,000 4,000 (DHV = 200-400) > 4,000 (DHV > 400) Bridge Width Clear Distance 30-ft. 32-ft. 38-ft. 40-ft. 40-ft. Design Live Loading HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18) GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-5 Table 11.4. Minimum Bridge Widths for Non-interstate Highways Multilane Rural Sections Divided/Undivided Undivided (4 or more lanes) Divided Bridge Width Clear Distance Pavement Width + 20-ft. Pavement Width + 14-ft. Minimum Shoulder Width 10-ft. right and left 4-ft. inside 10-ft. outside Minimum bridge widths for local roads and streets not having state route numbers are described below and in Table 11.5.: Table 11.5. Minimum Bridge Widths for Local Roads and Streets (Rural Sections) (1) Design Speed All Speeds Design Year ADT 0-399(2) Bridge Width Clear Distance 28-ft. Design Live Loading HS-20 (MS-18) All Speeds 400 999 30-ft. HS-20 (MS-18) All Speeds < 50 mph > 50 mph All Speeds 1,000 1,999 (DHV = 100 199) 2,000 4,000 (DHV = 200 400) 2,000 4000 (DHV = 200 400) > 4,000 (DHV > 400) 32-ft. 38-ft. 40-ft. 40-ft. HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18) HS-20 (MS-18) Notes: (1)Two lanes without curb. For low volume roads with an approach roadway width of one lane, a minimum bridge width equal to the approach roadway width may be selected with concurrence of the Chief Engineer. (2)For low volume roads with an approach pavement width of 20-ft., a bridge width of 24-ft. is permissible. In urban sections (with curb), the minimum clear width for all new or reconstructed bridges shall be the curb-to-curb width of the approaches, with the exception of 2-lane, 2-way bridges, where the minimum clear width shall be 28-ft. Sidewalks shall be provided on bridges where curb and gutter is provided on the approach roadway. The replacement of existing concrete post and open railing systems constructed prior to 1964 shall be evaluated on a case by case basis. GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-6 Table 11.6. Horizontal Clearance Structural Capacity The structural capacity for existing / retained bridges shall be: HS-15 (MS-13.5). The structural capacity for new bridges shall be: HS-20 (MS-18). Refer to the current GDOT Bridge and Structures Policy Manual3 for further guidance related to structural capacity. Horizontal Clearance The minimum horizontal clearances by posted speed are listed in Table 11.6. Note: The clearances listed are based on 1996 AASHTO Roadside Design Guide using a 50% lateral to extend probability. For curbed areas, horizontal clearance width shall be 18-inches from face of curb. Posted Speed Horizontal Clearance 35 mph 4-ft. 40 mph 4-ft. 45 mph 5-ft. 50 mph 6-ft. 55 mph 7-ft. 60 mph 8-ft. 65 mph 9-ft. Source: AASHTO. Roadside Design Guide, 1996 Vertical Clearance A minimum of 14.5-ft. shall be maintained as vertical clearance at all existing structures. Resurfacing shall be performed so as not to violate this requirement. Horizontal Alignment In cases where AASHTO guidelines are not met, refer to the conditions and corresponding policies listed in Table 11.7. Table 11.7. Horizontal Alignment for Existing Features not meeting 3R Guidelines Condition Accident History Policy < 10 mph below AASHTO guidelines Low, compared with statewide average Retain. The designer shall address and justify existing features to be retained which do not meet 3R guidelines. < 10 mph below AASHTO guidelines Directly related accident history compared with statewide average Correct to AASHTO guidelines or to the highest design speed practicable and request a design exception. > 10 mph below AASHTO guidelines Not applicable Correct to AASHTO guidelines if practicable. If not, correct to highest design practicable and request a design exception Vertical Alignment The same policies described in Table 11.7. for horizontal alignment shall apply to vertical alignment. Cross Slope Pavement cross slope shall be a minimum of 1.5% and desirable 2.0%. Cross slope should be increased to 2.5% in areas where an increase is practicable and justified. For wide pavements, cross slope can be increased with each additional lane width. 3 GDOT. Bridge and Structures Policy Manual. The current manual is available online at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-d-s/DesignPolicies/ GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-7 Grades In areas where accident history indicates a grade-related problem the designer shall correct to AASHTO guidelines; otherwise a request for a design exception will be necessary. In areas with no grade-related problems, existing grades may be retained. Superelevation Rural Collectors and Arterials: The maximum superelevation for rural collectors and arterials shall be 10%. Urban Collectors and Arterials: The maximum superelevation for urban collectors and arterials shall be 4% to 6% 11.1.3. Other Design Considerations for 3R Projects (GDOT 3R Standards) Design Speed on Roadways with no Posted Speed Limit If a roadway is paved and does not have a posted speed limit, the designer should select a design speed commensurate with the functional classification and existing geometric features of the roadway, provided such features are not defective. The selected design speed should be consistent with the speeds that drivers are traveling and are likely to expect on the facility. For county roads or city streets, the designer should coordinate with the local jurisdictional authority on the selection of the posted speed limit and the recommended design speed. Efforts should be made to have the local jurisdictional authority post a speed limit on the road equal to or less than the selected design speed. The designer should select a design speed as high as practical to attain a desired degree of safety, mobility, and efficiency within the constraints of environmental quality, economics, aesthetics, and other social or political effects. On unpaved country roads or city streets, the selected design speed shall be 35 mph or greater. A design exception will be required where this is not practical or appropriate. Shoulder Treatment and Procedures for Passing Lane, Turning Lane, or Lane Addition Projects GDOT's policies on the required widths of existing shoulders are as follows: On the widened side: Existing shoulders shall be widened to meet AASHTO Guidelines. Clear zone requirement for the specific design situation should be followed. Refer to Chapter 5, Roadside Safety and Horizontal Clearance and the AASHTO Roadside Design Guide for further guidance on clear zone requirements. On the non-widened side: Where sufficient right of way exists, shoulder widths should meet AASHTO guidelines. Where sufficient right of way does not exist and the accident data does not indicate that the existing shoulder contributes directly to the accident history, the existing shoulder may be retained. Where sufficient right of way does not exist and the accident data indicates that the existing shoulder contributes directly to the accident history, AASHTO width shoulders shall be provided unless a design exception is requested and approved. GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-8 Guardrail and/or Barrier Guardrail and/or barrier at bridge ends within the project limits shall be upgraded to current AASHTO guidelines. The designer shall evaluate the need for guardrail and/or barrier at other locations with existing warrants and consideration should be given for correction consistent with existing warrants. The designer should also take into account accident history when considering the need for additional guardrail and/or barrier. Existing guardrail and/or barrier shall be evaluated under current warrants and if warranted, upgraded to current AASHTO guidelines. If an existing guardrail and/or barrier is not warranted, it shall be removed. Where it is determined that a guardrail and/or barrier is to be replaced or installed, the additional shoulder width defined as T in GDOT Construction Standards4 shall be obtained. In some cases, obtaining the T distance may require placing guardrail and/or barrier over a portion of the existing shoulder, which would thus reduce the usable shoulder width. If this occurs, the controlling criteria described in Section 11.1.2. of this Manual shall apply, and a design exception will be required if the minimum usable shoulder width cannot be maintained. Drainage Structures All minor drainage structures shall be extended to avoid encroachment on the minimum shoulder widths as described in Section 11.1.2. of this Manual or the prevailing existing shoulder width, if it is greater. Major drainage structures shall be evaluated on a case by case basis. Major drainage structures must be extended, where necessary, to achieve the minimum (3R) shoulder widths. Where such structures encroach on existing shoulders, but are beyond the minimum widths, the designer should consider extensions or the installation of guardrail and/or barrier. Delineation (Advance Warning Signs) Delineation can be especially effective where minimum or less than desirable geometric features are involved. Since 3R projects often involve such features, GDOT allows liberal application of delineation techniques. Bridges narrower than the approach roadway and sharp curves should be delineated using reflective delineators, chevron alignment signs, or other appropriate devices. Signs and Pavement Markings The designer shall include standard signing and pavement markings in accordance with the current Manual of Uniform Traffic Control Devices (MUTCD)5. Railroad grade crossings shall be treated in accordance with current criteria. Where active protective devices are needed, they may be installed as a separate project under the Rail-Highway Crossing Improvement Program. 4 GDOT Construction Standards are available online in English and Metric units at: http://tomcat2.dot.state.ga.us/stds_dtls/index.jsp 5 FHWA. Manual on Uniform Traffic Control Devices (MUTCD). The 2003 version of this publication is available online at: http://mutcd.fhwa.dot.gov/kno-2003r1.htm GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-9 Design Exceptions Where existing features that do not meet these guidelines are proposed to be retained or constructed, the designer shall submit requests for design exceptions to Engineering Services for approval. The request for design exceptions must identify the sub-standard features, give the justification for retention, and describe any proposed mitigation. The designer shall examine accident data with the objective of identifying causative factors that could be corrected as a part of the project. If physical correction is not feasible or cost effective, mitigation measures must be considered and resolution documented in the request for design exception. The process for submitting design exception requests is outlined in the GDOT PDP. Americans with Disabilities Act (ADA) All areas shall be in compliance with Americans with Disabilities Act (ADA) requirements6 on all projects within the project limits. There are no exceptions to ADA requirements. 11.2. Special Design Considerations for Other Project Types GDOT determines the need for projects other than the traditional roadway project. The following section discusses design guidelines that are intended to provide for a uniform design approach for these types of stand alone projects. These guidelines are not intended to replace the Plan Development Process or to be a comprehensive or detailed manual for the design of these facilities, but guidelines for designers in preparing plans for these other project types. In many cases the intent of the project is clear and the designer should strive to achieve the purpose and design intent of the project within the context of earlier chapters of this Manual. Each topic contains the GDOT resource office with the most experience with a type of non-traditional, stand alone project to contact for additional information. Guidelines for the following types of projects are included in this section: bridge fencing projects; bridge jacking projects; ITS projects; signing and marking projects; and noise abatement projects. 11.2.1. Bridge Fencing Projects The resource office for bridge fencing projects is the GDOT Office of Bridge Design. The primary purpose of a bridge fencing project is to create a raised barrier that will deter persons from dropping or throwing objects from the bridge onto vehicles or pedestrians below the bridge. The raised barrier on bridge fencing projects is typically a fence that is added to an existing bridge. The project limits should be defined as the extent required to accommodate the bridge fencing. Standard fence details should be utilized whenever possible. 6 Visit the following FHWA web page for additional information relating to Americans with Disabilities Act (ADA) requirements http://www.fhwa.dot.gov/environment/te/te_ada.htm GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-10 11.2.2. Bridge Jacking Projects The resource office for bridge jacking projects is the GDOT Office of Bridge Design. The primary purpose of a bridge jacking project is to raise an existing bridge to correct a deficient vertical clearance or in anticipation of a change in the existing feature underneath the bridge that would cause a deficient vertical clearance. Roadway approaches to the existing bridge should be designed to account for the elevation difference from raising the bridge. The project limits should be defined as the extent required to accommodate the bridge jacking. Upgrading major roadway items within the project limits to current standards is not required. In addition, bridge widths and shoulders that do not meet current standards are not required to be upgraded with the bridge jacking project. Minor design elements within the project limits of the bridge jacking project should be upgraded to current standards. Minor roadway elements include such items as: guardrail, signing and marking, etc. Major design deficiencies within the project limits and minor design deficiencies outside the project limits should be noted and reported to the GDOT Office of Planning, which may then consider adding a future project to the current GDOT construction work plan. Bridge deficiencies noted in the field should be reported to the GDOT Office of Maintenance immediately. 11.2.3. Intelligent Transportation System (ITS) Projects The resource offices for ITS Projects are the GDOT Office of Traffic Operations (concept) and the GDOT Office of Traffic Safety and Design (design). The primary purpose of an ITS project is for congestion mitigation or traffic management. ITS projects include the design of systems of real-time traffic conditions sensors, surveillance devices, traffic control devices, and motorist information devices. These systems may be designed for installation along an existing roadway corridor as a stand alone project, or for inclusion into a project for other improvements to a roadway corridor. The installation of ITS devices shall not interfere with or affect the visibility of the existing signing or sight distance. Where conflicts are unavoidable, the ITS plans will include replacement signing meeting the standards and guidelines in the MUTCD and meeting GDOT standard installation details. 11.2.4. Signing & Marking Projects The resource office for signing and marking projects is the GDOT Office of Traffic Safety and Design. The primary purpose of a signing and marking project is to provide stand alone signing and marking improvements. For interstate facilities, FHWA requires all interstate safety features be upgraded to current standards within the project limits. For non-interstate projects, generally other items that do not meet current standards will not be addressed on these projects. GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-11 11.2.5. Traffic Signal Projects The resource office for Traffic Signal Projects is the GDOT Office of Traffic Safety and Design. The primary purpose of a Traffic Signal Project is to provide a traffic signal design for at-grade intersections. The majority of projects will be for the replacement and upgrade of obsolete equipment at intersections with existing signals, but this type of project may also be for the design of a new traffic signal. Geometric improvements such as turn lanes are often included in traffic signal projects, but only to the extent to provide the efficient operation of the signal. Substandard radius returns on the side streets and storage/taper lengths shall be improved wherever feasible. Raised concrete islands should be considered during design to facilitate pedestrian movements as necessary. For skewed angle intersections, turning-radius templates for an appropriate design vehicle shall be used to determine the appropriate opening. The width of the side street shall also be considered in determining the length of the median opening. 11.2.6. Noise Abatement Projects The resource office for noise abatement projects is the GDOT Office of Environmental Services (OES). Refer to Policy and Procedure 4415-11, Highway Noise Abatement Policy for Federal Aid Projects for further guidance relating to noise abatement. 11.3. Design Elements for Other Project Types 11.3.1. Survey Requirements Typically field surveys shall be considerably more limited with these other projects. Prior to commencing field surveys, the design team shall hold a pre-survey meeting and/or an onsite inspection to determine surveying requirements. Maximum use shall be made of "as-built" construction plans in order to minimize the requirements for collection of field data. As-built drawings, however, shall be verified before relying on them for accurate representation of existing conditions. Limits of surveys should be determined on a case by case basis prior to the start of surveys. The limits of surveys will depend upon the type of project. Bridge Fencing Projects For bridge fencing projects, survey sketches of each site are typically adequate as a database. The designer or design team member can perform the bridge sketches, noting the number of lanes, width of sidewalk, length and type of guardrail, etc. Each bridge should be treated as a stand-alone location, with no relationship to other bridges in the project corridor, except where bridges are close enough together to affect the design. Projectlength horizontal or vertical survey controls are not necessary. GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-12 Bridge Jacking Projects Designers should communicate with the District office and verify there is not another project planned for each bridge jacking location to determine if the bridge jacking should be included in that project and not as a separate project. Bridge Jacking Project limits will depend upon the amount of bridge raising and the impact to each roadway approach anticipated and the topography of the side slopes. Field surveys should generally include, but not be limited to: existing bridge features geometry digital terrain model (DTM) existing right-of-way (in the absence of right of way plans or visible markers, the designer may assume that the fence is the right-of-way line.) drainage structures within the project limits (curb & gutter, catch basins, manholes, median drop inlets, cross culverts, side drain pipes etc.) existing guardrail driveway locations utility poles and strain poles signage other significant topographic features ITS Projects When an ITS project is included in other roadway improvement activities, the field survey detail will be determined by the requirements of the roadway work. However, it will be necessary for the designer to obtain detailed field information at the location of the support structures required for dynamic message signs (DMS), camera support poles and other field devices such as junction boxes. Detailed topographic diagram information that includes the location of existing signs, guardrail and drainage structures is essential. Project-length horizontal or vertical survey controls are generally not necessary. Limits of surveys will be determined by the scope of the project or by the project design where the ITS devices are a supplement to other work proposed. Signing and Pavement Marking projects and Traffic Signal projects Project-length horizontal or vertical survey controls are not necessary, except in areas where sign/signal sight distance is an issue. Necessary control should be determined at a pre-survey site visit. The limits of surveys will depend upon the length of project and the topography of the roadway. Field surveys should generally include but not be limited to: existing geometry of the roadway existing right-of-way (in the absence of right of way plans or visible markers, the designer may assume that the fence is the right-of-way line.) drainage structures within the project limits (curb & gutter, catch basins, manholes, median drop inlets, cross culverts, side drain pipes etc.) existing guardrail driveway locations GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-13 utility poles and strain poles signage bridges other significant topographic features The design database shall include a schematic diagram of each roadway's geometry and significant features instead of the highly detailed mapping normally required for roadway project design. Cross sections are not required for either signing and marking projects or traffic signal projects. However, if additional safety features are to be upgraded with the project, the project manager and designer should determine whether cross sections are warranted to accomplish the design. If required, ground slopes outside existing roadways shall be provided at 50-ft. to 100-ft. intervals, as deemed appropriate by terrain conditions. Cross sections shall only be provided at areas requiring significant excavation or embankment, and may be substituted with "original plan" or "as-built" templates as long as accurate earthwork estimates can be determined. The designer shall use the ground survey data or template information to estimate earthwork quantities and to determine construction limits. In most cases, cross sections will not be required for medians, unless conditions warrant (e.g., split profile, drainage structures that may require adjustment or unusual circumstances). Noise Abatement Projects For noise abatement projects, necessary control should be determined at a pre-survey site visit. The limits of surveys and cross sections will depend upon the length of project, the topography of the roadway and ground slopes between the right of way and limits of roadway. 11.3.2. Construction Plans Unless noted otherwise, all of these other projects will be developed through the streamlined PDP or similar process. The respective resource office, in consultation with Engineering Services and the project manager, will determine the appropriate process. 11.3.3. Pavement Design Where required, it is anticipated that most pavement designs will consist of milling, overlay and leveling. Pavement designs will be provided and/or approved by the GDOT Office of Materials and Research upon completion of the existing pavement analysis and soil survey. 11.3.4. Environmental It is expected that most sites will involve a NEPA Categorical Exclusion (CE). The GDOT Office of Environment and Location shall be notified as soon as possible of any anticipated impacts to existing waterways, including streams and wetlands. 11.3.5. Earthwork If earthwork is required, normal standards shall apply; however, because earthwork is generally minimal, the earthwork shall be let as "Grading Complete - Lump Sum." The designer should calculate earthwork volumes, but no quantities shall be shown in the plans. Removal of vegetation within the clear zone shall be included within the project limits. GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-14 11.3.6. Drainage If drainage is required, normal standards shall apply. Existing drainage structures in conflict with the proposed improvements should be extended or relocated in order to maintain adequate drainage. Existing drainage patterns shall not be altered significantly without justification. 11.3.7. Guardrail and/or Barrier At locations with existing guardrail to be retained, the designer shall determine if the guardrail meets current GDOT standards discussed in earlier chapters of this Manual. All guardrail and/or guardrail anchorages within the project limits that do not meet current GDOT standards will be replaced. In locations where the guardrail extends outside the project limits, the designer shall determine if the new guardrail should tie into the existing guardrail or whether the entire run of existing guardrail should be replaced and the project limits extended. 11.3.8. Erosion Control Plans Where required, erosion control items shall be shown clearly on the construction plan sheets. Typically these other projects do not require separate Comprehensive Monitoring and Erosion Control Plans unless any one site within the project involves land disturbance of more than one acre. 11.3.9. Traffic Signal Plans The designer shall notify the GDOT Office of Traffic Operations of any anticipated impacts to existing traffic signals. 11.3.10. Signing & Markings All signs located within the project limits shall be removed and replaced unless otherwise directed. The plans should note that all signs and pavement markings shall be in accordance with MUTCD and GDOT standards. In event that MUTCD requirements or guidelines conflict with GDOT policy, GDOT policy shall take precedence. For bicycle lanes and bicycle shoulders, signs and pavement marking shall be replaced in kind. 11.3.11. Utilities The designer shall coordinate with the GDOT Office of Utilities and the District Office Utilities Engineer regarding the location of utilities. Base plan sheets shall be submitted at the earliest possible time in order to facilitate obtaining existing utilities information from utilities owners. It is anticipated that no significant public utilities relocations or adjustments will be required. 11.3.12. Traffic Control Plans In most cases, traffic control plans are not required. Standard details for traffic control should be utilized. GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-15 Chapter 11 Index Americans with Disabilities Act (ADA), 10 Bridges Fencing Projects. See Other Project Types, Bridge Fencing Jacking Projects. See Other Project Types, Bridge Jacking Design Database, 1214 Guardrail Projects. See Other Project Types, Guardrail and/or Barrier Intelligent Transportation System (ITS) Design Considerations, 11 Design Database, 13 ITS. See Intelligent Transportation System (ITS) Noise Abatement Projects Design Database, 14 Other Project Types Bridge Fencing, 10 Bridge Fencing, Design Elements, 12 Bridge Jacking, 11 Bridge Jacking, Design Elements, 13 Construction Plans, 14 Drainage, 15 Earthwork, 14 Environmental, 14 Erosion Control Plans, 15 Guardrail and/or Barrier, 15 Pavement Design, 14 Signing & Markings, 15 Traffic Control Plans, 15 Traffic Signal Plans, 15 Utilities, 15 Resurfacing, Restoration, or Rehabilitation Design Guidelines (3R) Controlling Criteria, 58 Signing & Marking Projects Design Considerations, 11 Signing & Pavement Marking Projects Design Database, 13 Signing and Marking, 11 Traffic Signal Projects Design Considerations, 12 GDOT Design Policy Manual ver. 2.0 Revised 7/21/2011 Other Project Types 11-16 Chapter 13 Contents 13. TRAFFIC FORECASTING AND ANALYSIS CONCEPTS 1 13.1. Traffic Forecasting Process 1 13.1.1. Data Collection 1 13.1.2. Functional Roadway Classification 12 13.2. Freeway Traffic Analysis and Design 12 13.2.1. ITS Technology 13 13.2.2. Capacity Analysis and Level of Service 13 13.2.3. Ramps and Ramp Junctions 15 13.2.4. Traffic Management Strategies 16 13.3. Arterial Traffic Analysis and Design 18 13.3.1. Capacity Analysis and Level of Service (LOS) 19 13.3.2. Traffic Analysis Procedures 19 13.3.3. Intersection Traffic Control and Design 20 13.4. Trip Generation and Assignment for Traffic Impact Studies 24 13.4.1. Trip Generation Data 24 13.4.2. Traffic Assignment 26 Chapter 13 Index 28 Summary of Chapter 13 Revisions 29 List of Figures Figure 13.1. Directional Counts at Three-Leg Intersections 3 Figure 13.2. Example for Determining Growth Rates Using Urban Area Transportation Models 8 List of Tables Table 13.1. Urbanized Areas with Associated Counties Table 13.2. Common ITE Land Use Codes GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Chapter 13 Contents i 13. TRAFFIC FORECASTING AND ANALYSIS CONCEPTS 13.1. Traffic Forecasting Process This chapter explains the traffic forecasting process including how traffic analysis relates to roadway design. During the course of the design process, the design engineer shall request traffic data for roadway capacity analysis to ensure that the functional requirements of the roadway are met. In addition, the traffic volumes are used to determine the pavement structure of the road. For Georgia DOT projects designed in-house, traffic volumes are supplied by the GDOT Office of Environment and Location (OEL). For consultant designed projects, the traffic volumes may be provided by GDOT, if available, or by the consultant as part of the scope of services in the consultants design contract. 13.1.1. Data Collection Site Visit The traffic engineer should conduct a site visit to gather current traffic information that is not readily available from other sources. The site visit should be conducted when preparing the scope of the project or when development of the project concept begins. The Manual on Uniform Traffic Control Devices (MUTCD)1 should be followed when collecting new data. The presence and needs of children, elderly persons, disabled, transportation disadvantaged, pedestrians, and bicyclists should be included in a typical site visit. Data to be collected during the site visit generally includes the following information: number of lanes, lane usage, and presence and type of medians curves and grades (if significant enough to affect capacity or traffic operations) lane, median, and shoulder widths traffic control devices traffic signal phasing traffic signs (particularly regulatory signs and posted speed limits) regulatory pavement markings pavement conditions sidewalks, bicycle lanes, and multi-use paths marked and unmarked crosswalk locations presence and type of on-street parking and parking regulations street lighting driveways for major vehicle generators or truck generators (collect the same information as would be collected for side streets) transit stop locations and amenities, transit schedules, and types of transit vehicles in service 1 FHWA. Manual on Uniform Traffic Control Device (MUTCD). The 2003 version of this publication is available online at: http://mutcd.fhwa.dot.gov/kno-2003r1.htm GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-1 adjacent land use, density, and occupancy roadway functional classification route governmental jurisdiction travel times Other data that may be needed includes sight distances, vertical and lateral clearances, any safety hazards, utility information (such as utility poles, storm drain, and valve cover locations), and road right-of-way locations. The (Georgia) State Roadway Functional Classification Map2 and Roadway Characteristics (RC), RCInfo file3 contain speed limits, lane widths, shoulder widths, and information on many other roadway characteristics. These resources should be reviewed prior to a site visit. The designer should contact GDOT immediately if a site visit yields information that differs from that of existing GDOT data sources. Existing Traffic Data The traffic engineer should collect existing traffic data for the analysis. Before collecting existing traffic data, the traffic engineer should send a memorandum and map that summarizes the project and site visit to the GDOT Office of Traffic Operations to confirm the locations and types of counts to be collected and to request current information. Typical traffic data requests include 24-hour volume counts (summarized by hourly or 15-minute intervals) and peak-hour (or peak period) turning movement counts. The highest traffic volumes are usually during the weekday morning (7:00 a.m. 9:00 a.m.) and evening (4:00 p.m. 6:00 p.m.) peak travel periods. However, in some areas, such as near major shopping centers or recreational areas, the highest traffic volumes may be in the evenings or on weekends. The peak hours may also change over time, especially in developing areas. The time and duration of peak periods should be verified by careful review of 24-hour volume counts. The traffic engineer should contact local government or jurisdictions to determine if there are hazardous or high-accident locations within the study area. Law enforcement agencies collect this data in many communities. Traffic engineering agencies may also collect collision data. Existing traffic data should generally be no more than one year old if available Existing traffic data needed for the analysis frequently include the following information: peak period turning movement counts (including cars, single-unit trucks and buses, and multi-unit or combination trucks) one-day directional volumes, speed; and, in some locations, vehicle classification machine counts (7-day counts in recreational areas) historic daily volume counts for the most recent fifteen years that are available (contact the GDOT Office of Transportation Data) 2 GDOT. Functional Classification Map. 2006 Available through the GDOT Office of Transportation Data website at: http://www.dot.state.ga.us/dot/planprog/transportation_data/function_class_maps/index.shtml 3 RCInfo files are generated through the GDOT Network. Access to the network can be obtained through the GDOT Division of Information Technology. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-2 accident history for the most current three years at locations identified by the local jurisdiction (contact the GDOT Office of Traffic Operations) Bicycle and pedestrian counts should not be requested as part of the traffic study unless the project is located where there are high concentrations of pedestrians and bicyclists, such as at a university campus, event center or a central business district. Daily machine traffic counts should be adjusted by seasonal and axle factors to estimate existing AADT volumes. The GDOT Office of Transportation Data can furnish factors from previous years, but data from nearby count locations should be used to determine the seasonal factors. Nearby tube counts can be used to determine vehicle classification and thus the axle factor. Any adjustments to raw traffic counts should be discussed and mutually agreed upon between the traffic engineer and the person responsible for review and approval. Establish Existing Traffic Patterns Directional roadway volumes and turning movements for a.m. peak hour and p.m. peak hour at the study intersections need to be established. The traffic engineer can accomplish this by collecting new counts where data is needed. Since counting all traffic data locations may not always be practical, GDOT has established the a procedure for estimating the existing turning movement counts from directional counts at three-leg intersections, as illustrated in Figure 13.1. A, B, and C are the approach volumes on each leg. X = (A + B + C) / 2 Where: X - C = A to B and B to A X - B = A to C and C to A X - A = B to C and C to B Source: TRB. Highway Capacity Manual. 2003 Figure 13.1. Directional Counts at Three-Leg Intersections For four-leg intersections, the traffic engineer should first make assumptions about the traffic on the minor leg, then follow the three-leg procedure for the other three legs. Furthermore, GDOT assumes that at the intersection of two major routes, 55% to 70% of the trips on each approach are going straight. Daily Volumes and Their Uses Traffic volume data is commonly reported as a daily value. Daily volumes are typically used for highway planning, as is general observations of volume trends and the design of pavement structures. The following four daily volumes are typical or widely used: Average Annual Daily Traffic (AADT) is defined as the average 24-hour traffic volume at a given location over a full, 365-day year. This means the total of vehicles passing the site in a year divided by 365. The GDOT Office of Transportation Data maintains Georgias State GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-3 Traffic and Report Statistics (STARS) web site (http://www.dot.state.ga.us/dot/planprog/transportation_data/TrafficCD/index.shtml), which provides AADT counts collected from permanent and portable traffic collection devices throughout the state during the years 1999-2005 for every segment of Georgia's State Highway System. Average Daily Traffic (ADT) is defined as the average 24-hour traffic volume at a given location for some period of time less than a year. While AADT is a full year, an ADT may be measured for six months, a season, a month, and a week or as little as two days. Therefore, an ADT is valid only for the period for which it was measured. Average Annual Weekday Traffic (AAWT) is defined as the average 24-hour traffic volume occurring on weekdays over a full year. This volume is of considerable interest when weekend traffic is light, so that averaging 24-hour volumes over 365 days would mask the impact of weekday traffic. AAWT is computed by dividing the total weekday traffic for the year by 260. Average Weekday Traffic (AWT) is defined as the average 24-hour traffic volume occurring on weekdays for some period of time less than one year. The unit by which all of these volumes are measured is vehicles per day (vpd). Daily volumes are typically not differentiated by direction or lane, but are the totals for the entire facility at a given location. Base Year and Design Year Traffic For all GDOT projects, the design engineer should request traffic volumes for the base year and design year. The base or opening year is the year the project is anticipated to be open for traffic use. The designer should not confuse this year with the construction programmed date or the project let (bid award) date. For example, if a project is scheduled for a let date sometime in 2006 and it is estimated that the project will take two years to construct, then the volumes for the base year 2008 should be requested. The design year is the anticipated future life of the project. For all GDOT projects, the future traffic volumes will be 20 years from the base year. For example, the design engineer would request 2028 design year traffic volumes for the base year 2008. For some projects the design year may be shorter than 20 years (i.e., two years or five years) such as for minor safety and intersection improvement projects or interim projects that may be programmed to address a short-term operational problem at a location along the roadway. The design engineer is advised to confirm the base and design years early in the concept development stage of the project. The base year ADT for an existing roadway should be calculated from real traffic counts and adjusted to reflect appropriate axle factors and seasonal factors. For accuracy, the axle factors should be obtained from a vehicle classification count conducted at the same time as the traffic counts. Many count machines can collect both types of data simultaneously. Truck percentages and seasonal adjustment factors can also be found in the GDOT RC database available from the Office of Transportation Data. Base year and design year ADTs should be determined for each link of the roadway between major intersections and for each side street. Design year traffic volumes can be developed by use of either an Urban Area Transportation Model or historical traffic growth trends. The historical growth calculations are also useful for checking the reasonableness of projections from the urban traffic model. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-4 Urban Area Transportation Models Georgia presently includes fifteen different Metropolitan Planning Organizations (MPOs) with a population of more than 50,000 people. The fifteen areas range from an area of one county to several counties. GDOT develops a long-range traffic forecasting model for each MPO, except for Atlanta and Chattanooga. GDOT updates each model every five years. The fifteen Georgia MPOs are presented in Table 13.1. The forecasting model is a transportation tool for determining long range traffic volumes on the functionally classified road network (collector roads and above). There are eight recommended model networks that may be developed for each of the different MPOs. These models may not include all of the counties within the urbanized area, since MPOs are required to only include 75% of the urbanized areas. The counties that are in the long range transportation models are determined by the MPOs. The MPOs are responsible for collecting the social and economic data for the base year model and future year model. The social and economic data includes population, employment, school enrollment, growth trends, and other demographic information. The MPOs are also responsible for disseminating information from the models to the public. The eight recommended models developed by GDOT are described below. Networks 2 through 7 build upon and address deficiencies of lower numbered networks. Table 13.1. Urbanized Areas with Associated Counties Urbanized Area Albany Athens Atlanta Augusta Brunswick Chattanooga Columbus Dalton County Dougherty Lee Clarke Oconee Madison Barrow Bartow Cherokee Clayton Cobb Coweta DeKalb Douglas Fayette Forsyth Fulton Gwinnett Henry Newton Paulding Rockdale Spalding Walton Columbia Richmond Aiken Edgefield Glynn Catoosa Walker Hamilton Muscogee Lee Russell Whitfield State Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia South Carolina South Carolina Georgia Georgia Georgia Tennessee Georgia Alabama Alabama Georgia Base Year (Network 1) - This network Gainesville should include all functionally-classified roads in the study area open to traffic in the Hinesville base year (for example, 2003 base year). Macon Functional classification is based on GDOTs RCInfo file. Functionally-classified roads Rome include all roadways not coded as urban Savannah local = 19 or rural local = 9. Local roadways may appear in the base year network but are Valdosta not required to be there. Once this network is calibrated, it should replicate the travel Warner Robins patterns that existed in the base year. The base year may not be the same as the projects base year. Hall Liberty Long Bibb Jones Floyd Chatham Lanier Lowndes Berrien Houston Peach Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Georgia Do-Nothing System Projects (Network 2) - This network is intended to show what would happen in the plan year 2030 model if no new projects were built. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-5 Network 2 basically reflects "now" roadways with resulting capacity deficiencies from future traffic conditions. Network 2 consists of the base year network plus any projects under construction, opened to traffic since the base year, or projects for which funds have been authorized but construction has not yet begun. Network 2 examples include: projects under construction in the base year; projects opened to traffic since the base year; projects authorized for construction at the time of preparing this network. Existing + Committed (E+C) System Projects (Network 3) - This network is intended to show what would happen in the future if only existing and presently committed projects were built. Network 3 basically reflects "committed" short range improvements. Committed projects are defined as those projects in the current State Transportation Implementation Plan/Transportation Improvement Program (STIP/TIP) having either right-of-way (ROW) or Construction dollars shown. Projects with only preliminary engineering (PE) monies in the STIP/TIP are not considered "committed" when building such a model system. No long range plan projects would appear in this Network. A Network 3 example is projects with ROW or construction in the FY05-07 STIP/TIP. Remainder of TIP, PE, and TIER 2 Projects and Construction Work Program (CWP4) Projects (Network 4) - Network 4 basically reflects previously programmed mid-range improvements. Network 4 includes programmed projects from TIER 25, the second phase of the TIP document (last three years). Programmed projects in TIER 2 should coincide with the last three years of the CWP. Projects with PE monies would be included in this network. MPOs sometimes place "desired" projects in the TIER 2 section of the TIP document without an identified dedicated funding source. If a project has not been programmed (does not have a GDOT Project Locator number) or does not have locally dedicated funds allocated, it should not be included in this network. A Network 4 example is projects with any phase programmed for FY08-10 in the FY05-2010 TIP/TIER2/CWP. Remainder of Programmed LRTP Projects (Network 5) - Network 5 basically reflects programmed long range projects from the current LRTP. This network includes current Long Range Transportation Plan (LRTP) projects that are programmed by GDOT as long range. Current LRTP projects not yet programmed are not to be included in Network 5. If local jurisdictions have a method of documenting programmed local projects already included in the current LRTP, those projects could be included in this network. A Network 5 example is projects with PE, ROW or construction programmed by GDOT for LR = beyond the CWPs last year of 2010. NOTE: If time for completing the traffic forecasting is limited, Networks 5 and 6 may be combined. Remainder of LRTP Projects (Network 6) - This network includes projects in the current LRTP that have not been captured in any of the previous networks. A Network 6 example is projects listed in the current LRTP that have not advanced from their status as LRTP "recommendations". 4 The CWP is a GDOT document listing state and federally funded projects approved by the Transportation Board for preliminary engineering, ROW acquisition, and/or construction scheduled in the current and next five fiscal years (total six years), e.g., FY05-10 CWP. 5 TIER 2 refers to the last three years of projects typically included in the MPOs TIP document, but not considered part of the official TIP recognized by FHWA, e.g., FY05-07 TIP; FY08-10 TIER 2. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-6 New Projects Recommended Plan for Public Comment (Network 7) - This network includes any new project that does not appear in the current LRTP, including LR projects programmed by GDOT but not included in the current LRTP. This network provides the opportunity to test various improvement scenarios and could actually consist of several networks, possibly deleting projects included in previous networks. This series of analyses could produce two networks for public comment: (1) an aspirations plan, and (2) the financially constrained recommended plan. The latter plan is required to receive public review and comment. Recommended Financially Constrained Plan6 Post Public Comment (Network 8) This network may or may not be needed. Upon reviewing and responding to public comments received on the draft LRTP, the MPOs staff or committees may request Network revisions or additional scenarios. If significant changes are made, for example new projects not previously presented to the public, additional public comment may be needed. If the public had the opportunity to comment on the projects proposed for revision, additional public comment may not be needed. These decisions are for the MPO staff or are handled through the committee process. Whatever action is decided must be consistent with the MPOs adopted public involvement process (PIP). The final network must be consistent with the financially constrained LRTP adopted by the Policy Committee. Traffic Projections from the Urban Area Transportation Model For a roadway improvement project on an existing roadway, the traffic engineer should use the E+C model to determine the routes estimated traffic volumes. For a roadway improvement project on a new roadway, or a roadway not included in the E+C model, the volumes from the first model where it is included should be used. To determine design year traffic for a project using an urban area transportation model, the volumes can be prorated or extrapolated based on the growth in traffic between the base model year and the year of the E+C Model. However, if there is a discrepancy between the existing model and existing counts, it is better to determine that difference and add this to the existing traffic. A more general approach for using the model would be to obtain an average percent growth of all the roads in the project area from the travel demand model between the base year and the future year and apply this percent growth to the proposed roadway improvement. In most cases, volumes from the model should not be used as design traffic. The model traffic can be used to determine the absolute growth (i.e. future volume minus base year volume) for each modeled roadway, then that absolute growth can be added to the traffic count for the roadway segment. This method removes any error that was present in the base year model. An example of this is shown in Figure 13.2. Socio-economic data is also available within the model, including a population, number of households, employment, and school enrollment for each Traffic Analysis Zone (TAZ). 6 Financial Constraint: The LRTP must demonstrate that anticipated revenues meet or exceed anticipated costs for the LRTPs recommendations. This requires that the cost of all projects be summed together and that this total cost be compared to anticipated monies available. It must be shown that there are enough monies available to pay for the projects. If the lead transportation agency calculates that monies available are less than the sum of project costs, then projects must be removed. All plan projects including roads, bridges, bike/pedestrian, transit, passenger rail, and maintenance should be accounted for in the project cost estimates and the revenues available analysis to show a financially constrained plan. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-7 Figure 13.2. Example for Determining Growth Rates Using Urban Area Transportation Models GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-8 Establish Traffic Growth Rate Trends The traditional traffic forecasting method relies greatly on historical trends. Historical counts for the past fifteen years should be used if available. The counts should be smoothed to eliminate any bad counts and to show the general trend. Using the least squares method (Excel program), calculate base year and design year volumes based on the last fifteen, ten, and five years, giving the most weight to the ten year trend. This calculation is performed for each coverage count location along the project and for the cross streets. The base year volume is divided by the existing year volume to get the base year factor, and the design year volume is divided by the base year volume to get the design year growth factor. Historical trend analysis is only part of the traffic forecasting process. Other factors to consider are population growth data, land use plans, planned development, and anything else that might affect future traffic. This information should be available from city/county officials, planners, and other roadway designers. Trips from major real estate development or other major traffic generator should be added based on techniques described in the latest edition of the ITE Trip Generation Handbook. Using all available information, the traffic forecaster must use his/her judgment to decide the future growth rates for the project. When an existing route is paralleled by a much more attractive new route or improved facility, the total traffic on the two roads will be greater than that on the old road before the new one was opened. The additional traffic above that which can be accounted for by diversion and normal growth is defined as "generated traffic." This generated traffic is made up of the following classes of trips: 1. Trips which would not have been made at all, or made less frequently, if the improvement was not available. 2. Trips which would have been made to other destinations or from other origins. For example, shopping or business trips might be changed because of a shift in relative ease of travel. 3. Trips diverted from other forms of transportation. This mostly applies to new interstate routes. 4. Trips resulting from new developments along the road that are developed simultaneously with the construction of the new road. Generated traffic is greatest for new interstate routes and other freeways. A little generated traffic can be expected for widening projects. Judgment is used to decide how much to modify the normal growth factor. Generally the normal growth factor should be multiplied by a range of 1.00 (no adjustment) to about 1.60 (for new interstates) to account for generated traffic. Traffic Projections for New Roadway Corridors Traffic projections for a new roadway or bypass route can be determined based upon traffic counts, an origin-destination study, or from the local MPO transportation model. The percentage of traffic that will be relocated to the new route can be determined in several ways. For a minor bypass route, existing traffic counts obtained on nearby roadways will generally show a trend that can be used to determine how much of the traffic would continue along the bypass and how much traffic would be distributed to the local network of the community being bypassed. A more accurate determination of the percentage of traffic that would use a bypass route within a non- GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-9 urbanized area is to conduct an origin-destination study. Refer to the current Institute of Transportation Engineers (ITE) Manual on Uniform Transportation Engineering Studies for procedures for conducting an origin-destination study. The questions to be asked during the origindestination study interview should be included in the Traffic Data Memorandum and submitted to the Office of Environment and Location (OEL) for approval. Another method for an origindestination study is to conduct a license plate study, either manually or electronically. Within an urbanized area, the transportation model should be used to determine the amount of traffic on a new bypass route. Typically, new roadways are already included in the transportation model. Their design traffic volumes can be read directly from the loaded model network. If this is not the case, the new route should be added to the future year model to determine the design year traffic. Preliminary Traffic Projections Using traffic growth rates developed in accordance with the preceding methodology, calculate future traffic for several sections along the project and compare this with traffic projections from the urban area transportation model where available. The two projections should be within 10 percent of each other. It is important to consider whether or not the future roadway can handle the expected traffic volumes. If not, adjustments may need to be made because of limited road capacity. Adjustments to Design Year ADT Volumes For some roadway design projects, the traffic engineer may be required to adjust the volumes projected by OEL. These adjustments will be required in anticipation of major land developments or significant changes in nearby street/ highway networks that will affect future traffic volumes expected on the roadway under design. Adjustments in traffic volumes for major land developments should follow any procedures established by OEL and the impacts should be approved by OEL before the adjusted volumes are used in design by the design engineer. The design engineer should document any assumptions made and the procedures used in the adjustment of the traffic volumes. Detailed Traffic Forecast Using the established growth rates, base year and future year turning movements are calculated for each intersection along the project limits. The existing year turning movements should be used as a pattern. The traffic engineer must decide if the same pattern will hold in the future as exists now. The traffic engineer should also examine each intersection for reasonableness of the growth rate, and make adjustments as needed. For example, a built-out subdivision will have little, if any, growth, while other roads in the same general vicinity might grow at a higher rate. The traffic forecaster must use his/her judgment. Turns might need adjustment based on future land use and/or development. In most cases, the volumes in each direction should be the same. If there is a difference, the traffic engineer should provide a reasonable explanation. Design Hourly Volumes While daily volumes are very useful in planning, hourly volumes are also needed for the design process. Volumes may vary significantly during the course of a 24-hour day with periods of maximum volume occurring during the morning or afternoon rush hours. The single hour of the day that has the highest hourly volume is called the "peak hour". Capacity and other traffic analyses typically focus on the peak hour of traffic volumes, because it represents the most critical period for operations and has the highest capacity requirement. This peak-hour volume will vary from day to day or from season to season. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-10 The relationship between the hourly volume and the maximum rate of flow within an hour is defined as the peak-hour factor (PHF). For design and traffic analysis, peak volumes are usually measured for a period of time less than an hour, usually a 15-minute period. The design engineer should use the 15-minute period for all road capacity analysis. The design hour volume (DHV) is the traffic volume used to determine the number of traffic lanes on the roadway. The following formula expresses the relationship between the design hour volume and the average daily traffic volume: DHV = AADT x K where: DHV = design hour volume of traffic (total, 2-way) AADT = average 24-hour weekday, 2-way volume of traffic K = ratio of design hour volume to AADT At major intersections and at driveways leading to major activity centers, the design hour turning volumes are important in determining the intersection capacity, resulting number of lanes, and the storage length for exclusive turning lanes required for each approach. For intersections being reconstructed and that are in fully developed areas, existing turning movement percentages will be collected in the field and assumed to be the same for the future design year. For new intersections or for those significantly impacted by new land developments or major changes in nearby street/highway networks, existing and projected traffic data along with engineering judgment will be used to reassign vehicle trips on nearby street networks to derive the turning movements at project intersections. Future traffic volumes shall be used to ensure that the road has enough traffic carrying capacity. The traffic volume during a period of time shorter than a day shall be used for design purposes, reflecting peak hour periods. For roads with unusual or highly seasonal fluctuation in traffic volumes, the 30th highest hour of the design year should be used. This can be computed using seasonal adjustment factors discussed in the previous section. Locations where this technique may be necessary include beach or mountain resorts, and roadways serving major sporting arenas or performance halls. The directional design hour volume is the traffic volume for the rush hour period in the peak direction of flow. Use directional distribution factors based on existing traffic counts. If this information is not available the traffic engineer should assume that 60% of the traffic is going in one direction. For a more detailed analysis of intersection and road capacity, procedures should be used as described in the latest version of the TRB Highway Capacity Manual. Using short-term counts along the project, peak hour and directional factors can be calculated and compared to any automatic traffic recorder (ATR) locations along the route. If there are no ATR locations along the route, ATR locations along nearby routes with the same functional class can be used. Appropriate K and D factors must be discussed and approved with appropriate GDOT staff. The K and D factors are applied to the ADT derived above to calculate the a.m. and p.m. design hour volumes. Since the DHV is the 30th highest hour, the p.m. movement is usually the return movement from the a.m. movement. In some cases, separate a.m. and p.m. volumes may need to be calculated. Also, sometimes the base year peak hour volumes (PHV) are needed. They are calculated the same way using the base year ADT. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-11 Determine Truck Factors Appropriate data sources must be used to determine 24-hour and peak hour truck percentages. As described previously in this chapter, the traffic engineer must seriously consider the new traffic counts taken specifically for this purpose. The 24-hour percentage should be given as Single Unit (SU) trucks, Classes 4 through 7 and Multi-Unit or Combination (MU) trucks, Classes 8 through 15. Single Unit trucks include buses. Finalize Traffic Forecast The traffic projections and design factors are finalized and submitted as MicroStation design files to GDOT, Head of Traffic Analysis Section for approval. The submittal should meet section standards as to size of drawings and lettering. 13.1.2. Functional Roadway Classification Refer to Chapter 3. Design Controls, Section 3.1. Functional Classifications for Freeways, Arterials, Collectors and Local Roads, for a detailed discussion relating to functional roadway classification. 13.2. Freeway Traffic Analysis and Design Traffic Analysis and Design The purpose of this section is to provide some traffic analysis guidance for design engineers on some of the factors and design elements to consider in operational and road capacity analysis. This information is intended as a supplement to GDOT adopted standards and procedures outlined in the Transportation Research Board (TRB) Highway Capacity Manual. The TRB Highway Capacity Manual provides comprehensive guidelines related to freeway traffic analysis and design. Some considerations that must be made during the traffic analysis and design process include, but are not limited to: A freeway experiencing extreme traffic congestion differs greatly from a non-freeway facility experiencing extreme congestion since the travel conditions creating the congestion are internal to the facility, not external to the facility. Freeway facilities may have interactions with other freeway facilities in the area as well as other classes of nearby roads, and the performance of the freeway may be affected when travel demand exceeds road capacity on these nearby road systems. For example, if the street system can not accommodate the demand exiting the freeway, the over-saturation of the street system may result in queues backing onto the freeway, which adversely affects freeway travel. The traffic analysis and design process must also recognize that the freeway system has several interacting components, including ramps and weaving sections. The performance of each component must be evaluated separately and their interactions considered to achieve an effective overall design. For example, the presence of ramp metering affects freeway demand and must be taken into consideration in analyzing a freeway facility. High occupancy vehicle (HOV) lanes require special analysis. If an HOV facility has two or more lanes in each direction all or part of the day and if access to the HOV facility is limited from adjacent freeway lanes (i.e. 1 mile or greater access point spacing), these procedures may be used. Otherwise, HOV lane(s) will have lower lane capacities. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-12 13.2.1. ITS Technology Intelligent transportation systems (ITS) strategies aim to increase the safety and performance of roadway facilities. For freeway and other uninterrupted-flow highways, ITS may achieve some decrease in headways, which would increase the capacity of these facilities. In addition, even with no decrease in headways, level of service might improve if vehicle guidance systems offered drivers a greater level of comfort than they currently experience in conditions with close spacing between vehicles. "Many of the ITS improvements, such as incident response and driver information systems, occur at the system level. Although ITS features will benefit the overall roadway system, they will not have an impact on the methods to calculate capacity and level of service for individual roadways" (TRB, 2000 p. 2-6). 13.2.2. Capacity Analysis and Level of Service TRB defines capacity as the maximum hourly rate at which persons or vehicles reasonably can be expected to traverse a point or uniform segment of a lane or roadway during a given period under prevailing roadway, traffic, and control conditions; adding that "Capacity analysis is a set of procedures for estimating the traffic-carrying ability of facilities over a range of defined operational conditions (2000, p. 2-1)". Service flow rates are similar because they define the flow rates that be accommodated while still maintaining a given level of service. There are numerous factors that affect capacity and LOS: base conditions prevailing roadway conditions (including geometric and other elements) prevailing traffic conditions, which also account for vehicle type (e.g. heavy vehicles) and distribution of vehicles For design LOS for GDOT roadways, refer to Chapter 6, Tables 6.1 through 6.4 of this Manual. Traffic Flow Characteristics Traffic flow on a freeway can be highly varied depending on the conditions constraining flow at upstream and downstream bottleneck locations. Bottlenecks can be created by ramp merge and weaving segments, lane drops, maintenance and construction activities, accidents, and objects in the roadway. An incident does not have to block a travel lane to create a bottleneck. For example, disabled vehicles in the median or on the shoulder can influence traffic flow within the freeway lanes. Freeway research has resulted in a better understanding of the characteristics of freeway flow relative to the influence of upstream and downstream bottlenecks. Freeway traffic flow can be categorized into three flow types: (1) under-saturated, (2) queue discharge, and (3) oversaturated. Each flow type is defined within general speed-flow-density ranges, and each represents different conditions on the freeway. Under-saturated flow represents traffic flow that is unaffected by upstream or downstream conditions. This regime is generally defined within a speed range of 55 to 75 mph at low to moderate flow rates and a range of 40 to 60 mph at high flow rates. Queue discharge flow represents traffic flow that has just passed through a bottleneck and is accelerating back to the free-flow speed of the freeway. Queue discharge flow is characterized by relatively stable flow as long as the effects of another bottleneck downstream are not present. This GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-13 flow type is generally defined within a narrow range of 2,000 to 2,300 passenger cars, per hour, per lane (pcphpl), with speeds typically ranging from 35 mph up to the free-flow speed of the freeway segment. Lower speeds are typically observed immediately downstream of the bottleneck. Depending on horizontal and vertical alignments, queue discharge flow usually accelerates back to the free-flow speed of the facility within 0.5 to 1 mile downstream from the bottleneck. Studies suggest that the queue discharge flow rate from the bottleneck is lower than the maximum flows observed before breakdown. A typical value for this drop in flow rate is approximately 5 percent. Oversaturated flow represents traffic flow that is influenced by the effects of a downstream bottleneck. Traffic flow in the congested regime can vary over a broad range of flows and speeds depending on the severity of the bottleneck. Queues may extend several thousand feet upstream of the bottleneck. Freeway queues differ from queues at intersections in that they are not static or ,,standing. On freeways, vehicles move slowly through a queue, with periods of stopping and movement. Speed-Flow and Density-Flow Relationships The free-flow speed of passenger cars (mph) on freeways is relatively insensitive to flow rate of passenger cars per hour per lane (pcphpl) in the low to moderate range (0 pcphpl to 1,200 pcphpl). Studies have shown that passenger cars operating at a free-flow speed of 70 mph maintain the operating speed for flows up to 1,300 pcphpl For lower free-flow speed, the region over which speed is insensitive to flow extends to higher flow rates. In general terms, the lower the flow rate, the higher free-flow speed of the vehicle. Similarly, the higher the flow rate, the higher the density, which is measured in passenger car per mile per lane (pc/mi/ln). Refer to the current TRB Highway Capacity Manual Chapter 13, Freeway Concepts, for a detailed discussion and exhibits specific to Speed-Flow and Density-Flow Relationships and factors that affect free-flow speed. Passenger-Car Equivalents The concept of vehicle equivalents is based on freeway conditions in which the presence of heavy vehicles, including trucks, buses, and recreational vehicles, creates less than base operating conditions. These diminished operating conditions include longer and more frequent gaps of excessive length both in front of and behind heavy vehicles, the speed of vehicles in adjacent lanes, and the physical space taken up by a large vehicle (typically two to three times greater than a passenger car). To allow for these lesser travel conditions and ensure the method for freeway capacity is based on a consistent measure of flow, each heavy vehicle is converted to a passengercar equivalent. The conversion results in a single value for flow rate in terms of passenger cars per hour per lane (pcphpl). The conversion factor depends on the proportion of heavy vehicles in the traffic stream and the length as well as the severity of the roadway grade. Driver Population Studies have shown that non-commuter driver populations display different, less aggressive characteristics than regular commuters. For recreational traffic, capacities have been observed to be as much as 10 to 15 percent lower than for commuter traffic traveling on the same segment Level of Service (LOS) Although speed is a major concern of drivers as related to service quality, freedom to maneuver within the traffic stream and proximity to other vehicles are equally noticeable concerns. These qualities are related to the density of the traffic stream. Unlike speed, density increases as flow increases up to capacity, resulting in a measure of effectiveness that is sensitive to a broad range of flows. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-14 The following brief descriptions summarize the different levels of service: LOS A - Free flow, with low volumes and high speeds (about 90% of free-flow speed). Control delay at signalized intersection is minimal. LOS B - Reasonably free flow, speeds (70% of free-flow speed) beginning to be restricted by traffic conditions. Control delay at signalized intersection is not significant. LOS C - Stable flow zone, most drivers restricted in freedom to select their own speed (50% free-flow speed). LOS D - Approaching unstable flow, drivers have little freedom to maneuver (40% free-flow speed). LOS E - Unstable flow, may be short stoppages. High volumes, lower speeds (33% free-flow speed). LOS F - Forced or breakdown flow. Intersection congestion is likely at critical signalized locations with high delays and high volumes and extensive queues. Operating characteristics are represented by a specified LOS ranging from LOS A describing freeflow operations to LOS F describing breakdowns in vehicular flow. Breakdowns occur when the ratio of existing demand to actual capacity or of forecast demand to estimated capacity exceeds 1.00. Vehicular flow breakdowns occur for a number of reasons: Traffic incidents can cause a temporary reduction in the capacity of a short freeway segment, so that the number of vehicles arriving at the point is greater than the number of vehicles that can move through it. Points of recurring congestion, such as merge or weaving segments and lane drops, experience very high demand in which the number of vehicles arriving is greater than the number of vehicles discharged. In forecasting situations, the projected peak-hour (or other) flow rate can exceed the estimated capacity of the location. Freeway Weaving Weaving is defined as the crossing of two or more traffic streams traveling in the same direction along a significant length of highway without the aid of traffic control devices (with the exception of guide signs). Weaving segments are formed when a merge area is closely followed by a diverge area, or when an entrance ramp is closely followed by an exit ramp and the two are joined by an auxiliary lane. Weaving segments may exist on any type of facility: freeways, multilane highways, two-lane highways, interchange areas, urban streets, or collector-distributor roadways. Refer to the current version of the TRB Highway Capacity Manual,Chapter 24, for guidance related to freeway weaving. 13.2.3. Ramps and Ramp Junctions A ramp is a length of roadway providing an exclusive connection between two highway facilities. On freeways, all entering and exiting maneuvers take place on ramps that are designed to facilitate smooth merging of on-ramp vehicles into the freeway traffic stream and smooth diverging of offramp vehicles from the freeway traffic stream onto the ramp. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-15 Refer to the current version of the TRB Highway Capacity Manual for guidance related to ramps and ramp junctions. Capacity of Merge and Diverge Areas There is no evidence that merging or diverging maneuvers restrict the total capacity of the upstream or downstream basic freeway segments. Their influence is primarily to add or subtract demand at the ramp-freeway junction. Thus, the capacity of a downstream basic freeway segment is not influenced by turbulence in a merge area. The capacity will be the same as if the segment were a basic freeway segment. As on-ramp vehicles enter the freeway at a merge area, the total number of ramp and approaching freeway vehicles that can be accommodated is the capacity of the downstream basic freeway segment. Similarly, the capacity of an upstream basic freeway segment is not influenced by the turbulence in a diverge area. The total capacity that may be handled by the diverge junction is limited either by the capacity of the approaching (upstream) basic freeway segment or by the capacity of the downstream basic freeway segment and the ramp itself. Most breakdowns at diverge areas occur because the capacity of the exiting ramp is insufficient to handle the ramp demand flow. This results in queuing that backs up into the freeway mainline. Another capacity value that affects ramp-freeway junction operation is an effective maximum number of freeway vehicles that can enter the ramp junction influence area without causing local congestion and local queuing. For on-ramps, the total entering flow in lanes 1 and 2 of the freeway plus the on-ramp flow can not exceed 4,600 pc/h. For off-ramps, the total entering flow in Lanes 1 and 2 can not exceed 4,400 pc/h. Demands exceeding these values will cause local congestion and queuing. However, as long as demand does not exceed the capacity of the upstream or downstream freeway sections or the off-ramp, breakdown will normally not occur. Thus, this condition is not labeled as LOS F, but rather at an appropriate LOS based on density in the section. If local congestion occurs because too many vehicles try to enter the merge or diverge influence area, the capacity of the merge or diverge area is unaffected. In such cases, more vehicles move to outer lanes (if available), and the lane distribution is approximated. Levels of service in merge and diverge influence areas are defined in terms of density for all cases of stable operation, LOS A through E. LOS F exists when the demand exceeds the capacity of upstream or downstream freeway sections or the capacity of an off-ramp. Required Input Data and Estimated Values Exhibit 13-17, listed on page 13-24 of the TRB Highway Capacity Manual, provides default values for input parameters in the absence of local data (Number of Ramp Lanes, Length of Acceleration/Deceleration Lane, Ramp free-flow speed, Length of Analysis Period, PHF, Percentage of Heavy Vehicles, and Driver Population). Exhibits 13-18 and 13-19, listed on page 1325, provide direction in the determination of acceleration and deceleration lane lengths. Service volumes for ramps are difficult to describe because of the number of variables that affect operations. Exhibit 13-20, listed on page 13-26 of the TRB Highway Capacity Manual, provides approximate values (for illustrative purposes only) associated with LOS for single on- and offramps. 13.2.4. Traffic Management Strategies Freeway traffic management is the implementation of strategies to improve freeway performance, especially when the number of vehicles desiring to use a portion of the freeway at a particular time exceeds its capacity. There are two approaches to improving system operation. Supply GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-16 management strategies work on improving the efficiency and effectiveness of the existing freeway or adding additional freeway capacity. Demand management strategies work on controlling, reducing, eliminating, or changing the time of travel of vehicle trips on the freeway while providing a wider variety of mobility options to those who wish to travel. However, in actual application, some strategies may address both sides of the supply/demand equation. The important point is that there are two basic ways to improve system performance. Supply management strategies are intended to increase capacity. Capacity may be increased by building new pavement or by managing existing pavement. Supply management has been the traditional form of freeway system management for many years. Increasingly, the focus is turning to demand management as a tool to address freeway problems. Demand management programs include alternatives to reduce freeway vehicle demand by increasing the number of persons in a vehicle, diverting traffic to alternate routes, influencing the time of travel, or reducing the need to travel. Demand management programs must rely on incentives or disincentives to make these shifts in behavior attractive. Freeway traffic demand management strategies include the use of priority for high-occupancy vehicles, congestion pricing, and traveler information systems. Some alternative strategies such as ramp metering may restrict demand and possibly increase the existing capacity. In some cases, spot capacity improvements such as the addition of auxiliary lanes or minor geometric improvements may be implemented to better utilize overall freeway system capacity. Freeway Traffic Management Process Freeway traffic management is the application of strategies that are intended to reduce the traffic using the facility or increase the capacity of the facility. Person demand can be shifted in time or space, vehicle demand can be reduced by a shift in mode, or total demand can be reduced by a variety of factors. Factors affecting total demand include changes in land use and elimination of trips due to telecommuting, reduced workweek, or a decision to forgo travel. By shifts of demand in time (i.e. leaving earlier), shifts of demand in space (i.e. taking an alternative route), shifts in mode, or changes in total demand, traffic on a freeway segment can be reduced. Likewise, if freeway capacity has been reduced (i.e. as the result of a vehicle crash that has closed a lane or adverse weather conditions), improved traffic management can return the freeway to normal capacity sooner, reducing the total delay to travelers. The basic approach used to evaluate traffic management is to compare alternative strategies. The base case would be operation of the facility without any freeway traffic management. The alternative case would be operation of the facility with the freeway traffic management strategy or strategies being evaluated. The alternative case could have different demands and capacities based on the conditions being evaluated. The evaluations could also be made for existing or future traffic demands. Combinations of strategies are also possible, but some combinations may be difficult to evaluate because of limited quantifiable data. Freeway traffic management strategies are implemented to make the most effective and efficient use of the freeway system. Activities that reduce capacity include incidents (including vehicle crashes, disabled or stalled vehicles, spilled cargo, emergency or unscheduled maintenance, traffic diversions, or adverse weather), construction activities, scheduled maintenance activities, and major emergencies. Activities that increase demand include special events. Freeway traffic management strategies that mitigate capacity reductions include incident management; traffic control plans for construction, maintenance activities, special events, and emergencies; and minor design improvements (i.e. auxiliary lanes, emergency pullouts, and accident investigation sites). Freeway traffic management strategies to reduce demand include plans for incidents, special GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-17 events, construction, and maintenance activities; entry control/ramp metering; on-freeway HOV lanes; HOV bypass lanes on ramps; traveler information systems; and road pricing. Capacity Management Strategies - Incident management is the most significant freeway strategy generally used by operating agencies. Incidents can cause significant delays even on facilities that do not routinely experience congestion. It is generally believed that more than 50 percent of freeway congestion is the result of vehicle crashes. Strategies to mitigate the effects of vehicle crashes include early detection and quick response with the appropriate resources. During a vehicle crash, effective deployment of management resources can result in a significant reduction in the effects of the incident. Proper application of traffic control devices, including signage and channelization, is part of effective incident management. Quick removal of crashed vehicles and debris is another part. Incident management may also include the use of accident investigation sites on conventional streets near freeways for follow-up activities. Demand Management Strategies - The number of vehicles entering the freeway system is the primary determinant of freeway system performance. Entry control is the most straightforward way to limit freeway demand. Entry control can take the form of temporary or permanent ramp closure. Ramp metering, which can limit demand on the basis of a variety of factors that can be either preprogrammed or implemented in response to a measured freeway conditions, is a more dynamic form of entry control. Freeway demand can be delayed (changed in time), diverted (changed in space to an alternative route), changed in mode (such as HOV), or eliminated (the trip avoided). The difficult issue in assessing ramp metering strategies is estimating how demand will shift as a result of metering. HOV alternatives such as mainline HOV lanes or ramp meter by pass lanes are intended to reduce the vehicle demand on the facility without changing the total number of person trips. Assessing these types of alternatives also requires the ability to estimate the number of persons who make a change of mode to HOV. In addition, it is necessary to know the origin and destination of the HOV travelers to determine what portions of the HOV facility they can use, since many HOV facilities have some form of restricted access. Special events result in traffic demands that are based on the particular event. These occasional activities are amenable to the same types of freeway traffic management used for more routine activities such as daily commuting. In the case of special events, more planning and promotion are required than are typically needed for more routine activities. Road pricing is a complex and evolving freeway traffic management alternative. Initially, road pricing involved a user fee to provide a means to finance highways. More recently, toll roads have been built as alternatives to congestion. Now, congestion-pricing schemes are being implemented to manage demand on various facilities or in some cases to sell excess capacity on HOV facilities. The congestion-pricing approach to demand management is to price the facility such that demand at critical points in time and space along the freeway is kept below capacity by encouraging some users during peak traffic periods to consider alternatives. Nontraditional road pricing schemes are still in their infancy, so little information is currently available on their effects compared with more traditional toll roads, which view tolls only as a means to recover facility costs. 13.3. Arterial Traffic Analysis and Design Arterials are a functional classification of street transportation facilities that are intended to provide for through trips that are generally longer than trips on collector facilities and local streets. While the need to provide access to abutting land is not the primary function, the design of arterials must also balance this important need. To further highlight the often competing demands of urban arterials, it GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-18 should be recognized that other modes of travel such as pedestrians and public transit are also present and must be accommodated. To assure that arterials can safely provide acceptable levels of service for the design conditions, a number of design elements must be addressed. Since each design element is essentially determined based on separate analyses, the designer should then evaluate the entire arterial system and be prepared to refine certain elements to obtain an effective and efficient overall design. 13.3.1. Capacity Analysis and Level of Service (LOS) Capacity analysis is the key method to establish the number of travel lanes that will be needed to accommodate the design conditions. The design principles of this document are intended to be consistent with the methodology as outlined in the latest edition of the TRB Highway Capacity Manual (HCM). Capacity analysis software is essential to allow the designer to evaluate design alternatives in a timely manner. Several capacity analysis programs are acceptable, including The Highway Capacity Software (HCS), Synchro, and CORSIM. Other analysis packages should be discussed with the GDOT project manager prior to submitting as project documentation. When conducting capacity analysis, the analyst will use reasonable timing parameters. When the arterial has a number of signalized intersections that are spaced less 1,500-ft., then system operation is likely. In such cases, the capacity analysis will use the cycle length requirements from the critical intersection for all intersections. The traffic analysis will also consider pedestrian requirements. When significant pedestrian crossing volumes are expected, the capacity analysis will include minimum pedestrian intervals. The arterial LOS in the current HCM is based on the average travel speed for the segment, section or entire arterial under consideration. This is the basic measure of effectiveness (MOE). The design engineer should refer to the current HCM for detail discussion and description of LOS. The analysis method in the current HCM uses the AASHTO distinction between principal and minor arterials, but uses a second classification step to determine the design category for the arterial. The design criteria depend on factors such as: posted speed limit, signal density, driveway/access- point density, and other design features. The third step in the capacity analysis process is to determine the appropriate urban arterial class on the basis of a combination of functional category and design category. Refer to the HCM Chapter 10, for a detailed description of functional and design categories. 13.3.2. Traffic Analysis Procedures The traffic analysis and design generally includes the following elements: the typical section, access management, and intersection design. The following sections will address each of these areas. Determination of Typical Section To begin the conceptual design of an arterial, the number of travel lanes that are needed on the mid-block segments can be estimated based on ideal capacities. The ideal capacity of a two lane roadway is 1,700 vehicles per hour (vph) in each direction. The ideal capacity of a multi-lane roadway is 2,000 vph per lane. Capacity analysis should be used to check that acceptable levels of GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-19 service can be achieved with the selected typical section and the design traffic data. The following general guidelines are provided to assist in the process of establishing typical sections: Two-lane roadways are generally acceptable only if the DHV are less than 800 vph in either direction. Undivided multi-lane roadways are typically limited to areas where the posted speed limit is no greater than 40 mph and the DHV does not exceed 3,000 vph in either direction. Continuous two-way left turn lanes may be considered for roadways with typical sections having a number of closely spaced intersections with low-volume streets when the main roadway has no more than four lanes. Access Management Access management involves many techniques, ranging from zoning and subdivision regulations to highway design aspects and driveway access controls. For additional information related to Access Management, see Section 3.5. of this Manual. For additional information relating to driveway and access controls, including permit procedures, access criteria, and geometric design criteria, refer to the most current version of the GDOT Regulations for Driveway and Encroachment Control7. 13.3.3. Intersection Traffic Control and Design After the typical section is determined and the location of median breaks are determined (if the facility is divided), the traffic analysis should then focus on the intersections. It will be necessary to determine the type of traffic or right of way control and the need for turning lanes. Since the type of traffic control affects the intersection design, it is first necessary to determine if traffic signal control will be needed. An example of this influence on intersection design is that designers will typically limit the number of lanes on stop controlled approaches to avoid vehicles stopping abreast of each other and blocking sight distance from the other vehicle. When multiple lanes are needed on stop controlled approaches, the design will include islands and/or increased turning radii to separate through and turning vehicles. The need for traffic signal control is obvious at many intersections that are currently signalized. However, at other intersections traffic signal warrant analysis may be needed to establish the need for traffic signal control. At some intersections, where traffic signals are not currently needed, future traffic increases may warrant signal control. For such intersections, a warrant analysis should be conducted for both the construction year volumes as well as for the design year volumes. Warrant analyses should be conducted using the guidelines of the most current edition of the MUTCD. Signal warrants are typically conducted using hourly volumes throughout the normal day (not just peak hour volumes). Since the design volumes are limited to peak hour and daily volumes, it will be necessary to derive estimates of the volumes that occur during the remaining hours of the day. An important signal warrant is Warrant 1, Eight-Hour Vehicular Volume. Therefore, the traffic analysis should estimate the eighth-highest volume of the day. The eighth-highest volume can be compared to the requirement of Warrant 1 to estimate if this important warrant will be satisfied with the projected volumes. 7 GDOT. (2006). Regulations for Driveway and Encroachment Control. Available online at:http://www.dot.state.ga.us/dot/preconstruction/r-o-a-d-s/DesignPolicies/index.shtml GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-20 The eighth-highest volume can be estimated as representing 5.6 % of the daily volume. If the eighth-highest volume exceeds the minimum volumes for Warrant 1 using the construction year volumes, then signal control should be considered for installation during the construction project. If Warrant 1 is only met using the design year conditions, then signalization may not be included with construction, but the design may reflect the need for future signal control. For example, turn lanes may be constructed and striped out until signals are installed. Traffic Signal Permitting Process There are three distinct roadway systems in Georgia. These are the county roads, the city streets and the state routes. The Georgia Department of Transportation has authority over the state route system. Georgia Law empowers GDOT with the authority to set standards for all public roads in Georgia. Because traffic signals are used at many intersections where state routes cross city streets or county roads, and because traffic signals are most often installed to meet a Local community need, a permit process to allow local governments to erect, operate and maintain traffic signals on state routes has been established. This formal process has been ongoing since the early 1950's. The authority to create uniform regulations and to place or cause to place traffic control devices on state routes is described in section 32-6-50 of the Official Code of Georgia. Requests for traffic signals come to GDOT from a wide variety of sources. State, city and county elected officials responding to their constituents will often request GDOT to evaluate an intersection for a traffic signal. Requests may also be received directly into GDOT from concerned citizens. All inquiries are considered a request for assistance and should be investigated to determine if a signal or some less restrictive improvement should be implemented. Requests for signals are evaluated using the warranting values found in the MUTCD. These warrants will be the minimum criteria for further study. Intersection evaluations indicating a signal will not meet any warrant may be denied by a letter of response from the District Traffic Operations Office. Intersections that will meet one or more of the MUTCD warrants will be studied further for justification. All traffic signal devices erected on the state route system must have a permit application from the local government to GDOT and a Traffic Signal Authorization issued by GDOT prior to their installation. These permit documents serve as the agreement between GDOT and the local government for the signal. Even in communities where signals are maintained by GDOT, a formal document of agreement is needed. The permit application is used to allow the local government to formally request the use of a traffic signal. This application indicates the approval of the local government for the use of the signal. It also commits local government to provide electrical power and telephone service for the intersection. The Traffic Signal Authorization is the permit indicating the formal approval of GDOT for the use of the traffic signal at the intersection. Design drawings are a part of the authorization form showing the intersection details, the signal head arrangement, the signal phasing and the detector placement. Regardless of the method of funding and installation, a signal authorization is needed. The original of this authorization is kept in the Office of Traffic Operations with copies sent to the District Office and from the District Office to the local government for their records. Once a request is received, the District Traffic Engineer, using the methods described in the Manual on Uniform Traffic Control Devices, should initiate an engineering study. The study should first consider less restrictive measures such as improved signing, marking, sight distance, operational improvements, etc. If less restrictive measures can not be effectively implemented, a traffic signal GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-21 should be considered if the conditions at the intersection satisfy one or more of the warrants in the MUTCD. The completed Traffic Engineering Study shall have a signature page that includes the conclusions of the study and the recommendations of the District Traffic Engineer. Approval blocks should be included for the District Engineer (optional), State Traffic Engineer, and Division Director of Operations. Once completed, the Traffic Engineering Study will be sent to the Office of the Traffic Operations for review and approval. If the signal is found to be justified by the Traffic Engineering Study, a Traffic Signal Authorization will be recommended for approval by the State Traffic Engineer. A permit approval form will be prepared by the Office of Traffic Operations, and the entire package will be sent to the Division Director of Operations for recommendation and to the Chief Engineer of GDOT for final approval. A copy of the approved permit and the design will be returned to the District Traffic Operations Office for transmittal to the local government for their records. Signal permit revisions will be required for all changes made to the signal operation or design. Any addition of vehicle or pedestrian phases, modifications in phase sequences, modifications to signal head arrangements or other similar operational changes will require a permit revision. A request from the District outlining the changes needed and justifying the changes will be submitted in writing. A permit revision authorization will be issued with the appropriate design drawings similar to those required for a new signal. It is appropriate for new signals to be included in roadway projects if a need has been identified. Even in these circumstances the permit application, the signal authorization and Traffic Engineering Study are necessary for new signals to be installed in roadway projects. Existing signals requiring upgrading to meet the needs of the reconstructed roadway may be included in the construction project. A permit revision should be requested as outlined above. The Traffic Engineering Study prepared for the intersection proposed for signalization must adequately document two things. First, there is a need for this degree of control, and second, the analysis demonstrates that the signal operation will be beneficial to the state highway system. When these conditions are met, the State Traffic Engineer will recommend approval of the permit to the Division Director of Operations and Chief Engineer. The District Traffic Engineer should be the primary initiator for new signals on construction projects. This is to be accomplished as early in the project life as is possible, preferably at the design concept stage, and certainly should be accomplished by the preliminary field inspection (PFPR) since the use of signals will usually affect the roadway design. Due to the detrimental effect of traffic signals on the flow of arterial traffic a traffic signal may not always be to the benefit of the state highway system. Therefore, it is likely that signals which are justified by design year traffic volumes will be denied or deferred if initial traffic volumes do not warrant their inclusion in the project. The Traffic Engineering Study is even more important in this case as it will document conditions at a point in time and will assist in the decision making process to determine the right time to approve signalization. Pedestrian Accommodations at Signalized Intersections Crosswalks and pedestrian signal heads, including ADA considerations, shall be installed on all approaches of new traffic signal installations or revised traffic signal permits unless an approach prohibits pedestrian traffic. Exceptions may be granted if the pedestrian pathway is unsafe for pedestrians or the Traffic Engineering Study documents the absence of pedestrian activity. The District traffic engineer, project manager, consultant, local government, or permit applicant must GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-22 document the conditions and justification for eliminating pedestrian accommodations for each approach being requested. The documentation will be included in the permit file if accepted. In the case of one or more pathways being determined unsafe to cross at a signalized intersection, appropriate MUTCD signing prohibiting pedestrian traffic must be erected. Use of MUTCD signing may also be appropriate when it is necessary to restrict access to one pedestrian pathway. Prior to the Traffic Engineering Study recommending that pedestrian accommodations be eliminated based on the absence of pedestrian activity, the entity preparing the report should consider the existing development near the intersection, expected development within the next five year period, and input from local government. If any of these indicators project potential pedestrian activity the report should recommend pedestrian accommodations be included. Turn Lanes at Stop Controlled Intersections At stop controlled intersections, the number of lanes on the stop controlled approaches will normally be minimized. However, it may be desirable to provide a separate, channelized lane for the right turning traffic. It is desirable to provide separate lanes for vehicles that are preparing to turn off of the arterial roadway, when such turning volumes are significant. Guidelines for determining when such volumes are significant can be found in National Cooperative Highway Research Program (NCHRP) Evaluating Intersection Improvements: An Engineering Study Guide8, commonly referred to as NCHRP Report 457. Turn Lanes at Signal Controlled Intersections The need for turn lanes at signal controlled intersections can also be evaluated using the guidelines found in NCHRP 457. However, capacity analysis will also be the basis for establishing the need for turn lanes and determining when multiple turn lanes are needed. Although capacity analysis is used to identify potential needs for installing multiple turn lane bays, judgment must be used. For example, when providing dual left turn lanes, turn phases are generally operated in an "exclusive-only" manner. If dual turn lanes provide only marginal improvement over single turn lanes operated with protected/permitted phasing, it should be recognized that single turn lanes actually operate better during the off-peak times. After the need for turn lanes is established, it is then necessary to define the length of tapers and full storage. Capacity analysis will result in estimated lengths of queues. In general, full width storage will be provided that is sufficient to store the estimated queue lengths of turning vehicles. The traffic engineer will use judgment to evaluate the interaction of queues resulting from the different movements at the approach to an intersection. For example, left turn bays are sometimes "starved" due to the presence of long vehicle queues in the through lanes that block access to the left turn bay. When the estimated queue lengths of turning vehicles is less than but comparable to the queues for through vehicle, then the turn lane for the turn movement should be extended based on the queues in the through lanes. However, engineering judgment should be employed when making such decisions. As an example, if the through queues are estimated to be 800-ft. and the volume of left turn traffic is only 10 vph, then the left turn lane should not be extended to 800-ft. for such a small volume. 8 NCHRP. CHRP Report 457, "Evaluating Intersection Improvements: An Engineering Study Guide." 2001 GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-23 Drop Lanes When multiple turn lane bays are found to be needed on the arterial, it may be necessary to widen the intersecting roadway to accommodate an additional receiving lane. This widening should be extended to the next downstream intersection. However, as a minimum, the widening should be a sufficient distance downstream from the intersection in order to make the multiple turn lanes operate effectively and provide an adequate merging area. The additional lane may need to be expanded to the next downstream intersection. The traffic analysis will consider the distance that should exist on the receiving lanes prior to a lane drop. The length of this distance will affect the lane utilization and appropriate lane utilization factors will be included in the capacity analysis. The traffic analysis will provide a recommended length of widening based on the capacity analysis and the expected lane utilization. Highly Congested Urban Areas In many highly developed urban areas, it may be infeasible to meet the desirable level of service criteria. The following are examples: Capacity analysis indicates a high number of lanes (more than 6 lanes) needed to accommodate the design volumes Capacity analysis indicates grade separation would be required at major intersections The required improvements would require the acquisition and demolition of significant existing structures When the traffic analysis indicates that it will be infeasible to meet the LOS standard, these conditions will be documented in the traffic analysis. The traffic engineer will then prepare an incremental analysis. An incremental analysis will typically address each five-year period within the twenty-year design period. The traffic engineer must then request incremental traffic projections or assume linear increase throughout the design period. The incremental analysis will enable the traffic engineer to identify feasible improvements and report the expected operating conditions with these improvements at each incremental time period. 13.4. Trip Generation and Assignment for Traffic Impact Studies Trip Generation is the process used to estimate the amount of traffic associated with a specific land use or development. A manual estimate of trip generation from the development will be required for all analyses. Trip Assignment involves placing trips generated by the new development onto specific roadways and adding them to specific turning movements at each area intersection. 13.4.1. Trip Generation Data GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Table 13.2. Common ITE Land Use Codes ITE Land Use Code Land Use Name 210 Single Family Detached Housing 220 Apartment Traffic Forecasting 13-24 For the purposes of this Design Policy Manual, a trip is 310 Hotel a single vehicular movement with either the origin or destination within the study site and one origin or destination external to the land use. Trip generation is estimated through the use of "trip rates" or equations 520 Elementary School 565 Day Care Center 710 General Office Building that are dependent on some measure of intensity of 770 Business Park development of a particular land use. Gross leasable area (GLA) is the most common measure, but there are other measures such as number of employees, number of parking spaces, or number of pump islands (as at a 814 Specialty Retail Center 820 Shopping Center 832 High Turnover (Sit-Down) Restaurant gasoline station) that are included as well. 834 Fast Food Restaurant with Drive- Through Window The current ITE Trip Generation Handbook contains the most comprehensive collection of trip generation data available. The rates and equations provided in this 853 Convenience Market with Gasoline Pumps 912 Drive-In Bank handbook are based on nationwide data. Some rates or Source: ITE. (2003).Trip Generation Handbook, 7th Ed. equations, especially newer land use categories, are supported with a limited number of studies. However, this manual is accepted as the industry standard. Therefore, the rates and equations from the most current edition of the ITE Trip Generation Handbook shall be applied. Deviation from rates, equations, or applications described in most current edition of the Trip Generation Handbook must be discussed and approved by appropriate GDOT staff prior to use in any study. Trip generation data includes: Land Uses - Each land use type within Trip Generation is identified with a unique numeric land use code. Similar land use types have code numbers that are close together. Some of the more common ITE land uses are listed in the Table 3.2. Primary Trips, Passer-By Trips, and Diverted Trips The total trip generation volumes are typically computed as described previously and the generated trips are divided into these three components: Primary trips are made for the specific purpose of visiting the development. Primary trips are new trips on the roadway network. Passer-by trips are trips made as intermediate stops on the way from an origin to a primary destination. Passer-by trips are attracted from traffic already on adjacent roadways to the site. Diverted trips are similar to passer-by trips except that they are attracted to a development from a nearby street or roadway that is not directly adjacent to the development. Like passer-by trips, diverted trips are not new to the roadway system overall. However, unlike passer-by trips, diverted trips use new routes to get to and from the development compared to their original route and thus have more impacts to the nearby roadway network than passer-by trips. Study Network - The study network consists of the roadways in the vicinity of the development that traffic must use to enter and leave the study area. The study network includes the site access intersections onto adjacent off-site roadways and the sections of these off-site roadways that are located within the study area. The study network is further identified as a series of key intersections, which are the critical points and potential bottlenecks in urban and suburban roadway networks. Roadways within the study area can be further subdivided as described below. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-25 Site Access Points - These include key entrance roadways and driveways that serve the development and their intersections with the adjacent street and roadway network. These entrances/access points are usually newly constructed as part of the development. Existing Roadway Network - At a minimum, these are the streets and roadways that immediately adjoin the development. For larger developments, the network of streets and roadways to be included in the study can extend a considerable distance away from the immediate vicinity of the site. The key intersections along the roadways within the study area are the source of most delay and are what should be evaluated. The number and location of intersections that are to be included in the traffic impact study will be determined in consultation with GDOT prior to preparation of the study. Roadway Improvements Proposed as Part of Development - These include public streets and roadways that are proposed to be relocated, widened, or newly constructed as part of the proposed site development. The traffic assignment will take into account changes in traffic patterns caused by any proposed changes or additions to the roadway network. Committed Offsite Roadway Improvements - These include proposed roadway and intersection improvement projects that will be constructed by others within the time period of the study. The "others" are usually GDOT or local governments, but they could also include projects that will be constructed by other developers within the study area. Changes/improvements to roadways and intersections caused by these projects will be included in the traffic impact study. If it is uncertain whether or not a particular project will be completed, then alternative scenarios must be evaluated. Land Uses Not Identified in the ITE Trip Generation Manual The vast majority of real estate developments can be identified or approximated with land uses identified within Trip Generation. However, the commercial and residential real estate markets are constantly evolving, and new land use types, especially commercial and retail, are created all the time. Since Trip Generation is updated on a periodic basic, new land use categories are already in widespread use before being incorporated into Trip Generation. New types of "big-box" retail establishments are constantly being created that do not neatly fit in any single land use category included in Trip Generation. There are even new land use types that combine aspects of offices and warehouses and even retail. Large entertainment land uses such as casinos or theme parks may generate large numbers of trips, but are so specific as to not be covered by the more general land use categories included in Trip Generation. For land uses that are not found within Trip Generation, trip generation volumes can be estimated using other available information. However trip generation is estimated, each assumption must be clearly stated with backup information provided to the satisfaction of the reviewer. Permissible methods are listed below. Utilizing available marketing studies prepared by the client/developer Patronage estimates for rail/bus stations by transit agency Available parking spaces and assumptions on parking turnover per peak hour Using an existing ITE land use that most closely resembles the new land use, and modifying or adjusting generated trips, with all assumptions/calculations clearly stated 13.4.2. Traffic Assignment Traffic assignment is the process of placing site-generated trips onto the roadway network within the study area. Traffic assignment is done either manually or with modeling software. Traffic GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-26 assignment for small to medium sized developments is more commonly handled with manual methods, while modeling software is often used for larger developments that have a regional impact. The site-generated trips (usually vehicles per peak hour) are added to the "background" traffic, which usually consists of the existing peak hour turning movement volumes at each intersection plus additional turning movements which account for compounded annual growth and sometimes traffic attributed to other nearby developments. The combined site-generated and background traffic form the total assigned traffic (intersection turning movements) that is used to measure level of service and determine necessary roadway improvements to accommodate the new development. Traffic Assignment for Phased Developments Many large developments are constructed in several phases over a period of years. The traffic impact study can reflect this reality by analyzing one or more intermediate phases, plus the full build-out scenario. Each new phase will assign additional traffic onto the assumed roadway network for that year. Background traffic for each new phase must include traffic assigned from previously opened phases of development. Traffic Assignment of Three Major Trip Types The three major trip types are primary trips, passer-by trips, and diverted trips. Each trip type will be separated when assigning site-generated traffic throughout the study network. This makes it easier for the reviewer to follow the assignment process and identify errors. Primary trips are made for the specific purpose of visiting the development and they are new trips on the roadway network. Traffic will be assigned for primary trips throughout the study network according to the trip distribution percentages to and from the study area. Passer-by trips are trips made as intermediate stops on the way from an origin to a primary destination. Passer-by trips are attracted from traffic already on adjacent roadways to the site. These trips are separately assigned to the study network only at site-access intersections and on internal circulation roadways within the site development itself. Turning movement volumes will be added at these intersections for entering and exiting traffic, while the through movements will be reduced by an equal amount. Diverted trips are similar to passer-by trips except they are attracted to a development from a nearby street or roadway that is not directly adjacent to the site development. Like passer-by trips, diverted trips are not new to the roadway system overall, but their route will include off-site roadways and intersections on the study network. Like passer-by trips, these volumes will be deducted from the through traffic on the original roadway that they were traveling on, and the diverted volumes will be added to the revised route to and from the new developments. For more information on passer-by and diverted trips, please refer to the ITE Trip Generation Handbook, a companion to the ITE Trip Generation. The Handbook also includes helpful insight in preparing traffic impact studies, including studies for multi-use developments. GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-27 Chapter 13 Index Capacity Analysis. See Traffic, Analysis Capacity Level of Service (LOS). See Traffic, Analysis-Level of Service (LOS) Traffic Analysis - Arterials, 1824 Analysis - Capacity, 1314 Analysis - Freeway, 1218 Analysis Level of Service (LOS), 1415 Forecasting, 112 Management Strategies, 1618 GDOT Design Policy Manual ver. 2.0 Revised 05/21/2009 Traffic Forecasting 13-28 Chapter 14 Contents 14. LIGHTING 1 14.1. General Considerations 1 14.1.1. Roadway Lighting Warrants 1 14.1.2. Roadway Lighting Agreements 2 14.1.3. GDOT Assistance in Funding 3 14.1.4. No GDOT Assistance In Funding 4 14.1.5. Roadway Lighting Plan Preparation 5 14.2. Types of Lighting Projects 7 14.3. Illumination Requirements 7 14.3.1. Roadway 7 14.3.2. Vehicular Tunnels 7 14.3.3. Rest Areas and Welcome Centers 8 14.3.4. Park & Ride Lots and Pedestrian Tunnels 8 14.4. Lighting Calculations 8 14.5. Design Considerations 8 14.5.1. Standard Location Guidance 8 14.5.2. Luminaires 8 14.5.3. Electrical Materials 9 14.5.4. Roadway Lighting 9 14.5.5. Interchange Lighting 9 14.5.6. Truck Weigh Stations 12 14.5.7. Vehicular Tunnels 12 14.5.8. Rest Areas and Welcome Centers 12 14.5.9. Park & Ride Lots and Pedestrian Tunnels 12 14.5.10. Pedestrian and Security Lighting 12 14.6. Power Service 12 14.6.1. Grounding System 13 14.6.2. Photo Controls 15 Chapter 14 Index 16 Summary of Chapter 14 Revisions 17 List if Figures Figure 14.1. Example of a Lighting Gore Detail 11 Figure 14.2. Example of Service Point Single Line Diagram 14 GDOT Design Policy Manual ver. 2.0 Revised 01/09/2009 Chapter 14 Contents i 14. LIGHTING This chapter provides information on the various procedures and policies required for lighting future new construction and reconstruction projects and permitted lighting features on the state highway system in Georgia. It is not intended that existing lighting systems be modified as a result of the criteria outlined in this policy. GDOT has adopted the current edition of the American Association of State Highway and Transportation Officials (AASHTO) policy Roadway Lighting Design Guide for the state of Georgia. The remainder of this policy document will address items not included in the AASHTO guide or provide clarification or emphasis on included items. There are many reference publications that are available to the lighting designer, including but not limited to: AASHTO, Federal Highway Administration (FHWA), and the Illuminating Engineering Society of North America (IESNA) provide the most engineering information and knowledge in their handbooks and guides with regard to lighting design. Standard definitions of terms for lighting can be found in the AASHTO design guide. Refer to the References section of this manual for details on how to obtain these and other lighting reference publications. 14.1. General Considerations The Georgia Department of Transportation (GDOT) is generally responsible for providing lighting on state highways for the following purposes: roadway (corridor, and intersection/roundabouts) interchange tunnel (roadway, and pedestrian/multi use) underpass pedestrian (sidewalks, multi use paths, and streetscape) parking facilities (welcome centers, rest areas, truck weigh stations, and park and ride lots) aesthetics (enhancement projects, bridges, etc.) sign structures illumination of sign structures will be handled by the GDOT Office of Traffic Safety and Design and is not addressed in this document. 14.1.1. Roadway Lighting Warrants It is best that lighting requirements be coordinated at the concept stage. All lighting requirements for existing or proposed systems shall be coordinated with the Roadway Lighting Group of the GDOT Office of Road and Airport Design. Lighting should be considered for all Interstate projects (roadway and/or interchange), especially in urban areas, and be included in any interstate and or interchange upgrade project, assuming the local government will agree to the energy and maintenance costs for the newly installed system. GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-1 If while reconstructing existing roadways and/or adding lanes the proposed construction work does not conflict with existing roadway lighting structures, the new lane configuration still requires that the photometrics be evaluated based on current AASHTO and IESNA requirements. The majority will require a new lighting system to be provided. In addition, the lifespan of the major lighting system components (towers, poles, luminaires etc.) is typically 20 to 25 years. Retaining components longer can greatly increase the maintenance requirements of the lighting system. If an existing roadway lighting system is present and requires relocation, upgrade or replacement, then the required work for the lighting system will be included in the GDOT roadway project. The responsible Local Government shall continue to pay for Energy, Maintenance and Operations of the system. GDOT shall retain the ownership of the system. If no existing roadway lighting system is present AND the site does not meet the AASHTO warranting conditions for roadway lighting, THEN a written request for lighting must come from the Local Government for the inclusion of roadway lighting to be included in a programmed GDOT project to be considered. GDOT will include lighting with roadway projects or assist in the funding of lighting projects if requested by the local government and the local government will agree to the long term energy, maintenance and operations costs. 14.1.2. Roadway Lighting Agreements A lighting agreement and/or permit shall be required for all lighting facilities placed on GDOT's right of way. The Roadway Lighting Group prepares all lighting agreements for lighting included in all Let and Force Account projects. They also keep GDOT's archives for lighting agreements dating back to the late 1960's. Any inquiries to the existence of or the need for a new lighting agreement should be forwarded to the Roadway Lighting Group. The Office of Utilities will review all lighting permits as well as keeping the GDOT archives for all lighting permits. Any inquiries to the existence of a lighting permit should be forwarded to the Office of Utilities. For projects that have no GDOT funding, refer to Section 14.1.4. of this Manual. Lighting Agreements are not required for lighting GDOT owned and operated facilities such as welcome centers, rest areas and truck weigh stations. The Project Manager should coordinate through the Roadway Lighting Group for a local government lighting agreement or for any lighting requirements associated with their projects. Lighting agreements typically involve one local government, but multiple local governments may be involved (i.e. County and City). The physical location of the lighting system does not necessarily have to be within the jurisdictional area of the responsible local government. A local government may request to be responsible for a lighting system that is outside of their respective jurisdiction. Lighting Agreements are site specific, NOT construction project specific. Lighting Agreements cover a 50 year time period. This allows the Department to retouch the site multiple times without acquiring a new lighting agreement until such time that the agreement expires. Example: If the original agreement covered roadway lighting for a specific Interchange and GDOT reconstructs that Interchange and the proposed new lighting system matches the verbal description of the original agreement then no new agreement is required. But if the new project extends the coverage by GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-2 adding additional roadway lighting along the roadway (down mainline or crossroad) and no longer matches the verbal description in the existing agreement, then a new agreement would be required. 14.1.3. GDOT Assistance in Funding When GDOT and a Local Government enter into an Agreement to provide a roadway lighting system the project can be funded and constructed in accordance with one of the five basic scenarios of lighting projects. The four scenarios that include GDOT funding at various levels of participation are as follows: Scenario 1 Lighting system included in a GDOT let roadway or maintenance project Request for lighting assistance is received from the corresponding Local Government(s) and GDOT has an existing programmed project to which the work can be added and Local Government(s) sign a lighting agreement to pay for the energy, maintenance and operations of the lighting system Then the work is added to the GDOT project at no cost to the Local Government for design, materials and installation GDOT shall retain ownership of the lighting system This is the preferred scenario of GDOT Scenario 2 Lighting system included in a stand-alone force account lighting project Request for lighting assistance is received from the corresponding Local Government(s) and GDOT does NOT have an existing programmed project to which the work can be added and the site is on the National Highway System and a Cost Justification Report is provided showing it is more cost effective to install the lighting system via local government forces versus a Let project and the Local Government(s) sign a lighting agreement agreeing to be responsible for the design, installation, energy, maintenance and operations of the lighting system. Then a Stand-alone Force Account project can be set up with the Department being responsible for the funding of materials only GDOT shall retain ownership of the lighting system This is the second most commonly used scenario Scenario 3 Lighting system included in stand-alone local government-let lighting project Request for lighting assistance is received from the corresponding Local Government(s) and GDOT does NOT have an existing programmed project to which the work can be added GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-3 and the site is on the National Highway System and the Local Government(s) sign a lighting agreement agreeing to be responsible for the design, installation, energy, maintenance and operations of the lighting system Then a Stand-alone Local Government Let project can be set up with the Department being responsible for the funding of materials only GDOT shall retain ownership of the lighting system Scenario 4 Lighting system included in stand-alone GDOT-let lighting project Request for lighting assistance is received from the corresponding Local Government(s). and GDOT does NOT have an existing programmed project to which the work can be added. and the Local Government(s) sign a lighting agreement agreeing to be responsible for the energy, maintenance, and operations of the lighting system. and approval is received from GDOT Management. Then a Stand-alone Let GDOT project can be set up at no cost to the Locals for design, materials and installation GDOT shall retain ownership of the lighting system This scenario is used on a very limited basis and is for extreme circumstances approved on a case by case basis only 14.1.4. No GDOT Assistance In Funding In the event that GDOT will not be assisting in the funding, then a Utility Lighting Permit may be issued by GDOT with the Local Government or applicant being responsible for 100% of all associated costs while still meeting all state requirements for lighting design. The Department shall review and approve the plans. The Local Government or applicant retains ownership of the system under the following scenario. The scenario that includes no GDOT funding is as follows: Scenario - Utility Permit to Local Government or applicant for Lighting Roadway All lighting permits that are requesting to place lighting facilities on GDOT right of way are to be applied through appropriate District Utilities Office. The District Office will review and determine exactly what type of Lighting Permit has been received. There will be four different guidelines or types as follows: Residential Lighting Consisting of 1 or 2 luminaires only for purpose of lighting private property utilizing existing pole facilities. Applicant is paying for entire cost. District Utilities Office will review electrical hookups and District Traffic Operations Office will review the height of lights and position. Once reviewed and accepted by both the District Utilities and the District Traffic Operations offices, the District Engineer will approve the utility permit via the District Utilities Office. A copy shall be sent to the State Utilities Office. Business Lighting Consisting of 2 or more luminaires on existing pole facilities for the purpose of lighting private property with the Local Government or Applicant paying for entire GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-4 cost. District Utilities Office will review pole/light standard locations and electrical hookups and District Traffic Operations will review the height of lights and position. Once reviewed and accepted by both the District Utilities and the District Traffic Operations offices, the District Engineer will approve the utility permit via the District Utilities Office with a Special Provision that the Local Government or Applicant will design and construct the lighting in accordance with this Manual. If the request consists of 2 or more luminaires, on new pole facilities, for the purpose of lighting private property with the Local Government or Applicant paying for entire cost then the District Utilities Office will review pole/light standard locations and electrical hookups and District Traffic Operations will review the height of lights and position. The State Utilities Office will develop a Memorandum of Lighting Agreement to be signed by both parties (Local Government or Applicant and GDOT Management) before the utility permit can be approved. Once reviewed and accepted by both the District Utilities and District Traffic Operations offices and signatures have been received by the State Utilities Office, the District Engineer will approve the utility permit via the District Utilities Office with the Memorandum of Agreement attached. A complete copy of the approved utility permit (including the Memorandum of Agreement) shall be forwarded to the State Utilities Office. The State Utilities Office will forward a copy to the Roadway Lighting Section of the Office of Road and Airport Design. Governmental Lighting (Minor) - Consisting of a request to light a section of a state route that is not located on the National Highway System and the Local Government or Applicant is paying for the entire cost of the lighting system with no more than 4 luminaires. District Utilities Office will review pole/light standard locations and electrical hookups and District Traffic Operations Office will review the height of lights and position. State Utilities Office will develop the Memorandum of Lighting Agreement to be signed by both parties (Local Government or Applicant and GDOT Management) before the utility permit can be approved. Once reviewed and accepted by both the District Utilities and District Traffic Operations offices and signatures have been received by the State Utilities Office, the District Engineer will approve the utility permit via the District Utilities Office with the Memorandum of Agreement attached. A complete copy (including the Memorandum of Agreement) of the approved utility permit shall be forwarded to the State Utilities Office. The State Utilities Office will forward a copy to the Roadway Lighting Section of the Office of Road and Airport Design. Governmental Lighting (Major) - Consisting of a request to light sections of a state route that is not located on the National Highway System and the Local Government or Applicant is paying for the entire cost of the lighting system with 5 or more luminaires. District Utilities Office will review pole/light standard locations and electrical hookups and District Traffic Operations Office will review the height of lights and position. State Utilities Office will develop the Memorandum of Lighting Agreement to be signed by both parties (Local Government or Applicant and GDOT Management) and forward the complete permit package to the Roadway Lighting Section of the Office of Road and Airport Design for the review of the lighting plan. Once reviewed and accepted by all three Offices and signatures have been received in the State Utilities Office; the District Engineer will approve the utility permit via the District Utilities Office, with the Memorandum of Agreement attached. A complete original copy of the approved utility permit shall be forwarded to the State Utilities Office. The State Utilities Office will forward a copy to the Roadway Lighting Section of the Office of Road and Airport Design. 14.1.5. Roadway Lighting Plan Preparation The Office of Road & Airport Design's Roadway Lighting Group shall coordinate the preparation of lighting plans for all Let and Force Account projects for but is not limited to the following: GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-5 road design urban design consultant design all district offices Office of Maintenance other State agencies (i.e. Jekyll Island Authority) Local Governments (County and City) Lighting plans shall not be developed until after an executed lighting agreement is in place. All roadway lighting must be included GDOT's environmental evaluation processes. Most standalone lighting projects are handled with a Categorical Exclusion (CE) Environmental Document. This applies to Let or Force Account projects. For roadway projects that lighting is added to after the Environmental Document has been prepared, coordination with GDOT's Office of Environment/Location (OEL) is needed to ensure there are no historical or environmental conflicts. NEPA clearance can take up to 6 months to acquire dependent on the sensitivity of the site. Some examples of environmental and historical conflicts that can affect roadway lighting are: Endangered species: Sea turtles in coastal regions. Archeological conflicts: Indian mounds and other archeologically significant sites. Historic resources: Light trespass into historic districts or individual properties. Height restrictions adjacent to historic or individual properties. Environmental conflicts: Wetland impacts requiring directional bore in place of traditional trenching to run conduits. Possible restrictions as to the limits of vegetative clearing. The preparation of lighting plans that are to be included in a parent set of roadway or maintenance plans should not be started until AFTER the PFPR comments have been implemented into the roadway plans. The horizontal and vertical alignments, bridges plans, drainage, proposed utility plans etc. need to be set before the lighting plans can be developed. When requesting lighting plans for inclusion in parent project, a request must be sent to the Roadway Lighting Group with the following information: Confirmation of an executed Local Government Lighting Project Agreement (LGLPA) for the site (handled by request to the Roadway Lighting Group) Parent Project Number and PI Number Current Management Let Date Brief description of site and work to be covered by the lighting plans GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-6 Proposed delivery date for Final Lighting Plans The Roadway Lighting Group will prepare a scope and man hour estimate to include with each request for a Task Order Contract for lighting plans. After the Roadway Lighting Group has requested the Task Order and approval for the Task Order has been received; Program Delivery issues the Task Order through the Lighting Master Task Order Contract or through one of the general Master Task Order Contracts. Once the design consultant has been selected the following information will be required from the Project Manager: CD with the DGN files for the plan view covering the area to be lighted (minimum 1,000-ft. before the exit ramp gores and 1,000-ft. beyond the entrance gores along the interstate if interchange lighting). Full-size hardcopy set: cover, typical sections, plan, profile, drainage cross-sections/profiles, bridge plan and elevation (for all bridges located within the proposed lighting boundaries) and proposed utility plans. 14.2. Types of Lighting Projects Prior to the design of a lighting system, the designer must determine the project type and the particular location where lighting may be warranted. The following types of lighting projects are included and their design requirements discussed further in this chapter: roadway lighting interchange lighting truck weigh stations tunnels and underpass park and ride lots rest areas and welcome centers pedestrian and security lighting 14.3. Illumination Requirements If lighting is included in the project then the design shall be based upon AASHTO and IESNA guidelines, the designer should then determine the uniformity ratios and Light Loss Factors (LLF) for each specific lighting project. For roadways, tunnels, rest areas, welcome centers and park &ride lots, the guidance is as follows: 14.3.1. Roadway The roadway maintained average illuminance, uniformity ratio and veiling luminance ratio shall be in accordance with the AASHTO Roadway Lighting Design Guide and the IESNA RP-8. A LLF of 0.7 shall be used to compute the maintained illuminance values. The lighting designer may use a lower LLF if necessary but the designer shall document the reasons in the lighting calculations. 14.3.2. Vehicular Tunnels The maintained average luminance values in the tunnel threshold and interior zones shall be in accordance with the AASHTO Roadway Lighting Design Guide and the IESNA RP-22. A LLF of 0.5 GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-7 shall be used to compute the maintained luminance values. The lighting designer may use a lower LLF if necessary but the designer shall document the reasons in the lighting calculations. 14.3.3. Rest Areas and Welcome Centers The maintained average illuminance values for the parking and pedestrian areas shall be in accordance with the AASHTO Roadway Lighting Design Guide and the IESNA G-1. A LLF of 0.7 shall be used to compute the maintained illuminance values. The lighting designer may use a lower LLF if necessary but the designer shall document the reasons in the lighting calculations. 14.3.4. Park & Ride Lots and Pedestrian Tunnels The illuminance values for pedestrian tunnels shall be in accordance with IESNA G-1. A LLF of 0.7 shall be used to compute the maintained illuminance values. 14.4. Lighting Calculations As part of the steps for determining the appropriate lighting system for a particular project, the lighting designer must calculate the required illumination. Various factors are considered when making this determination, such as roadway width, lighting setback and mounting height, and the type of lighting system to be used. The designer determines the lighting calculations for a particular project by using a computer program, such as AGi32 by Lighting Analysts, Inc. The calculation shall show illuminance values on the roadway with point to point intervals of 6 ft. longitudinally and transversely. Also, when a section of roadway is being analyzed, the entire section of roadway that is being illuminated shall be analyzed completely as a self-contained area. The lighting calculations shall show the tabulated values for average, minimum and maximum footcandles, uniformity and veiling luminance ratios. The lighting designer shall submit files of the complete roadway or area under consideration with point by point illuminance values in Adobe Acrobat (.pdf) format. It may be necessary for the lighting designer to consider other lighting options and to substantiate that the lighting design is optimum and cost effective. The lighting designer shall be prepared to explain the lighting system choice and present all documentation to GDOT to substantiate the lighting recommendation. 14.5. Design Considerations This section provides guidance to the lighting designer with regard to roadways, interchanges, truck weigh stations, tunnels and underpasses, rest areas, welcome centers, park & ride lots, and pedestrian and security lighting. These design considerations, along with the lighting designer's experience and engineering knowledge of lighting design, should prove valuable in determining the most appropriate lighting system for each project. 14.5.1. Standard Location Guidance See Chapter 5, Roadside Safety and Horizontal Clearance, of this manual for locating light standards and high mast towers. In addition, light standards and high mast towers shall also be located to provide proper clearances from utility lines, airport glide paths, railroads, etc. The lighting designer shall ensure that the design is coordinated with other utility features. 14.5.2. Luminaires All luminaires shall be high pressure sodium and be in accordance with GDOT's Qualified Products List (QPL) and standard specifications. High mast luminaires with Type V symmetrical distribution is preferred. Other distributions may be used to accomplish proper roadway illumination or to avoid GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-8 spillage on adjacent properties. Cut-off optics shall be used for both high mast and conventional luminaires if required by project specific issues. 14.5.3. Electrical Materials All electrical materials, such as conduit, cables, wires and junction boxes, shall be new U.L. listed and meet the requirements of the National Electrical Code, and the American National Standards Institute. Electrical conduits, wires, circuit breakers, fuses, ground rods and ground conductors shall meet GDOT's Standard Specifications and shall be in accordance with GDOT's Qualified Products List (QPL). 14.5.4. Roadway Lighting Continuous roadway lighting generally uses conventional lighting systems consisting of high pressure sodium offset type luminaires. The use of mast arms with cobra head luminaires is discouraged and shall require approval on a case by case basis. The nominal mounting height shall be 30-ft. to 50-ft. The luminaries shall be 150W, 250W, or 400W depending on the roadway geometry and mounting heights. Lighting standards may be placed on one or both the sides of the highway either opposite each other or staggered. The lighting standard setback measured from the face of a non-mountable curb or edge of pavement to the centerline of the lighting standard shall be 5-ft. 6-in. minimum. Lighting standards located inside the clear zone shall be provided with AASHTO compliant breakaway transformer bases or breakaway couplings and breakaway wiring connectors unless shielded by a barrier. The lighting standards may also be located on the median barrier wall with specific approval from GDOT. GDOT will ensure that the maintenance on these luminaires will not pose an unacceptable level of safety or an unacceptable level of service if lane closures are required for lighting maintenance. Offset type luminaries with very short mast arms may be used for median barrier wall mounted lighting standards. Where it is more cost effective to do so, high mast lighting may be used for roadway lighting. 14.5.5. Interchange Lighting High mast lighting shall be used for interchange lighting unless the location has constraints on the pole height such as near airport boundaries. Conventional lighting may be used in the areas determined to have height constraints. At interchanges, the high mast poles shall have 100-ft. nominal mounting height. The high mast luminaries should be 1,000 Watt. Lower wattage luminaires may be utilized if satisfactory justification is first provided to GDOT. The lighting designer shall provide an optimum and cost effective lighting design for GDOT's approval. High mast lighting shall be provided to cover a minimum of 1,000-ft. from the farthest gore point on exit/entrance ramp. High mast lighting shall be provided to cover the distance to the point where the travel lane and taper is 12-ft. but shall not be less than 1,000-ft. from the gore point. (see Figure 14.1. Example of a Lighting Gore Detail). High mast luminaries with type V symmetrical distribution are preferred. Other types of light distributions may be used to accomplish proper roadway illumination or to avoid spillage on adjacent properties up to and including the use of offset luminaires. Shields shall be used to control light spillage on residences or other areas where the spilled light may be considered objectionable. The lighting designer needs to consider this type of impact to surrounding areas and land uses when developing the proper lighting system. GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-9 For high mast pole foundations, design analysis shall be performed. Soil borings shall be done at each proposed location of the high mast pole and the results used in the foundation design. The high mast pole foundation design shall be approved by the GDOT Office of Bridge Design prior to installation. High mast light poles located on a 2:1 or greater slope shall be provided with maintenance platforms. All underpasses within the illuminated limits of the interchange shall maintain the same illuminance levels as the adjacent roadway. This may require the installation of underpass luminaires. GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-10 Figure 14.1. Example of a Lighting Gore Detail GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-11 14.5.6. Truck Weigh Stations The truck weigh station shall be provided with a High Mast lighting system similar to the system described for interchange lighting. The entrance and exit ramps to the truck weigh station shall be provided with conventional lighting. See Section 14.5.5. of this Manual for the requirements of the limits of lighting coverage for the ramps. 14.5.7. Vehicular Tunnels The reflective characteristics of pavement, wall and ceiling materials shall be taken into account for computing roadway luminance values. The lighting designer shall also take into account daylight penetration into the tunnel. The luminaires shall preferably be mounted on the ceiling of the tunnel or shall be wall mounted. Specific approval shall be obtained from GDOT for ceiling mounting the luminaries. GDOT will ensure that the maintenance on these luminaires will not pose an unacceptable level of safety or an unacceptable level of service if lane closures are required for lighting maintenance. 14.5.8. Rest Areas and Welcome Centers The lighting for rest areas, welcome centers, and Park & Ride lots shall meet the requirements of IESNA RP-20 and G-1. Conventional lighting with high pressure sodium luminaires shall be used for all parking areas. High Mast Lighting shall be considered if the rest area or welcome center has large parking areas away from the buildings. Post top high pressure sodium luminaires shall be used in the picnic areas of rest areas and welcome centers. Conventional lighting with high pressure sodium luminaires shall be used for entrance and exit ramps into these special areas off the main highway. See Section 14.5.5. of this Manual for the requirements of the limits of lighting coverage for the ramps. 14.5.9. Park & Ride Lots and Pedestrian Tunnels Park & ride and pedestrian tunnels shall meet the requirements of IESNA G-1. All non tunnel mounted luminaires shall be full cut off or cut off HPS. All pedestrian tunnel luminaires shall be HPS and vandal proof. Cut-off optics shall be used if required by project specific issues. 14.5.10. Pedestrian and Security Lighting The pedestrian and security lighting shall meet the requirements of IESNA G-1. Conventional lighting shall be used. The lighting designer should consider the use of vandal-resistant luminaires and other electrical equipment for particular types of security lighting. 14.6. Power Service The lighting designer shall contact the power company and determine the availability of power service for lighting. A request shall be made to obtain the power service at locations desired by the lighting designer. The lighting designer shall provide the power company with information for estimated load at each service point location. A lighting site visit to meet with a power company representative may be necessary to coordinate power service for a roadway lighting project. The lighting designer shall coordinate with the power company and the local government or jurisdiction responsible for paying the utility bills to determine if the power services will be metered. GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-12 If the local government enters into a contract with the power company to provide power at a fixed monthly charge, light metering will not be required. The standard power services available from the power company are as follows: Single phase 3 wire: 120/240V and 240/480V, the latter is preferred. Three phase 4 wire: 480/277V. This power service is preferred when available for lighting projects with large loads. The electrical power distribution design shall meet the National Electrical Code and local codes. The power company may want to provide lighting contactors and photocells to control the lighting when the power service is not metered. In this case, the lighting designer shall include lighting contactors and photocell in the design to control the unmetered lighting system. All the electrical equipment, such as main circuit breakers, lighting contactors and load centers, shall be in NEMA-4X stainless steel enclosures that can be padlocked and shall be U.L. listed. A surge suppressor shall be provided at each power service. The surge suppressor shall be in NEMA-4X enclosure, UL1449 and UL1283 listed suitable for connection to the power service. The surge suppressor shall have a minimum surge current rating of 130,000A per phase and shall be provided with status indicating lights. The electrical equipment and distribution system shall be designed to take into account any possible future expansion. The electrical equipment short circuit ratings shall exceed the available fault current. The lighting designer shall obtain the available fault current values from the power company. The lighting designer shall size all the cables to limit the voltage drop to approximately 3.5%; and in no case more than a 5% drop in power service voltage. The voltage drop calculations shall be submitted to GDOT for approval. The lighting designer shall include a diagram of each service point. See Figure 14.2. Example of a Service Point Single Line Diagram, for an example of format and content. 14.6.1. Grounding System The ground rods shall be copper clad steel, minimum -in diameter, 10-ft. long. The buried ground conductors shall be stranded copper. All the underground connections in the grounding system shall be made using exothermic weld (cadweld) process. A ground rod shall be provided at each conventional light pole and connected in the pole base using a ground conductor. A ground grid consisting of four ground rods at the corners of the high mast lighting foundation shall be provided. The rods shall be connected to each other using #2 AWG stranded copper conductor to form a square ground grid. A #2 AWG bare stranded copper conductor shall be cadwelded to the grid and brought into the tower base to connect to the pole. A ground grid consisting of three ground rods located at the apexes of a 10-ft. equilateral triangle and connected to each other using #2 AWG stranded copper conductors shall be provided at each power service. An adequately sized stranded copper conductor shall be connected to the ground grid and routed to main service disconnecting means. Appropriately sized insulated ground conductor(s) shall be provided in the conduits with the branch circuits GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-13 Figure 14.2. Example of Service Point Single Line Diagram GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-14 14.6.2. Photo Controls All nighttime only lighting systems shall have a photocell control that operates independently of the power service provider controls. GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-15 Chapter 14 Index Illumination. See Lighting: Illumination Interchanges Lighting, 911 Lighting Design, 9 Lighting Calculations, 8 Funding No GDOT Assistance, 4 Funding GDOT Assistance, 3 Illumination Requirements, 7 Power Service, 1112 Project Types, 7 Roadway Lighting Agreements, 2 Roadway Lighting Plan Preparation, 5 Park & Ride Lots Illumination Requirements, 7 Lighting Design, 11 Pedestrian Lighting Design, 11 Lighting Design, 11 Rest Areas Illumination Requirements, 7 Lighting Design, 11 Roadway Illumination Requirements, 7 Lighting Design, 8 Security Lighting Design, 11 Truck Weigh Stations Lighting Design, 11 Tunnels Illumination Requirements, 7 Lighting Design, 11 Welcome Centers Illumination Requirements, 7 Lighting Design, 11 GDOT Design Policy Manual ver. 2.0 Revised 02/12/2009 Lighting 14-16 Glossaries EN-EX Entrance followed by exit (as in ramp terminals) Acronyms ETI Engineering Traffic Investigation (Report) 3R Roadway Resurfacing, Restoration, or Rehabilitation (Project) A/C Access Control AADT Average Annual Daily Traffic AAWT Average Annual Weekday Traffic AASHTO American Association of State Highway and Transportation Officials (http://www.transportation.org) ADA Americans with Disabilities Act ADDS Automated Data/Design Standards ADT Average Daily Traffic AHI Adjusted Hazard Index AREMA American Railway Engineering and Maintenance of Way Association (http://www.arema.org) ATR Automated Traffic Recorder AWG American Wire Gauge EX-EN Exit followed by entrance (as in ramp terminals) EX-EX Exit followed by exit (as in ramp terminals) FAA Federal Aviation Administration (http://www.faa.gov/) FDR Freeway Distributor Road FFPR (GDOT) Final Field Plan Review FHWA Federal Highway Administration (http://www.fhwa.dot.gov/) FRA Federal Railroad Administration (http://www.fra.dot.gov/) GDOT Georgia Department of Transportation (http://www.dot.state.ga.us) GLA Gross Leasable Area GRIP Governor's Road Improvement Program (http://www.dot.state.ga.us/DOT/planprog/planning/programs/grip/) AWT Average Weekday Traffic C-D Collector-Distributor CDR Collector Distributor Road GRTA Georgia Regional Transportation Authority (http://www.grta.org/) HCM Highway Capacity Manual (see References for additional information) CFR Code of Federal Regulations CL Centerline CORSIM Corridor Simulation Software CWP (GDOT) Construction Work Program dBA Decibels, A-Scale DHV Design Hour Volume DMS Dynamic Message System DTM Digital Terrain Model EN-EN Entrance followed by entrance (as in ramp terminals) HCS Highway Capacity Software (http://mctrans.ce.ufl.edu/hcs/) HOV High Occupancy Vehicle IES Illuminating Engineering Society IESNA Illuminating Engineering Society of North America (http://www.iesna.org) ISTEA Intermodal Surface Transportation Equity Act (http://www.bts.gov/laws_and_regulations/) ITE Institute of Transportation Engineers (http://www.ite.org/) Glossary of Acronyms 1 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 L/A Limited Access LARP Local Assistance Road Program LOS Level of Service LR Long Range LRFD (AASHTO) Load and Resistance Factor Design LRTP Long Range Transportation Plan MPO Metropolitan Planning Organization MUTCD Manual on Uniform Traffic Control Devices (FHWA) see References for additional information. NCHRP National Cooperative Highway Research Program (http://www4.nationalacademies.org/trb/crp. nsf) NHS National Highway System OCGA Official Code of Georgia (http://www.lexisnexis.com/hottopics/gacode/default.asp) OEL (GDOT) Office of Environment and Location (http://www.dot.state.ga.us/preconstruction/ oel/index.shtml) PDP (GDOT) Plan Development Process PE Preliminary Engineering PHF Peak Hour Factor PGL Profile Grade Line PI Point of Intersection (intersection of tangents to a curve) PC Point of Curvature (where a curve begins) PCC Portland Cement Concrete PFPR Preliminary Field Plan Review PHV Peak Hour Volume PM Preventive Maintenance PT Point of Tangent (where a curve ends) PVI Point of Vertical Intersection QPL (GDOT) Qualified Projects List RCInfo Roadway Characteristics Information RDG (AASHTO) Roadside Design Guide (https://bookstore.transportation.org/item_d etails.aspx?ID=148) ROR Run-off-Road (as in crash) ROW Right-of-Way RTV Right Turn Volume RV Recreational Vehicle SIDRA Signalized and Unsignalized Intersection Design and Research Aid SPUI Single Point Urban Interchange SRTA State Road and Tollway Authority STARS (Georgia) State Traffic and Report Statistics (http://www.dot.state.ga.us/dot/planprog/transportation_data/TrafficCD/index.sh tml) STIP Statewide Transportation Improvement Plan, also referred to as SWTP SWTP Statewide Transportation Plan (http://www.dot.state.ga.us/dot/planprog/planning/swtp/index.shtml) TAZ Traffic Analysis Zone TIP Transportation Improvement Program TL Travel Lane TOPPS Transportation Online Policy and Procedure System (http://www.dot.state.ga.us/topps/index.sht ml) TRB Transportation Research Board TWLT Two-Way Left Turn UAPSM (GDOT) Utility Accommodation Policy and Standards Manual. See References for additional information. Glossary of Acronyms 2 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 USGS United States Geological Survey (http://www.usgs.gov/) VE Value Engineering Vpd Vehicles per day WB Wheel Base (of a design vehicle) Glossary of Acronyms 3 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 Definition of Terms 3R Project A non-interstate resurfacing, restoration, or rehabilitation project. For additional information, see Chapter 11. Other Project Types 85th Percentile The speed at or below which 85 percent of the motor vehicles travel (FHWA MUTCD, 2003). AASHTO Green Book American Association of State Highway and Transportation Officials (AASHTO) publication named A Policy on Geometric Design of Highways and Streets. See References for additional information. Access Entrance to or exit from land adjacent to a public road. (GDOT Driveway Manual, 2004) Access Control see Control of Access Access Management Providing (or managing) access to land development while simultaneously preserving the flow of traffic on the surrounding road system in terms of safety, capacity, and speed. ADA (Americans with Disabilities Act) A federal law that was enacted in 1990 for the purpose of ensuring that all Americans have the same basic rights of access to services and facilities. The ADA prohibits discrimination on the basis of disability. To effect this prohibition, the statute required certain designated federal agencies to develop implementing regulations. Adjusted Hazard Index Rating the summation of the Unadjusted Hazard Index rating, the Adjustment Factor for School Buses, and the Adjustment for Train-Vehicle Crash history. (AHI = A5 + S + A) Aesthetics Consideration and/or evaluation of the sensory quality of resources (e.g. sight & sound). Approach Width: The half of the roadway that is approaching the roundabout. It is also referred to as approach half-width. Approved Bike or Bicycle Route See bicycle route, approved Arterial Functional classification for a street or highway that provides the highest level of service at the greatest speed for the longest uninterrupted distance, with some degree of access control. Arterial, Rural see Rural Arterial Arterial, Urban see Urban Arterial Asymmetrical Having a different configuration on either side of a centerline At Grade A crossing of two highways or a highway and a railroad at the same level. Attenuator A device used on roads and highways that acts as a buffer and absorbs the energy of a collision with an automobile. AutoTURN An advanced CAD-based software tool developed by TRANSoft Solutions used for analyzing and evaluating vehicle maneuvers for projects such as intersections, roundabouts, bus terminals, loading bays or any on or off-street projects that may involve access, clearance, and maneuverability checks. Additional information about AutoTURN ver 5.1 is available online at: http://www.transoftsolutions.com/transoft/pr oducts/at/product_overview.asp (TRANSoft, 2006). Auxiliary Lane See Lanes Auxiliary. Average Annual Daily Traffic (AADT) - The average 24-hour traffic volume at a given location over a full 365 day year. This means the total of vehicles passing the site in a year divided by 365. Average Daily Traffic (ADT) The total volume during a given time period (in whole Definition of Terms 1 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 days), greater than one day and less than a year, divided by the number of days in that time period (GDOT Driveway Manual, 2004). Average Annual Weekday Traffic (AAWT) The average 24-hour traffic volume occurring on weekdays over a full year. Average Weekday Traffic (AWT) - The average 24-hour traffic volume occurring on weekdays for some period of time less than one year. Axle Factor An adjustment factor that may be applied to traffic counts taken with portable traffic counters that account for two axle impacts as one vehicle. The Axle Factor provides for vehicles with more than two axles, such as trucks with three or more axles. Backwater "The increase in water surface elevation relative to the elevation occurring under natural channel and floodplain conditions induced upstream from a bridge or other structure that obstructs or constricts a channel (GDOT Manual on Drainage Design, 2005)." Base Conditions An assumed set of geometric and traffic conditions used as a starting point for computations of capacity and level of service (LOS). Base Year The year the project is completed and anticipated to be open for traffic use. Bicycle/Bike Route, Approved - any roadway where there is an existing bikeway or any location where a bicycle facility is identified for such roadway in a state, regional, or local transportation plan. Bifurcate An asymmetrical median that typically exceeds a normal median width where both directions of the roadway have independent alignments. The median area may be very wide and may contain natural vegetation and topography. Recommended for use on rural interstates and freeways. Big Box Retailer A large retail establishment (50,000+ sqft.) that is characteristic of a large windowless rectangular single-story building and large parking areas with few community or pedestrian amenities. Broken Back Curves See Curves: Broken Back Capacity the maximum hourly rate at which persons or vehicles reasonably can be expected to traverse a point or uniform segment of a lane or roadway during a given period under prevailing roadway, traffic, and control conditions. Centerline (1) For a two-lane road, the centerline is the middle of the traveled way; and for a divided road, the centerline may be the center of the median. For a divided road with independent roadways, each roadway has its own centerline. (2) The defined and surveyed line shown on the plans from which road construction is controlled. Center Turn Lane See Lanes: Center Turn Lane. Central Business District the commercial core of a city that can be typified by a concentration of commercial and retail land uses and the greatest concentration and number of pedestrians and traffic. Central Island See Island, Central Island Channelizing Island See Islands, Channelizing Island Chevron Alignment Sign Sign that is typically used on a roadway indicate alignment, a curve, or intersection. Chevron Alignment Signs are characterized by single or multiple reflectorized arrows. Circulatory Roadway: The roadway around the central island on which circulating vehicles travel in a counterclockwise direction. The width of the circulatory Definition of Terms 2 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 roadway depends mainly on the number of entry lanes and the radius of vehicle paths. Clear Zone The area beyond the roadway edge of travel which provides an environment free of fixed objects, with stable, flattened slopes which enhance the opportunity for reducing crash severity. For further clarification on the definition of Clear Zone, refer to the current edition of the AASHTO Roadside Design Guide. Cloverleaf Interchange See Interchanges, Cloverleaf Interchange. Collector Functional classification for a street or highway that provides a less highly developed level of service than an arterial, at a lower speed for shorter distances by collecting traffic from local roads and connecting them with arterials. Collector, Rural See Rural Collector. Collector, Urban - See Urban Collector. Collector-Distributor (CD) Road A parallel, controlled-access roadway that separates through traffic from local traffic that is entering and exiting the freeway or interstate system. CD roads are typically used to reduce conflicts associated with weaving. Consensus a general agreement among the members of a given group or community. Construction Standards A standard drawing published by GDOT and approved by FHWA. Control of Access Regulating access (ingress and egress) from properties abutting highway facilities. Full control of access Where preference is given to through traffic by providing access connections by means of ramps with only selected public roads and by prohibiting crossings at grade and direct driveway connections. Partial control of access Where preference is given to through traffic to a degree. Access connections, which may be at-grade or grade-separated, are provided with selected public roads and private driveways. CORSIM A comprehensive microscopic traffic simulation, applicable to surface streets, freeways, and integrated networks with a complete selection of control devices (i.e., stop/yield sign, traffic signals, and ramp metering). It simulates traffic and traffic control systems using commonly accepted vehicle and driver behavior models. (FHWA). Additional information about CORSIM can be found online at: http://ops.fhwa.dot.gov/trafficanalysistools/c orsim.htm Cross Section The transverse profile of a road showing horizontal and vertical dimensions. Cross Slope The rate of elevation change across a lane or a shoulder. Crown Normal Crown Roadway cross section which typically occurs when the roadway is a tangent section. No superelevation is present. Roadway cross slopes (typically 2%) in Georgia drain the roadway from either side of the pavement crown. The high point of the road is generally at the centerline or median, and the road slopes down from there. Reverse Crown Roadway cross slope that occurs when the normal crown slope (typically 2%) is continuous across a roadway section. This typically occurs as a normal part of a superelevation transition. Culvert Any structure under the roadway with a clear opening of 20 feet or less measured along the center of the roadway. Culverts are typically built to carry stormwater. Definition of Terms 3 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 Curb Cut Ramp A ramp that provides access between the sidewalk and the street for people who use wheelchairs which leads smoothly down from a sidewalk to a street, rather than abruptly ending with a curb and dropping roughly 4 to 6 inches (www.Wikepedia.org). Curves Broken Back Curves Successive curves in the same direction separated by a short tangent. Circular Curve A curve that has an arc of a constant radius. Note: most horizontal curves on Georgia roadways are circular curves. Compound Curve A curve that involves two horizontal curves of different radii sharing a common point for their PT and PC, respectively. Reverse Curve A curve consisting of two arcs of the same or different radii curving in opposite directions and having a common tangent or transition curve at their point of junction. The tangent section between the two arcs has 0 length. Spiral Curve see Transition Curve Transition Curve A curve of variable radius intended to effect a smooth transition from tangent to curve alignment, also known as a Spiral Curve. Vertical Curve A curve on the longitudinal profile of a road providing a change of gradient. Vertical curves are parabolic in shape. dBA The noise levels in decibels measured with a frequency weighting network, corresponding to the "A-Scale" on a standard sound level meter. Decision Sight Distance See Sight Distances: Decision Site Distance. Department, The The Georgia Department of Transportation. Departure Width - The half of the roadway that is departing the roundabout. It is also referred to as departure half-width. Design Exception A design condition that does not meet AASHTO guidelines and requires specific approval from FHWA to be built. Design Speed A selected speed used to determine the various geometric design features of a roadway. The maximum safe speed that can be maintained over a specified section of the road when conditions are so favorable that the design features of the road govern. Design Variance A design condition that meets AASHTO guidelines, but does not meet GDOT policy. A design variance requires specific approval from the GDOT Chief Engineer to be built. Design Vehicle A selected motor vehicle, the weight, dimensions, and operating characteristics of which are used as a control in road design. As defined by FHWA: the longest vehicle permitted by statute of the road authority (state or other) on that roadway (MUTCD, 2003). Design Volume A volume determined for use in design, representing the traffic expected to use the road. Design Year The anticipated future life of the project. For all GDOT projects, the design year is 20 years from the base year. Diamond Interchange See Interchanges, Diamond Interchange. Directional Interchange See Interchanges, Directional Interchange. Diverging Dividing a single stream of traffic into separate streams. Definition of Terms 4 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 Divided Highway A highway, street or road with opposing directions of travel separated by a median. Driver Expectancy What the typical driver would expect to encounter on a roadway. Easement Area where GDOT purchases the rights to perform work on a section of property, but does not acquire title to the property. Embankment An earthwork structure that raises the roadway higher than surrounding terrain. Free Flow Traffic flow in which the speed of any driver is not impeded. Free-Flow Speed The mean speed at which traffic travels when it is at free flow. Freeway A controlled access highway system that provides non-interrupted flow of traffic. Freeway Capacity - The maximum sustained 15-minute flow rate, expressed in passenger cars per hour per lane, that can be accommodated by a uniform freeway segment under prevailing traffic and roadway conditions in one direction of flow. Enhancements Aesthetic additions to a project, such as trees or streetscaping. Entry Radius: The minimum radius of curvature measured along the right curb at entry of a roundabout. Smaller radii may decrease capacity, while larger radii may cause inadequate entry deflection. Entry Width: The perpendicular distance from the right curb line of the entry to the intersection of the left edge line and the inscribed circle of a roundabout. Exit Radius: The minimum radius of curvature measured along the right curb at the exit of a roundabout. Exit Width: The perpendicular distance from the right curb line of the exit to the intersection of the left edge line and the inscribed circle. Exits should be easily negotiable in order to keep traffic flowing through the roundabout and accelerate out of it. Exit radii should then be larger than entering radii. Flat Spot Location in a superelevation transition where the pavement cross slope is 0% Footcandle The illumination of a surface with an area of one sqft. on which is uniformly distributed a flux of one lumen. A footcandle is equivalent to one lumen per square foot. Frontage Road "A road that segregates local traffic from higher speed through-traffic and intercepts driveways of residences, commercial establishments, and other individual properties along the highway (AASHTO Green Book, 2004, p. 339)." Functional Classification The grouping of all streets and highways according to the character of traffic service that they are intended to provide. There are three highway functional classifications: arterial, collector, and local roads. Geometric Design The arrangement of the visible elements of a road, such as alignment, grades, sight distances, widths, slopes, etc. GDOT Policy A guideline adopted by the Georgia Department of Transportation that must be followed. Glare Screen a partition, either continuous or a series of objects of such width and spacing, that is positioned on a median to block the glare from oncoming vehicle headlights. Gore The paved area of a roadway between two merging or diverging travel lanes. Travel within the gore area is prohibited. Grade (1) The profile of the center of the roadway, or its rate of ascent or descent. Definition of Terms 5 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 (2) To shape or reshape an earth road by means of cutting or filling. (3) Elevation. Grade Separation A crossing of two highways or a highway and a railroad at different levels. Green Book See AASHTO Green Book. Gutter Width Distance between the edge of traveled way and the face of curb. High Occupancy Vehicle Vehicles with two or more living, not pre-infant, persons. High Water The elevation of the highest known specific flooding event at a specific location. Highway A general term denoting a public way for purposes of vehicular travel, including the entire area within the right-ofway (NJDOT, 2006). Highway Section The part of the highway included between top of slopes in cut and the toe of slopes in fill (NJDOT, 2006). Horizontal Alignment Horizontal geometrics of the roadway. Horizontal Clearance The lateral distance measured either from the traveled way or the face of curb, to the face of a roadside object or feature. The rural shoulder is the part of the roadway beyond the edge of travel that is graded or paved flush with the edge of travel to allow for emergency usage (AASHTO Roadside Design Guide, 2006). Horizontal Curve A curve by means of which a road can change direction to the right or left. Human Factors Driving habits, ability of drivers to make decisions, driver expectance, decision and reaction time, conformance to natural paths of movement, pedestrian use and habits, bicycle traffic use and habits. Inscribed Circle: The circle formed just inside of the outer curb line of a circulatory roadway. Interchange Area where grade separated roadways are connected, and at least one roadway is free flowing. Cloverleaf Interchange An interchange that uses loop ramps to accommodate left-turns at an intersection and outer ramps to provide for the right turns. Diamond Interchange An interchange that connects a free flowing major road with a minor road. Diamond interchanges typically consist of four one-way diagonal ramps, one in each quadrant and two at-grade intersections on the minor road. The minor road has two stop signs, two signals, or one stop sign and one signal. Directional Interchange A free flowing interchange that allows vehicles to travel from one freeway to another freeway at relatively fast and safe speed. Semi-directional Interchanges An interchange that provides indirect connection between freeways yet more direct connection than loops. Service Interchange An interchange that connects a freeway to a lesser facility (such as a rest area or weigh station), as opposed to another freeway or minor road. Three Leg Interchange Also known as T or Y interchanges, this type of interchange is where a major highway begins or ends. System Interchange An interchange that connects a freeway to freeway. Single Point Urban Interchange (SPUI) An interchange that features a Definition of Terms 6 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 single traffic signal at the center of the interchange which controls all left turns. Opposing left-turn movements are completed simultaneously under the protection of this signal. Intersection The general area where two or more highways join or cross, including the roadway and roadside facilities for traffic movements within the area (AASHTO Green Book, 2004). Intersection Sight Distance See Sight Distances: Intersection Sight Distance. Islands: Devices used to separate or direct traffic in order to facilitate the safe and orderly movement of vehicles. An island may be a raised area that provides a physical barrier to channel traffic movements or a painted area. Specific types of islands include: Central Island The roundabout island around which traffic circulates. The central island may either be raised (nontraversable) or flush (traversable). Its size is determined by the width of the circulatory roadway and the diameter of the inscribed circle. The width of any truck apron provided is included in the central island width. Channnelizing Island - "At an intersection, the area defined by curbs, pavement markings, or unpaved areas formed by pavement edges for the purpose of directing traffic into defined paths, providing refuge areas for pedestrians or providing locations for traffic control devices (AASHTO Green Book, 2004)." Splitter Island: An island placed within the approach leg of a roundabout to separate entering and exiting traffic, provide a refuge for crossing pedestrians and bicyclists, and prevent wrong way movements. It is usually designed with raised curbing to deflect, and thereby reduce the speed of, entering traffic, and to provide a safer refuge. L10 A sound level that is exceeded 10 percent of the time for the period under consideration. This value is an indicator of both the magnitude and frequency of occurrence of the loudest noise events. Lane Balance The condition where the number of lanes leaving a diverge is one more than the number of lanes approaching the diverge. Lanes Acceleration Lane - A speed-change lane, including tapered areas, for the purpose of enabling a vehicle entering the roadway to increase its speed to a rate at which it can more safely merge with through traffic. Also called an "accel lane" (GDOT Driveway Manual, 2004). Auxiliary Lane The portion of the roadway adjoining the traveled way to help facilitate traffic movements: by providing for parking, speed change, turning, storage for turning, weaving, truck climbing, or for other purposes. Center Turn Lane A lane within the median to accommodate left-turning vehicles. Deceleration Lane A speed-change lane, including tapered areas, for the purpose of enabling a vehicle that is making an exit turn from a roadway to slow to a safe turning speed after it has left the mainstream of faster-moving traffic. Also called a "decel lane"; it denotes a right turn lane or a left turn lane into a development (GDOT Driveway Manual, 2004). Left Turn Lane A speed-change lane within the median to accommodate left turning vehicles. Inside Lane - On a multi-lane highway the extreme left hand traffic lane, in the direction of traffic flow, of those lanes available for traffic moving in one direction. Definition of Terms 7 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 Parking Lane An auxiliary lane primarily for the parking of vehicles. Passing Lane (1) A section of two-lane, two-directional road where sufficient clear sight distance exists to allow a safe passing maneuver to be performed. (2) An additional (third) lane that has been added to a two-lane roadway specifically for passing. Turn Lane A traffic lane within the normal surfaced width of a roadway, or an auxiliary lane adjacent to or within a median, reserved for vehicles turning left or right at an intersection. Traffic Lane The portion of the traveled way for the movement of a single line of vehicles in one direction. Letting The date GDOT opens sealed bids from prospective contractors. Level of Service A qualitative rating of a road's effectiveness relative to the service it renders to its users (from A-best to F-worst). LOS is measured in terms of a number of factors, such as operating speed, travel time, traffic interruptions, freedom to maneuver and pass, driving safety, comfort, and convenience. Lighting High Mast Roadway Lighting Illumination of a large area by means of a group of luminaires designed to be mounted in fixed orientation at the top of a high mast, generally 80 feet or higher (AASHTO Roadway Lighting Design Guide, 2005). Pedestrian Lighting Illumination of public sidewalks for pedestrian traffic generally not within rights-of-way for vehicular traffic roadways. Included are skywalks (pedestrian overpasses), sub-walks (pedestrian tunnels), walkways giving access to park or block interiors and crossings near centers of long blocks (AASHTO Roadway Lighting Design Guide, 2005). Roadway Lighting - Illumination of roadways by means of fixed luminaires in order to reduce driver conflict with other vehicles and pedestrians. Limited Access Facility A street or highway to which owner or occupants abutting land have little or no right of access. Local Road Functional classification that consists of all roads not defined as arterials or collectors; primarily provides access to land with little or no through movement. Longitudinal Barrier A barrier that is intended to safely redirect an errant vehicle away from a roadside or median hazard (CODOT, 2006) Loop Detector A traffic monitoring tool that is used to detect the presence of vehicles at an intersection to activate a traffic signal. Median The portion of a divided roadway separating the traveled ways for traffic in opposite directions (NJDOT, 2006). Median Crossover An opening constructed in the median strip of a divided highway designed to allow traffic movements to cross from one side of the highway to the other. In some cases, the Access Management Engineer may require the design to be such that some movements be physically prohibited (GDOT Driveway Manual, 2004). Median Width The overall width of a median measured from edge of travel lane to edge of travel lane. Merging The converging of separate streams of traffic to a single stream. Definition of Terms 8 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 Mitigation sequentially avoiding impacts, minimizing impacts, and compensating for any unavoidable impacts (WSDOT, 2005). Mitigation Plan document(s) that contain all information and specifications necessary to fully implement and construct a compensatory mitigation project (WSDOT, 2005). Nominal Safety A design alternative's adherence to design criteria and standards. Normal Crown See Crown: Normal Crown Operating Speed Actual speed at which traffic flows. Pace Speed The highest speed within a range of speeds (typically within 10 mph) that represents more vehicles than in any other like range of speed (FHWA MUTCD, 2003) Parametrics A modeling platform with application areas that include urban, highway, public transport, congested, free flow, ITS and HOV. Additional information about Parametrics is available online at: http://www.parametrics.com Parking Lane See Lanes: Parking Lane Passenger Car A passenger automobile with similar size and operating characteristics of a car, sport/utility vehicle, minivan, or pickup truck. Passing Lane See Lanes: Passing Lane. Passing Sight Distance See Sight Distances: Passing Sight Distance. Pavement Markings Devices or paint placed on the roadway to mark pavement for vehicular and pedestrian traffic control. Pedestrian Georgia State law defines a Pedestrian as: "Any person who is afoot" (GLC 40-1-1). By state definition, roller skaters, in-line skaters, skateboarders, and wheelchair users are also considered pedestrians. Pedestrian Refuge Also referred to as a refuge island/area or pedestrian island, is a section of pavement or sidewalk where pedestrians can stop before finishing crossing a road (www.wikipedia.org). Permit A legal document issued by the Department authorizing an applicant to do specific work on state rights-of-way (GDOT Driveway Manual, 2004). Posted Speed The speed limit posted on a section of roadway. Preventative Maintenance (PM) Projects the planned strategy of cost effective treatments to an existing roadway system and its appurtenances that preserves the system, retards future deterioration, and maintains or improves the functional condition of the system without increasing structural capacity. Profile A longitudinal section of a roadway, drainage course, etc. Profile Grade Line The point for control of the vertical alignment. Also, normally the point of rotation for superelevated sections (NJDOT, 2006). Project "A portion of a highway that a State proposes to construct, reconstruct, or improve as described in the Preliminary Design Report or applicable Environmental Document (FHWA VE Website, 2005)." Queue When one or more vehicles is traveling less than 7 mph. (SimTraffic, 2006) A vehicle is considered queued when it is either stopped at a traffic light or stop sign or behind another queued vehicle. Ramp Metering Use of a traffic control device for the intent of regulating the flow of traffic entering a freeway. The device, which is typically a traffic signal or a two-phase (red Definition of Terms 9 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 and green, no yellow) light, prevents multiple vehicles entering a freeway ramp. Reaction Time "The time from the onset of a stimulus to the beginning of a driver's (or pedestrian's) response to the stimulus, by a simple movement of a limb or other body part. (FHWA, 2001 http://www.tfhrc.gov/safety/pubs/97135/glos sary.htm#r)." Retaining Wall A structure that prevents dirt from sliding or eroding. Reverse Crown See Crown: Reverse Crown Reverse Curve See Curves: Reverse Curve Right-of-way (ROW or R/W) - All land under the jurisdiction of, and whose use is controlled by the Department (GDOT Driveway Manual, 2004). Right-of-Way Flares Areas needed for sight distance triangles at an intersection that should be kept free of obstructions in order to provide adequate sight distance. Roadside The area adjoining the outer edge of the roadway (NJDOT, 2006). Roadway The portion of a highway, including shoulders, for vehicle use (NJDOT, 2006). Roadway Characteristics The geometric characteristics of the freeway segment under study, including the number and width of lanes, right-shoulder lateral clearance, interchange spacing, vertical alignment, and lane configurations. Running Speed For all traffic, or a component thereof, the summation of distances traveled divided by the summation of running time. Rural Area "Those areas outside the boundaries of urban areas (AASHTO Green Book, 2004)." Rural Arterial Functional classification for a street or highway that integrates interstate and inter-county service, provides for movements between urban areas, and provides for relatively high travel speeds with minimum interference to through movement (AASHTO Green Book, 2004). Rural Collector - A street or highway that "generally serves travel of primarily intracounty rather than statewide importance and constitute those routes on which (regardless of traffic volume) predominant travel distances are shorter than on arterial routes. Consequently, more moderate speeds may be typical, on the average (AASHTO Green Book, 2004)." Rural Section Any roadway without curb and gutter. Rural Shoulder The part of the roadway beyond the edge of travel that is graded or paved flush with the edge of travel to allow for emergency usage. Semi-Directional Interchange See Interchanges, Semi-Directional Interchange Service Interchange See Interchanges, Service Interchange. Shoulder The portion of the roadway contiguous with the traveled way for accommodation of stopped vehicles, for emergency use, and for lateral support of base and surface courses (NJDOT, 2006). Shoulder Rumble Strip "A longitudinal design feature installed on a paved roadway shoulder near the travel lane. It is made of a series of indented or raised elements intended to alert inattentive drivers through vibration and sound that their vehicles have left the travel lane. On divided highways, they are typically installed on the median side of the roadway as well as on the outside (right) shoulder (FHWA, 2001, Roadway Shoulder Rumble Strips Technical Advisory Website Definition of Terms 10 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 http://www.fhwa.dot.gov/legsregs/directives/ techadvs/t504035.htm)." Sidewalk The portion of a street between the curb lines, or the lateral lines of a railway, and the adjacent property lines, intended for use by pedestrians (Georgia Code and Rules 40-1-1). Sight Distances The length of roadway ahead visible to a driver. Decision Sight Distance Sight distance that allows a driver to determine and complete the most efficient maneuver in response to an unexpected condition Intersection Sight Distance Sight distance needed for decisions at complex locations such as intersections. Values are substantially greater than Stopping Sight Distance. Passing Sight Distance Sight distance needed for passing other vehicles (applicable only on two-way, two-lane highways at locations where passing lanes are not present). Stopping Sight Distance - Sight distance needed for a driver to see an unexpected condition and stop the vehicle. At a minimum, Stopping Sight Distance is required at all locations on all roadways. Sight Distance Triangle Specified areas along intersection approach legs and across their included corners that should remain clear of obstructions. (AASHTO Green Book, 2004) Slope The face of an embankment or cut section; any ground the surface of which makes an angle with the plane of the horizon. Speed Design See Design Speed Speed Zone a section of highway with a speed limit that is established by law but which might be different from a legislatively specified statutory speed limit (FHWA MUTCD, 2003). Spiral See Curves: Transition Curve Standard Criteria having recognized and usually permanent values which are established formally as a model or requirement. Stopping Sight Distance See Sight Distances: Stopping Sight Distance. Superelevation The elevating of the outside edge of a curve to partially offset the centrifugal force generated when a vehicle rounds the curve. Superelevation Runoff "The length of roadway needed to accomplish a change in outside lane cross slope from zero (flat) to full superelevation, or vice versa (AASHTO Green Book, 2004, p. 175). " Superelevation (Tangent) Runout The longitudinal distance required to transition between normal crown and 0% cross slope (or vice versa). Superelevation Transition "The superelevation runoff and tangent run out sections (AASHTO Green Book, 2004, p. 175)." Sustained Grade A continuous road grade of appreciable length and consistent, or nearly consistent, gradient. Synchro software application used for traffic analysis, specifically to optimize traffic signal timing and perform capacity analyses. The software supports the Universal Traffic Data Format (UTDF) for exchanging data with signal controller systems and other software packages. System Interchange See Interchanges, System Interchange T Interchange - See Interchanges, Three-Leg Interchange Definition of Terms 11 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 Traffic Characteristics any characteristic of the traffic stream that may affect capacity, free-flow speed, or operations, including the percentage composition of the traffic stream by vehicle type and the familiarity of drivers with the freeway. Traffic Control Device A sign, signal, marking or other device placed on or adjacent to a street or highway by authority of a public body or official having jurisdiction to regulate, warn, or guide traffic. Traffic Lane See Lanes: Traffic Lane. Transfer Road A road that connects core roadways and C-D roads Transition A section of variable pavement width required when changing from one width of traveled way to a greater or lesser width. Transition Curve See Curves: Transition Curve Traveled Way The portion of the roadway provided for the movement of vehicles, exclusive of shoulders, auxiliary lanes and bicycle lanes (NJDOT, 2006). Truck Apron The mountable portion of a roundabout central island that is drivable specifically provided to accommodate the path of the rear left wheels of larger vehicles. Turn Lane See Lanes: Turn Lane. Turning Path The path of a designated point on a vehicle making a specified turn. Urban Area "Places within boundaries set by the responsible State and local officials having a population of 5,000 or more (AASHTO Green Book, 2004)." Urban Arterial Functional classification for a street or highway that serves urbanized areas and provides the highest level of service at the greatest speed for the longest uninterrupted distance, with some degree of access control. Urban Collector A street or highway that provides both land access service and traffic circulation within residential neighborhoods, commercial or industrial areas. It differs from the arterial system in that facilities on a collector system may penetrate residential neighborhoods, distributing trips from the arterials through the area to the ultimate destination. Conversely, the collector street also collects traffic from local streets in residential neighborhoods and channels it into the arterial system (AASHTO Green Book, 2004). Urban Roadway A roadway that is classified functionally as an Urban Arterial, Urban Collector, or Urban Local Street that operates at speeds generally less than or equal to 45 mph and features curb and gutter. Urban Shoulder The part of an urban roadway beginning at the edge of travel and extending to the breakpoint of the fore slope or back slope that ties to the natural terrain. Value Engineering "The systematic application of recognized techniques by a multi-disciplined team to identify the function of a product or service, establish a worth for that function, generate alternatives through the use of creative thinking, and provide the needed functions to accomplish the original purpose of the project, reliably, and at the lowest life-cycle cost without sacrificing safety, necessary quality, and environmental attributes of the project. (CFR Title 23 Part 627). " Variance See Design Variance. Vertical Alignment (Profile Grade) The trace of a vertical plane intersecting the top surface of the proposed wearing surface, usually along the longitudinal centerline of the roadbed, being either elevation or Definition of Terms 12 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 gradient of such trace according to the context. Vertical Curve See Curves: Vertical Curve. Weaving The crossing of two or more traffic streams traveling in the same general direction along a significant length of highway without the aid of traffic control devices (with the exception of guide signs). Weaving segments are formed when a merge area is closely followed by a diverge area, or when an on-ramp is closely followed by an off-ramp and the two are joined by an auxiliary lane. (TRB Highway Capacity Manual, 2000) Work Zone The work area and the section of highway used for traffic control devices related to the work area (NJDOT, 2006). Yield Line: A broken line marked across the entry roadway where it meets the outer edge of the circulatory roadway and where entering vehicles wait, if necessary, for an acceptable gap to enter the circulating flow. Y Interchange - See Interchanges, Three-Leg Interchange. Definition of Terms 13 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References Referenced Publications This section includes reference information, descriptions of publications, and where available, links to referenced publications. Publications are listed alphabetically by source. Page American Association of State Highway and Transportation Officials (AASHTO) 1 AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book). 2004 1 AASHTO. A Policy on Design Standards---Interstate System, 5th Edition. 2005 1 AASHTO. Guide for the Development of Bicycle Facilities, 3rd Edition. 1999 1 AASHTO. Guide for High-Occupancy Vehicle (HOV) Facilities, 3rd Edition. 2004 1 AASHTO. Guide for Park-and-Ride Facilities, 2nd Edition. 2004 1 AASHTO. Guide Specifications for Horizontally Curved Steel Girder Highway Bridges. 2003 2 AASHTO. Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT 400), 1st Edition. 2001 2 AASHTO. Highway-Rail Crossing Elimination and Consolidation. 1995 2 AASHTO. Roadside Design Guide, 3rd Edition. 2006. 2 AASHTO. Roadway Lighting Design Guide. 2005 2 AASHTO. Standard Specifications for Highway Bridges, 17th Edition. 2002 2 American Railway Engineering and Maintenance of Way Association (AREMA) 3 AREMA. Manual for Railway Engineering. 2006 3 Federal Highway Administration (FHWA) 3 FHWA. Americans with Disabilities Act (ADA) and Transportation Enhancements (TE). 2006 3 FHWA. Flexibility in Highway Design. 2004 3 FRA/FHWA. Guidance On Traffic Control Devices At Highway-Rail Grade Crossings. 2002 3 FRA/FHWA. Highway-Railroad Grade Crossings: A Guide to Consolidation and Closure. 1994 3 FHWA. Highway Traffic Noise in the United States - Problem and Response. 2006 3 FHWA. Manual on Uniform Traffic Control Devices (MUTCD). 2003 3 FHWA. Roundabouts: An Informational Guide FHWA-RD-00-67. 2000 3 FHWA. Value Engineering and The Federal Highway Administration (Website). 2005 3 FHWA. Roadway Lighting Handbook. 1978 3 Georgia Department of Transportation 3 GDOT. Bridge and Structures Policy Manual. 2006 GDOT. DRAFT Manual on Drainage Design for Highways. 2005 GDOT. Construction Standards and Details. 2006 GDOT. GDOT Context Sensitive Design Online Manual, Version 1.0. 2006 GDOT. Environmental Procedures Manual. 2006 GDOT. DRAFT Pavement Design Manual. 2005 GDOT. Pedestrian and Streetscape Guide. 2003 GDOT. Plan Development Process (PDP). 2006 GDOT. Plan Presentation Guide. 2002 GDOT. Regulations for Driveway and Encroachment Control. 2006 GDOT. GDOT Standard Specification Book. 2001 GDOT. Traffic Analysis and Design Manual. 2006 GDOT. Traffic Signal Design Guidelines. 2003 GDOT. Utility Accommodation Policy and Standards Manual. 1988 3 3 3 3 4 4 4 4 4 4 4 Error! Bookmark not defined.4 4 4 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References i Georgia Soil and Water Conservation Commission (GSWCC) 4 Georgia Soil and Water Conservation Commission. Manual for Erosion and Sediment Control in Georgia, 5th Edition. 2000 4 Illuminating Engineering Society of North America (IESNA) 5 IESNA. Guideline for Security Lighting for People, Property and Public Spaces (G-1-03). 2005 5 IESNA. Lighting Handbook, 9th Edition. 2000 5 IESNA. Lighting For Parking Facilities (RP-20-98). 1998 5 IESNA. Recommended Lighting for Walkways. 1994 5 IESNA. Recommended Lighting for Walkways and Class 1 Bikeways (DG-5-94). 1994 5 IESNA. Roadway Lighting ANSI Approved (RP-8-05). 2005 5 IESNA. Roadway Sign Lighting (RP-19 -01). 2001 5 IESNA/AHNSI. Tunnel Lighting (RP-22-05). 2005 5 Institute of Transportation Engineers (ITE) 5 ITE. Manual of Uniform Transportation Engineering Studies. 2000 5 ITE. Trip Generation Handbook, 7th Edition. 2003 6 National Cooperative Highway Research Program (NCHRP) 6 NCHRP. Design Speed, Operating Speed, and Posted Speed Practices [NCHRP Report 504]. 2003 6 NCHRP. Evaluating Intersection Improvements: An Engineering Study Guide [NCHRP Report 457]. 2001 6 NCHRP. Impacts of Access Management Techniques [NCHRP Project 3-52]. 1998 6 NCHRP. Modern Roundabout Practices [Synthesis 264]. 1996 Error! Bookmark not defined.6 NCHRP. Recommended Procedures for the Safety Performance Evaluation of Highway Features [Report 350]. 1992 6 National Fire Protection Association (NFPA) 6 NFPA. National Electrical Code [NFPA-70]. 2005 6 Texas Transportation Institute (TTI) 6 TTI. Grade Separations - When Do We Separate? Highway-Rail Crossing Conference. 1999 6 Transportation Research Board (TRB) 7 TRB. Highway Capacity Manual. 2000 7 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References ii American Association of State Highway and Transportation Officials (AASHTO) AASHTO. A Policy on Geometric Design of Highways and Streets (Green Book). 2004 This publication may be ordered online at: https://bookstore.transportatio n.org/item_details.aspx?ID=1 10 Notes: ISBN Number: 156051-263-6 "This fifth edition of AASHTO's `Green Book' contains the latest design practices in universal use as the standard for highway geometric design and has been updated to reflect the latest research on superelevation and side friction factors as presented in NCHRP Report 439" (AASHTO, 2006). AASHTO. A Policy on Design Standards--Interstate System, 5th Edition. 2005 This publication may be ordered online at: https://bookstore.transpor tation.org/item_details.as px?ID=100 Notes: ISBN Number: 156051-291-1 "Complements A Policy on Geometric Design of Highways and Streets and Standard Specifications for Highway Bridges. Topics include traffic design, right-of-way, geometric controls and criteria, cross section elements, interchanges, and bridges and other structures" (AASHTO, 2006). AASHTO. Guide for the Development of Bicycle Facilities, 3rd Edition. 1999 This publication in hard copy or CD format may be ordered online at: https://bookstore.transportatio n.org/ item _details.aspx?ID=104 development of new facilities to enhance and encourage safe bicycle travel. Planning considerations, design and construction guidelines, and operation and maintenance recommendations are included" (AASHTO, 2006). AASHTO. Guide for HighOccupancy Vehicle (HOV) Facilities, 3rd Edition. 2004 This publication may be ordered online at: https://bookstore.transportatio n.org/item_details.aspx?ID=1 14 Notes: ISBN Number: 156051-295-4 "This guide suggests methods and designs for dedicated facilities to encourage greater use of existing transportation systems, such as increased use of public transit (primarily buses), carpools, vanpools, or other ridesharing modes to help attain the above goals. Guidance is given for planning and design of preferential treatment for high-occupancy vehicles" (AASHTO, 2006). AASHTO. Guide for Parkand-Ride Facilities, 2nd Edition. 2004 This publication may be ordered online at: https://bookstore.transporta tion.org/item_details.aspx?I D=121 Notes: ISBN Number: 156051-294-6 "Information presented in this guide is intended to provide a general knowledge of the park-and-ride planning and design process. Applicable local ordinances, design requirements, and building codes must be consulted for their affect on the planning and design process. Local data resources, development patterns, and transit networks may present unique opportunities for parkand-ride implementation, and should be explored. Notes: "Supersedes the 1981 Guide for Development of New Bicycle Facilities. Provides information on the GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References 1 Chapter content includes: Defining the Park-and-Ride System, Park-and-Ride Planning Process, Operations and Maintenance of Park-and-Ride Facilities, Design Considerations for Park-and-Ride Facilities, and Architecture, Landscape, and Art: Integral Parts of the Park-and-Ride Facility" (AASHTO, 2006). AASHTO. Guide Specifications for Horizontally Curved Steel Girder Highway Bridges. 2003 Notes: [GHC-4] "Now with step-by-step design examples, this title supercedessupersedes the 1993 edition of Guide Specifications for Horizontally Curved Highway Bridges (formerly GHC-3). It reflects the extensive research on curved-girder bridges that has been conducted since 1980 and many important changes in related provisions of the straight-girder specifications" (Techstreet.com, 2006). This publication may be ordered online at: http://www.techstreet.com/cgibin/detail?product_id=1083781 AASHTO. Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT 400), 1st Edition. 2001 This publication may be ordered online at: https://bookstore.transportati on.org/item_details.aspx?ID= 157 Notes: "[This publication] addresses the unique design issues highway designers and engineers face when determining appropriate costeffective geometric design policies for very low-volume local roads. This approach covers both new and existing construction projects. Because geometric design guidance for very low-volume local roads differs from the policies applied to high-volume roads, these guidelines may be used in lieu of A Policy on Geometric Design of Highways and Streets, also known as the Green Book" (AASHTO, 2006). AASHTO. Highway-Rail Crossing Elimination and Consolidation. 1995 Explains the purpose and benefits of crossing consolidation from a national and local perspective, and from a highway and railroad perspective. Additional information regarding this publication is available online at: http://safety.transportation.org/prgpub.aspx?pid=1855 AASHTO. Roadside Design Guide, 3rd Edition. 2006. This publication may be ordered online at: https://bookstore.transportati on.org/item_details.aspx?ID= 148 Notes: ISBN Number: 156051-132-X "A synthesis of current information and operating practices related to roadside safety presented both in metric and U.S. customary units. The searchable CD-ROM of the text is included" (AASHTO, 2006). Includes March 2006 errata and also includes a revised Appendix A to accompany RSAP. This revised Appendix A is available for download at: http://downloads.transportation.org/RSDG-3Appendix%20A%20(revised).pdf AASHTO. Roadway Lighting Design Guide. 2005 Notes: [GL-6] This guide replaces the 1984 publication entitled An Informational Guide for Roadway Lighting. It has been revised and brought up to date to reflect current practices in roadway lighting. The guide provides a general overview of lighting systems from the point of view of the transportation departments and recommends minimum levels of quality. The guide incorporates the illuminance and luminance design methods, but does not include the small target visibility (STV) method. AASHTO. Standard Specifications for Highway Bridges, 17th Edition. 2002 Notes: "Replaces the 16th edition and its interims (19972003). The structural design standards used by state bridge engineers, engineering colleges and universities, and practicing engineers worldwide. Now features separate tables of contents for figures and tables. Updates provided on bridge web site for download and printing. For the first time, includes easy-to-use CD-ROM (HB-17-CDM)" (www.AASHTO.org). Additional information regarding this publication is available online at: https://bookstore.transportation.org/item_details.aspx?I D=51 GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References 2 American Railway Engineering and Maintenance of Way Association (AREMA) FHWA. Manual on Uniform Traffic Control Devices (MUTCD). 2003 Available online at: http://mutcd.fhwa.dot.gov/kno2003r1.htm AREMA. Manual for Railway Engineering. 2006 Notes: A new manual is published each year. The full manual or individual chapters may be ordered online through AREMA at http://www.arema.org Federal Highway Administration (FHWA) FHWA. Americans with Disabilities Act (ADA) and Transportation Enhancements (TE). 2006 Visit the following FHWA web page for additional information relating to Americans with Disabilities Act (ADA) requirements: http://www.fhwa.dot.gov/environment/te/te_ada.htm FHWA. Flexibility in Highway Design. 2004 Available online at: http://www.fhwa.dot.gov/envir onment/flex/ FRA/FHWA. Guidance on Traffic Control Devices at Highway-Rail Grade Crossings. 2002 Available online at: http://safety.fhwa.dot.gov/media/twgreport.htm FRA/FHWA. Highway-Railroad Grade Crossings: A Guide to Consolidation and Closure. 1994 Information regarding this publication is available online at: http://www.fra.dot.gov/downloads/Safety/gxlistofpubs20 06.pdf FHWA. Highway Traffic Noise in the United States Problem and Response. 2006 Available online at: http://www.fhwa.dot.gov/environment/probresp.htm FHWA. Roundabouts: An Informational Guide FHWARD-00-67. 2000 Available online at: http://www.tfhrc.gov/safety/00068.htm FHWA. Value Engineering and The Federal Highway Administration (Website). 2005 Available online at: http://www.fhwa.dot.gov/ve/index.cfm FHWA. Roadway Lighting Handbook. 1978 Notes: Implementation Package 78-15. Reprinted April 1984. Washington, D.C. Georgia Department of Transportation GDOT. Bridge and Structures Policy Manual. 2006 Available online at: http://www.dot.state.ga.us/dot /preconstruction/r-o-a-ds/DesignPolicies/ documents/pdf/GDOT%20Bri dge%20and%20Structures% 20Policy%20Manual.pdf GDOT. DRAFT Manual on Drainage Design for Highways. 2005 Available online at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/DesignPolicies /documents/pdf/GA8-ALL.pdf GDOT. Construction Standards and Details. 2006 Construction Standards and Details are available online at: http://tomcat2.dot.state.ga.us/stds_dtls/index.jsp GDOT. GDOT Context Sensitive Design Online Manual, Version 1.0. 2006 Available online at: http://www.dot.state.ga.us/csd GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References 3 GDOT. Environmental Procedures Manual. 2006 Available on the GDOT Repository for Online Access to Documentation and Standards (R.O.A.D.S.) website at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/DesignPolicies/documents/pdf/GDOT%20Environme ntal%20Procedures%20Manual.pdf GDOT. Pavement Design Manual. 2007 Provides guidance for developing the history and necessary information that may be needed in designing both a rigid and flexible pavement structure. Available online at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/DesignPolicies/documents/pdf/Pavement%20Design %20Manual.pdf GDOT. Pedestrian and Streetscape Guide. 2003 Provides direction to design professionals, developers, municipalities and others regarding the design, construction, and maintenance of pedestrian facilities. The Guide will also aid in continuing to address the goals put forth in GDOT's 1995 Bicycle and Pedestrian Plan. Available online at: http://www.dot.state.ga.us/dot/planprog/planning/projects/bicycle/ped_streetscape_guide/i ndex.shtml GDOT. Plan Development Process (PDP). 2006 Available on the GDOT Repository for Online Access to Documentation and Standards (R.O.A.D.S.) website at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/Other%20Resources/index.shtml GDOT. Plan Presentation Guide. 2002 Available on the GDOT Repository for Online Access to Documentation and Standards (R.O.A.D.S.) website at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/PPC/index.shtml GDOT. Regulations for Driveway and Encroachment Control. 2006 GDOT regulations, which are developed as guidelines for the maximum protection of the public through orderly control of traffic entering and leaving a part of the State highway system, updated October 2006. Available online at: http://www.dot.state.ga.us/dot/preconstruction/r-o-a-ds/DesignPolicies/index.shtml GDOT. GDOT Standard Specification Book. 2001 This publication may be ordered through the GDOT Office of Contract Administration at: http://tomcat2.dot.state.ga.us/ContractsAdministration/ The order form for this and other specification publications may be downloaded from: http://tomcat2.dot.state.ga.us/ContractsAdministration/u ploads/availpub.PDF GDOT. Traffic Signal Design Guidelines. 2003 Published by the GDOT Office of Traffic Safety and Design. Available online at: http://www.dot.state.ga.us/dot/operations/traffic-safetydesign/Documents/PDF/1.%20Traffic%20Signal%20De sign%20Guidelines.pdf GDOT. Utility Accommodation Policy and Standards Manual. 1988 Contains the current policy of the Georgia DOT Office of Utilities regarding utility accommodation on the public highway right-of-way. The three-part document and addenda are available online at: http://www.dot.state.ga.us/dot/operations/utilities/88ma nual.shtml Georgia Soil and Water Conservation Commission (GSWCC) Georgia Soil and Water Conservation Commission. Manual for Erosion and Sediment Control in Georgia, 5th Edition. 2000 Entire document (note: this is a 47.9 megabyte file, and will take several minutes to load on a high-speed Internet connection): http://s150378756.onlinehome.us/docs/green_book_5e d.pdf or Document index: GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References 4 http://gaswcc.georgia.gov/00/topic_index_channel/0,20 92,28110777_29155149,00.html#M Illuminating Engineering Society of North America (IESNA) IESNA. Guideline for Security Lighting for People, Property and Public Spaces (G-1-03). 2005 Guideline for design and implementation of security lighting, which covers basic security principles, illuminance requirements for various types of properties, protocol for evaluating current lighting levels for different security applications, and security survey and crime search methodology. Also includes exterior and interior security lighting practices for the reasonable protection of persons and property. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=1098026 IESNA.. Lighting Handbook, 9th Edition. 2000 Referred to by industry professionals as the "Bible of Lighting." This comprehensive reference includes explanations of concepts, techniques, applications, procedures and systems, as well as detailed definitions, tasks, charts and diagrams. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=229514 IESNA. Lighting For Parking Facilities (RP-20-98). 1998 A guideline for designing fixed lighting for parking facilities. Its recommendations only apply to the design of new lighting systems for parking facilities. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=14417 IESNA. Recommended Lighting for Walkways. 1994 A guideline for designing fixed lighting for parking facilities. Its recommendations only apply to the design of new lighting systems for parking facilities. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=14320 IESNA. Recommended Lighting for Walkways and Class 1 Bikeways (DG-5-94). 1994 Consolidates references made in previous IESNA publications with certain new information for designing lighting systems for walkways and Class I bikeways. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=14320 IESNA. Roadway Lighting ANSI Approved (RP-8-05). 2005 Provides the design basis for lighting roadways, adjacent bikeways, and pedestrian ways. This publication deals entirely with lighting and does not give advice on construction. It is not intended to be applied to existing lighting systems until such systems are redesigned. This publication revises and replaces the previous edition which was published in 1983 and reaffirmed in 1993. Publication may be ordered online through IES at: http://www.techstreet.com/cgibin/detail?product_id=739518 IESNA. Roadway Sign Lighting (RP-19 -01). 2001 A guideline that discusses elements of roadway sign lighting, both internally and externally lighted signs, as well as maintenance factors, sign surface reflectance and color change considerations. Publication may be ordered online through IESNA at: http://www.techstreet.com/cgibin/detail?product_id=926898 IESNA/AHNSI. Tunnel Lighting (RP-22-05). 2005 A guideline to assist engineers and designers in determining lighting needs, recommending solutions, and evaluating resulting visibility at tunnel approaches and interiors. Publication may be ordered online through IESNA at: http://www.techstreet.com/cgibin/detail?product_id=1260805 Institute of Transportation Engineers (ITE) ITE. Manual of Uniform Transportation Engineering Studies. 2000 Additional information and order forms for this publication are available online at: http://www.ite.org/tripgen/trippubs.asp GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References 5 Notes: "Shows in detail how to conduct several transportation engineering studies in the field. Discusses experimental design, survey design, statistical analyses, data presentation techniques, and report writing concepts. Provides guidelines for both oral and written presentation of study results. Includes useful forms for various transportation studies. Proceeded by the Manual of Traffic Engineering Studies" (www.ite.org, n.d.). ITE. Trip Generation Handbook, 7th Edition. 2003 Additional information and order forms for this publication are available online at: http://www.ite.org/tripgen/trippubs.asp Notes: "The 7th Edition of Trip Generation includes numerous updates to the statistics and plots published in the 6th Edition. A significant amount of new data has been collected and several new land uses have been added" (www.ite.org, n.d.). National Cooperative Highway Research Program (NCHRP) NCHRP. Design Speed, Operating Speed, and Posted Speed Practices [NCHRP Report 504]. 2003 Available online at: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_50 4.pdf NCHRP. Evaluating Intersection Improvements: An Engineering Study Guide [NCHRP Report 457]. 2001 An enhanced online version of the report is available at http://onlinepubs.trb.org/onlinepubs/ nchrp/esg/esg.pdf NCHRP. Impacts of Access Management Techniques [NCHRP Project 3-52]. 1998 This report may be ordered online through TRB's website at: http://www.trb.org/trbnet/projectdisplay.asp?projectid=7 97 NCHRP. Modern Roundabout Practices [Synthesis 264]. 1996 "This synthesis presents information on current practices with respect to the planning, design, and operation of modern roundabouts in the United States. It will be of interest to state and local highway design engineers, traffic engineers, maintenance engineers, as well as officials concerned with roadway safety. It will also be useful to design and traffic engineering consultants who may be assisting communities with the implementation of roundabouts" (www.TRB.org, n.d.). Available online at: http://trb.org/publications/nchrp/nchrp_syn_264.pdf NCHRP. Recommended Procedures for the Safety Performance Evaluation of Highway Features [Report 350]. 1992 This document is no longer in print, but may be accessed through the following link: http://safety.fhwa.dot.gov/roadway_dept/road_hardwar e/nchrp_350.htm. National Fire Protection Association (NFPA) NFPA. National Electrical Code [NFPA-70]. 2005 This Code covers the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for: (1) Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings (2) Yards, lots, parking lots, carnivals, and industrial substations FPN to (2). Publication may be ordered online at: http://www.nfpa.org/aboutthecodes/AboutTheCodes.as p?DocNum=70 or through the IENSA website at: http://www.techstreet.com/cgibin/detail?product_id=1160845 Texas Transportation Institute (TTI) TTI. Grade Separations - When Do We Separate? Highway-Rail Crossing Conference. 1999 Available online through the Texas Transportation Institute at: http://tti.tamu.edu/publications/catalog/ GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References 6 Transportation Research Board (TRB) TRB. Highway Capacity Manual. 2000 This publication may be ordered online at: http://trb.org/news/blurb_detai l.asp?id=1166 Notes: "TRB Special Report 209: Highway Capacity Manual, 3rd Edition is a collection of state-of-the-art techniques for estimating capacity and determining level of service for many transportation facilities and modes. The 3rd Edition of this manual was updated in 2000 as Highway Capacity Manual 2000" (TRB, 2006). GDOT Design Policy Manual Ver. 2.0 Revised 5/21/2007 References 7

State of Georgia

Department of Transportation

Pedestrian and

Streetscape Guide

Pedestrian and Streetscape Guide

Atlanta, Georgia 30308

This document was developed as part of the continuing effort to provide guidance within the Georgia Department of Transportation in fulfilling its mission to provide a safe, efficient, and sustainable transportation system through dedicated teamwork and responsible leadership supporting economic development, environmental sensitivity and improved quality of life. This document is not intended to establish policy within the Department, but to provide guidance in adhering to the policies of the Department. This is update #1.0 to GDOT’s Pedestrian and Streetscape Guide. Your comments, suggestions, and ideas for improvements are welcomed.

Please send comments to:

Traffic Operations Georgia Department of Transportation 935 East Confederate Ave., Bldg. 24 Atlanta , GA 30316

The Georgia Department of Transportation maintains this printable document and is solely responsible for ensuring that it is equivalent to the approved Department guidelines. All photographs by AECOM unless otherwise indicated.

Acknowledgements

AECOM and project staff would like to thank citizen advocates, design professionals, and elected officials for their ongoing support for pedestrian safety and involvement with updating the Guide.

Interview Sources External Stakeholders Local Agencies Corentin Auguin, Metropolitan Atlanta Rapid Augusta – Richmond County Transit Authority City of Decatur Brad Belo, Macon-Bibb County City of Norcross Kelly Cornett, Center for Disease Control City of Suwanee Sally Flocks, Pedestrians Educating Drivers on Safety City of Valdosta Amy Goodwin, Atlanta Regional Commission Cobb County Tamara Graham, City of Atlanta, Watershed Douglas County Management Emory University Shaun Green, Atlanta BeltLine Gwinnett County Sibetta Kakwete, Association of American Southern Georgia Regional Commission Retired Persons GDOT Jack Kittle, Citizen/Decatur David Adams Dee Merriam, Landscape Architect/Citizen Michelle Adejumo Byron Rushing, Atlanta Regional Commission Jack Anninos Kemberli Sargent, Pedestrians Educating Christina Barry Drivers on Safety Katelyn DiGioia Andrew Walter, City of Atlanta, Office of Mobility Iris Gorduk Daniel Pass Project Team Michelle Pate AECOM Toole Design Andrew Pearson Group Walt Taylor Jonathan DiGioia Ernie Boughman Scott Zehngraff John Hightower Erin Machell Robin Marshall Bonnie Moser Anna Nord Patrick Sweeney Mickey O’Brien Addie Weber Swati Babji Rao Marc Start

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Revision Summary

Revision Number Revision Date Revision Summary September 2003 Reformatted to new standard template 8/24/18 Updated GDOT logo throughout 3.0 4/25/19 Rewrite of manual

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List of Effective Chapters

Document Revision Number Revision Date List of Effective Chapters 3.0 4/25/19 Table of Contents 3.0 4/25/19 Acronyms 3.0 4/25/19 Chapter 1. Introduction 3.0 4/25/19 Chapter 2. GDOT Project Delivery 3.0 4/25/19 Chapter 3. Planning Streets for Pedestrians 3.0 4/25/19 Chapter 4. Road and Street Design for Pedestrians 3.0 4/25/19 Chapter 5. Traffic Signal Operations for Pedestrian Mobility 3.0 4/25/19 Chapter 6. Streetscape Design for Pedestrians 3.0 4/25/19 Chapter 7. Pedestrian Safety in Work Zones 3.0 4/25/19 Chapter 8. References 3.0 4/25/19 Appendix A. Mid-Block Pedestrian Crossing Evaluation 3.0 4/25/19 Appendix B. Landscape Maintenance Program (Sample) 3.0 4/25/19

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Table of Contents

Acknowledgements ...... i Interview Sources ...... i Project Team ...... i Revision Summary ...... iii List of Effective Chapters ...... v Table of Contents ...... vii Acronyms ...... xiii Introduction - Contents ...... 1-i 1.1 Intended Users of this Guide ...... 1-1 1.2 Relationship to Other Policies and Design Guidelines ...... 1-2 1.3 Navigating the Guide ...... 1-2 1.3.1 Application of Design Features ...... 1-3 1.3.2 Benefits of a Streetscape ...... 1-3 GDOT Project Delivery - Contents ...... 2-i 2.1 Plan Development Process and Plan Presentation Guide ...... 2-1 2.2 Design Variances and Exceptions ...... 2-3 Planning Streets for Pedestrians - Contents ...... 3-i 3.1 Prioritizing Presentation Safety ...... 3-1 3.1.1 Georgia Complete Streets Policy ...... 3-2 3.1.2 Public Right-of-Way Accessibility Guidelines (PROWAG) ...... 3-2 3.1.3 Georgia Pedestrian Safety Action Plan ...... 3-2 3.1.4 Georgia’s Policy of “Promoting Zero Pedestrian Deaths “ ...... 3-2 3.2 GDOT Complete Streets Policy...... 3-3 3.3 Connected Pedestrian Networks ...... 3-4 3.4 Pedestrian-Oriented Data Collection ...... 3-5 3.4.1 Compile Transportation and Site Development Plans ...... 3-6 3.4.2 Document Existing Infrastructure and Developments ...... 3-6 3.4.3 Observe Pedestrian Activity ...... 3-7 3.5 Context-Sensitive Design for Pedestrian Facilities ...... 3-8 3.5.1 Tactics for Involving the Community ...... 3-9 3.5.2 Street Types and Adjacent Land Uses ...... 3-11 Road and Street Design for Pedestrians - Contents ...... 4-i 4.1 Vehicle Speeds ...... 4-1 4.1.1 Relationship among Vehicle Speed, Pedestrian Comfort, and Injuries ...... 4-1 4.1.2 Posted, Design, and Target Speed ...... 4-2

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4.2 Traffic Calming ...... 4-3 4.2.1 Chicanes ...... 4-5 4.2.2 Curb Extensions ...... 4-7 4.2.3 Lane Shifts ...... 4-9 4.2.4 Pinch Points ...... 4-10 4.2.5 Radar Speed Signs ...... 4-12 4.2.6 Signal Progression ...... 4-13 4.2.7 Speed Cushions ...... 4-14 4.2.8 Speed Bumps ...... 4-15 4.2.9 Speed Tables...... 4-17 4.2.10 Two-Way Streets ...... 4-20 4.3 Optimizing the Cross Section for Pedestrians ...... 4-20 4.3.1 ADA Ramps and Detectable Edges ...... 4-20 4.3.2 Bicycle Facility Infrastructure ...... 4-22 4.3.3 Handrails and Safety Railings ...... 4-26 4.3.4 Fencing for Pedestrian Access Control ...... 4-28 4.3.5 On-Street Parking ...... 4-28 4.3.6 Pedestrian Accommodations along Bridges and Constrained Rights-of-Way ...... 4-31 4.3.7 Raised Medians and Pedestrian Refuge Areas ...... 4-32 4.3.8 Roadway and Lane Diets ...... 4-35 4.3.9 Shared Streets ...... 4-38 4.3.10 Shared Use Paths ...... 4-39 4.3.11 Sidewalks ...... 4-44 4.3.12 Transit Stops...... 4-50 4.4 Intersection Design ...... 4-52 4.4.1 Channelized Right-Turn Lanes ...... 4-53 4.4.2 Corner Extensions ...... 4-56 4.4.3 Corner Radii ...... 4-57 4.4.4 Curb Ramps ...... 4-59 4.4.5 Diverging Diamond Interchanges ...... 4-61 4.4.6 Diverters ...... 4-63 4.4.7 Driveway Crossings ...... 4-66 4.4.8 Marked Crosswalks...... 4-68 4.4.9 Pedestrian Bridges and Underpasses ...... 4-72 4.4.10 Protected Intersections ...... 4-75 4.4.11 Raised Crosswalks ...... 4-77 4.4.12 Raised Intersections ...... 4-79 4.4.13 Roundabouts ...... 4-80 Rev. 3.0 Table of Chapters 4/25/19 Page viii Pedestrian and Streetscape Guide

4.4.14 Single-Point Urban Interchanges ...... 4-83 4.4.15 Skewed Intersections ...... 4-84 Traffic Signal Operations for Pedestrian Mobility - Contents ...... 5-i 5.1 Signal Timing Strategies for Pedestrians ...... 5-1 5.1.1 Pedestrian Recall ...... 5-1 5.1.2 Leading Pedestrian Interval ...... 5-2 5.1.3 Pedestrian Scramble ...... 5-3 5.1.4 Shorter Vehicular Cycle Lengths ...... 5-4 5.2 Pedestrian Infrastructure at Traffic Signals ...... 5-5 5.2.1 Pedestrian Detection Devices ...... 5-5 5.2.2 Accessible Pedestrian Signals and Detectors ...... 5-6 5.3 Traffic Control Devices for Uncontrolled Pedestrian Crossing Locations ...... 5-7 5.3.1 Rectangular Rapid Flashing Beacon ...... 5-7 5.3.2 Pedestrian Hybrid Beacons ...... 5-9 Streetscape Design for Pedestrian - Contents ...... 6-i 6.1 Utilities ...... 6-2 6.2 Sidewalk Zones ...... 6-3 6.2.1 Frontage Zone ...... 6-4 6.2.2 Pedestrian Circulation Zone ...... 6-5 6.2.3 Greenscape/Furniture Zone ...... 6-7 6.3 Components of a Streetscape/ Urban Design Elements ...... 6-10 6.3.1 Hardscape ...... 6-10 6.3.2 Bike Parking ...... 6-11 6.3.3 Bollards ...... 6-16 6.3.4 Pedestrian-Scale Lighting ...... 6-17 6.3.5 Seating ...... 6-20 6.3.6 Transit Stop Amenities ...... 6-22 6.3.7 Trash Receptacles ...... 6-26 6.3.8 Wayfinding Signage ...... 6-27 6.4 Green Stormwater Infrastructure ...... 6-31 6.4.1 Bioretention Planters ...... 6-33 6.4.2 Biofiltration Planters ...... 6-34 6.4.3 Grassed Swales ...... 6-34 6.4.4 Permeable Pavement ...... 6-34 6.5 Tree and Plant Considerations ...... 6-36 6.5.1 Tree and Plant Selection ...... 6-36 6.5.2 Hardiness Zones of Georgia ...... 6-38

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6.5.3 Infrastructure for Healthy Root Systems ...... 6-39 6.5.4 Horizontal Clearances for Trees and Shrubs ...... 6-41 6.5.5 Tree and Plant Approval Prior to Installation ...... 6-43 6.5.6 Tree Protection during Construction ...... 6-43 Pedestrian Safety in Work Zones - Contents ...... 7-i 7.1 Temporary Traffic Control and Detour Plans ...... 7-1 7.2 Components of an Accessible Work Zone ...... 7-3 7.2.1 Separation Devices ...... 7-3 7.2.2 Sidewalk Closure and Detour Signs ...... 7-3 7.2.3 Temporary Pedestrian Crossings ...... 7-4 7.2.4 Temporary Pedestrian Walkways ...... 7-4 7.3 Maintenance of Pedestrian and Bicycle Infrastructure in Work Zones ...... 7-6 References - Contents ...... 8-i Appendix A. Mid-Block Pedestrian Crossing Evaluation ...... A-1 A.1 Introduction ...... A-1 A.1.1 Goals of this Guide ...... A-1 A.1.2 Agency Application ...... A-1 A.2 Pedestrian Crossing Evaluation Process Overview ...... A-2 A.2.1 Evaluation Process Overview ...... A-2 A.2.2 Documenting the Pedestrian Crossing Evaluation ...... A-2 A.2.3 Evaluating the Safety of Existing Pedestrian Crossings ...... A-18 A.3 Pedestrian Crossings at Uncontrolled Locations Template Engineering Study ...... A-20 A.3.1 GDOT Complete Streets Policy Pre-screening Form ...... A-21 2. Data Collection Sheets ...... A-22 A.3.2 Evaluating the Safety of Existing Pedestrian Crossings ...... A-27 Appendix B. Landscape Maintenance Program...... B-1 B.1 Example of a Landscape Maintenance Program ...... B-1 B.2 Safety and Chemical Use ...... B-1 B.3 Specifics Related to Pruning ...... B-1 B.4 Typical Monthly Landscape Maintenance Guidelines ...... B-2

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AASHTO American Association of State Highway and Transportation Officials ADA Americans with Disabilities Act APBP Association of Pedestrian and Bicycle Professionals ARC Atlanta Regional Commission BMP Best Management Practice CRZ Critical Root Zone DBH Diameter at Breast Height DDI Diverging Diamond Interchange FHWA Federal Highway Administration GDOT Georgia Department of Transportation GEPA Georgia Environmental Policy Act HDOT Hawaii Department of Transportation ISA International Society for Arboriculture ITE Institute of Transportation Engineers LAP Local Administered Project LPI Leading Pedestrian Interval mph miles per hour MS4 Municipal Separate Storm Sewer System MUTCD Manual on Uniform Traffic Control Devices NACTO National Association of City Transportation Officials NCHRP National Cooperative Highway Research Program NEPA National Environmental Policy Act PEDS Pedestrians Educating Drivers on Safety PHB Pedestrian Hybrid Beacon PROWAG Proposed Right-of-Way Accessibility Guidelines R.O.A.D.S Repository for Online Access to Documentation and Standards RRFB Rectangular Rapid Flash Beacon SPUI Single-point Urban Interchange TPZ Tree Protection Zone

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Introduction - Contents

Introduction - Contents ...... 1-i 1.1 Intended Users of this Guide ...... 1-1 1.2 Relationship to Other Policies and Design Guidelines ...... 1-2 1.3 Navigating the Guide ...... 1-2 1.3.1 Application of Design Features ...... 1-3 1.3.2 Benefits of a Streetscape ...... 1-3

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Introduction

The Georgia Department of Transportation (GDOT) Pedestrian and Streetscape Guide contains guidelines and best practices for the design of streets and roadways that support safe multimodal travel. As defined by the Federal Highway Administration (FHWA), a pedestrian is “Any person not in or on a motor vehicle or other vehicle. Excludes people in buildings or sitting at a sidewalk cafe.” The National Highway Traffic Safety Administration also uses another pedestrian category to refer to pedestrians using conveyances and people in buildings. Examples of pedestrian conveyances include skateboards, non-motorized wheelchairs, roller skates, sleds, and transport devices used as equipment. The Guide focuses on design of pedestrian and streetscape facilities, but good design is one component of a successful pedestrian facility. Conscientious planning, effective education programs, and consistent safety and law enforcement also contribute to improving our communities for everyone. Some guidance related to planning for people who walk is provided, but the overall intent is to encourage good design practices. Further guidance is provided in Appendix A for locating mid- block crossings.

1.1 Intended Users of this Guide The anticipated users include planning and design practitioners, elected officials, developers, advocates, and public works departments, as well as others listed in Figure 1.1. The Guide provides information on how to design pedestrian infrastructure, build out a connected pedestrian network, and create a comfortable environment for people to walk.

Figure 1.1. Anticipated Users of the Pedestrian and Streetscape Guide

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1.2 Relationship to Other Policies and Design Guidelines This Guide builds upon the design guidelines and standards set forth in the GDOT Design Policy Manual and the US Access Board Public Right-of-Way Accessibility Guidelines (PROWAG) by providing supplemental recommendations for enhancing pedestrian infrastructure beyond the minimum standards. The recommendations in this Guide do not supersede the policies established in the GDOT Design Policy Manual or PROWAG. The recommendations in this Guide were compiled from numerous local, state, and national sources. The sources are referenced throughout the Guide and detailed in Chapter 8. The following list provides the main sources that were consulted in the development of the Guide.

(From top left) American Association of State Highway and Transportation Officials (AASHTO) Roadside Design Guide (latest edition)

AASHTO A Policy on Geometric Design of Highways and Streets (“Green Book”) (latest edition)

FHWA Manual on Uniform Traffic Control Devices for Streets and Highways (latest edition)

GDOT Context Sensitive Design Online Manual (latest edition)

GDOT Design Policy Manual (latest edition)

GDOT Plan Development Process (latest edition)

AASHTO Guide for the Development of Bicycle Facilities (latest edition)

National Association of City Transportation Officials (NACTO) Urban Street Design Guide (latest edition)

Institute of Transportation Practitioners (ITE) Designing Walkable Urban Thoroughfares: A Context Sensitive Approach (latest edition)

1.3 Navigating the Guide Utilizing the table of contents at the beginning of the document, users can quickly find topical information that is pertinent to their immediate planning or design need. The following words are intended to be helpful to understand how to apply the guidance and requirements mentioned in the Guide:  Shall: a mandatory condition or action  Should: the standard under normal conditions Rev 3.0 1. Introduction 4/25/19 Page 1-2 Pedestrian and Streetscape Guide

 May: a permissive condition where no requirement for design, application, or standards is intended

1.3.1 Application of Design Features Given the complexities of streetscape design, an evaluation process and engineering judgment are recommended to confirm the implementation of safety treatments or countermeasures is appropriately placed within its context. More than one countermeasure is often needed to provide the most effective solution for pedestrian safety at a given location. In these cases, a more in-depth and site-specific evaluation is needed by an experienced practitioner to determine the combination of countermeasures that provide the maximum safety benefit for the pedestrian. To assist practitioners, speed limit icons are used throughout the Guide to indicate the conditions under which countermeasures and design features are most appropriate. An icon is not provided if a countermeasure or design feature may be used on roads with any speed limit. In addition, a no-truck icon is included in certain sections to indicate design features that may not be appropriate on roads with high volumes of truck traffic. The icons are shown in Figure 1.2.

Figure 1.2. Applicability of Design Features

1.3.2 Benefits of a Streetscape A well-designed streetscape satisfies a variety of mobility needs and interests, and is integral to the larger system of social, economic, environmental, and health considerations for Georgia communities. These considerations serve as the basis for the planning, design, engineering, and implementation processes, enhancing the quality of life of Georgia’s pedestrians while positively

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impacting environmental and economics within an area. A streetscape project is typically designed and implemented in an urban context whether it is a small town or large city. A streetscape project typically involves ADA pedestrian facility upgrades, sidewalk construction, and amenities such as street trees, pedestrian-scale lighting, and an amenity zone for benches, litter receptacles, bike racks, and additional buffered landscape areas. To this point FHWA states, “No single design feature can ensure that a streetscape will be attractive to pedestrians. Rather, the best places for walking combine many design elements to create streets that are comfortable to people on foot. Street trees, separation from traffic, seating areas, pavement design, lighting, and many other factors should be considered in locations where pedestrian travel is accommodated and encouraged.” Above all, the primary goal of a streetscape project is to improve pedestrian safety. Some primary benefits of well-designed streetscapes are described below:

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GDOT Project Delivery - Contents

GDOT Project Delivery - Contents ...... 2-i 2.1 Plan Development Process and Plan Presentation Guide ...... 2-1 2.2 Design Variances and Exceptions ...... 2-3

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GDOT Project Delivery

To improve quality and consistency in the design review process, GDOT has adopted a process for developing construction plans and approving design variances. The standard GDOT process involves quality review checks throughout all stages of a transportation or streetscape project. These checks are intended to improve design-related coordination, develop the construction supplemental agreements, and reduce technical problems, utility delays, and liability claims during construction. This chapter provides an overview of GDOT’s standard processes for developing and submitting construction plans and variances.

2.1 Plan Development Process and Plan Presentation Guide GDOT’s Plan Development Process and the Plan Presentation Guide outline a standardized process for delivering federal-, state-, and locally-funded transportation and streetscape projects, and provide guidance on project plan production and computer aided drafting guidelines. The process and guide support efficient project delivery and create consistency across projects with varying funding sources, site characteristics, and requirements. The Plan Development Process should be applied to the following types of projects:  Construction and right-of-way projects prepared by or for GDOT where GDOT is proposed to let the project to construction.  Construction projects that require the purchase of right-of-way.  Construction projects prepared by the Office of Maintenance requiring full-size plans.  Intelligent transportation system projects.  Major construction projects prepared by or for the Office of Local Grants as set forth in project management agreements.  Projects required by project framework agreements (see GDOT Plan Development Process).  Locally-sponsored projects on the state highway system, interstate system, or where GDOT will be responsible for maintenance. The GDOT Plan Development Process applies primarily to projects on state-owned facilities. Projects on local streets are not required to follow the standard Plan Development Process. GDOT has developed a process for state-funded projects that includes the same major steps as the federal process but provides significant flexibility in the timing of individual steps, with the objective of shortening project delivery. These timelines are illustrated in Figure 2.1. In addition to the timelines, another difference between the federal and state processes is the environmental evaluation and approval as it relates to right-of-way acquisition. Federally-funded projects follow the National Environmental Policy Act (NEPA), whereas state-funded projects follow the Georgia Environmental Policy Act (GEPA). GEPA submittals should be in accordance with GDOT’s Environmental Procedures Manual. Most streetscape and pedestrian upgrade projects fall within a Categorical Exclusion level of environmental approval. Categorical Exclusions are considered to have the least amount of impact on environmental resources.

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Source: GDOT Plan Development Process (2017)

Figure 2.1. Federal and State Plan Development Process Timelines For additional guidance on sub-tasks and certification requirements within each step of state- and federal-process timelines, refer to GDOT’s Plan Development Process, State Funded Projects. When following the Plan Development Process for both federal- and state-funded projects, public participation should be maintained throughout the project so that state and federal funds are not jeopardized. For more information on public involvement refer to Chapter 3 of this Guide and GDOT’s Context Sensitive Design Online Manual.

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2.2 Design Variances and Exceptions When a transportation construction or reconstruction project is located within an “on system” facility, which are roadway facilities owned by the State or a transportation facility owned by the National Highway System, contains design features that do not meet GDOT policy, a design variance should be requested through a formal Design Variance request in writing to the attention of the Chief Engineer. Table 2-1 system conditions that require a design variance approval by GDOT. Additionally, whenever a road construction project on a state route contains design features that do not meet AASHTO guidelines, a design exception should be requested from the Chief Engineer and FHWA for Project Division Interest. If a design variance is anticipated, designers should coordinate with GDOT at an early stage of the project, such as the concept phase. Requests should be listed and identified in the Concept Report for review by GDOT. Design variance and exception templates can be found in the current edition of the GDOT Plan Development Process.

Table 2-1. Facilities that Require a Design Variance

Project Funding/Maintenance On/Off System Variance Required Category I GDOT On System Yes Category II GDOT + Local On System Yes Category III Local Off System No Variance Required

As stated in the Georgia Code § 50-21-24, Exceptions to state liability. “GDOT has decided to waive the requirement of a formal Design Exception or Design Variance for projects on off-system roadways regardless of whether state or federal funding is involved, with the two exceptions listed below: 1. Whenever employees of the Department are directly involved in the engineering and design, right-of-way acquisition, and/or construction letting of a project on an off-system roadway, then the normal approval of a Design Variance by the Department’s Chief Engineer will be required before any deviation to minimum design standards can be incorporated into the project. This also applies to any of the above work activity being accomplished on behalf of the Department by consulting engineering firms or contractors hired by the Department. Design Variances for “Off-System” Projects 1. Any deviation proposed to “Design Loading Structural Capacity” standards will require the normal approval of a Design Variance from the Department’s State Bridge Engineer and/or the Department’s Chief Engineer before any deviation can be incorporated into a project. This change is intended to provide more flexibility to local governments and their Engineer-of-Record, to make practical design decisions for “off-system” roadways within their jurisdiction.” The following are two examples associated with pedestrian infrastructure or streetscape projects located “On System,” which would require a Design Variance approval.  Request to reduce the lateral offset for a fixed object such as a tree or a street light.  Request to reduce the width of a sidewalk.

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Please see 2.2.3 Design Variances for Off-System Roadways, GDOT Design Policy Manual (latest edition) for further guidance.

Further Guidance

GDOT, Context Sensitive Design Online Manual (latest edition) GDOT, Environmental Procedures Manual (latest edition) GDOT, Local Administered Project (LAP) Manual (latest edition) GDOT, Plan Development Process (latest edition) GDOT, Plan Presentation Guide (latest edition) GDOT, Public Involvement Plan for NEPA Projects (latest edition) GDOT, R.O.A.D.S (latest edition) GDOT, Regulations for Driveway & Encroachment Control (latest edition) GDOT, Design Policy Manual (latest edition)

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Planning Streets for Pedestrians - Contents

Planning Streets for Pedestrians - Contents ...... 3-i 3.1 Prioritizing Presentation Safety ...... 3-1 3.1.1 Georgia Complete Streets Policy ...... 3-2 3.1.2 Public Right-of-Way Accessibility Guidelines (PROWAG) ...... 3-2 3.1.3 Georgia Pedestrian Safety Action Plan ...... 3-2 3.1.4 Georgia’s Policy of “Promoting Zero Pedestrian Deaths “ ...... 3-2 3.2 GDOT Complete Streets Policy...... 3-3 3.3 Connected Pedestrian Networks ...... 3-4 3.4 Pedestrian-Oriented Data Collection ...... 3-5 3.4.1 Compile Transportation and Site Development Plans ...... 3-6 3.4.2 Document Existing Infrastructure and Developments ...... 3-6 3.4.3 Observe Pedestrian Activity ...... 3-7 3.5 Context-Sensitive Design for Pedestrian Facilities ...... 3-8 3.5.1 Tactics for Involving the Community ...... 3-9 3.5.1.1 Road Safety Walk Audit ...... 3-9 3.5.1.2 Pop-Up Events...... 3-10 3.5.1.3 Workshops ...... 3-11 3.5.1.4 Advisory Committees ...... 3-11 3.5.2 Street Types and Adjacent Land Uses ...... 3-11 3.5.2.1 Urban Core ...... 3-12 3.5.2.2 Urban ...... 3-14 3.5.2.3 Suburban ...... 3-16 3.5.2.4 Rural ...... 3-17 3.5.2.5 Rural Town ...... 3-18

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Planning Streets for Pedestrians

To create safe, comfortable, and connected spaces for people, designers should consider the needs of pedestrians at the onset of a transportation project. This chapter provides guidance on how to plan for pedestrians in the concept development phase of a transportation project. The concept development phase considers how the project fits into surrounding multimodal networks and studies how the surrounding land uses influence pedestrian activity. This chapter is intended to be used for small- scale corridor level planning. It does not provide exhaustive guidance on creating Figure 3.1. Raised Crosswalk with RRFBs, Atlanta, pedestrian-focused transportation plans and Georgia policies and does not reflect GDOT’s pedestrian infrastructure investment plans. For more information on creating local and regional pedestrian and bicycle master plans, refer to the Atlanta Regional Commission (ARC) bicycle and pedestrian plan, Walk. Bike. Thrive! For more information on pedestrian infrastructure investment needs, refer to the GDOT Statewide Strategic Transportation Plan. For a procedure for planning uncontrolled intersections (mid-block crosswalks), refer to Appendix A for more detailed information.

3.1 Prioritizing Presentation Safety Pedestrian safety is a city or community’s key metric in measuring livability. Providing safe pedestrian facilities and complete networks promotes social and physical health and wellness for all. In recent years, pedestrian injuries and deaths have increased in Georgia. In 2017, 258 pedestrian fatalities were recorded, representing an increase of 91 fatalities from those recorded in 2012. This trend, illustrated in Figure 3.2, can only be reversed by instituting policies, action plans, and roadway design practices that prioritize pedestrian safety. The four most prominent national and statewide pedestrian safety commitments include the GDOT Complete Figure 3.2. Crash History and Goal for Streets Policy, PROWAG, GDOT’s Georgia Reduction in Statewide Pedestrian Pedestrian Safety Action Plan 2018-2022, and Fatalities, 2012–2022

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the Governor’s Office of Highway Safety’s “What GA Codes Say About Pedestrians.” Together, these policies and plans guide the design of pedestrian infrastructure and the development of a connected pedestrian network.

3.1.1 Georgia Complete Streets Policy In 2012, GDOT adopted a Complete Streets Policy that requires pedestrian, bicycle, and transit accommodations to be incorporated into transportation infrastructure projects on a regular basis. The policy establishes standards for where pedestrian infrastructure should be provided. For more information on the Complete Streets Policy, refer to Section 3.2 of this Guide.

3.1.2 Public Right-of-Way Accessibility Guidelines (PROWAG) Roads and streets that are required to accommodate pedestrians should be accessible by people of all ages and abilities. GDOT accepts the PROWAG as the basis for the design of pedestrian infrastructure, except for situations where the FHWA Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD) or AASHTO Green Book does not specifically endorse PROWAG. The conditions under which an exception may be granted are when the PROWAG requirement is structurally impractical, technically infeasible, or unsafe. In those cases, a decision to select a value or retain an existing condition that does not meet the criteria defined in PROWAG should require a comprehensive engineering study and the prior approval of a design variance from the GDOT Chief Engineer. Refer to the GDOT Design Policy Manual Section 9.5 for further information.

3.1.3 Georgia Pedestrian Safety Action Plan The GDOT Georgia Pedestrian Safety Action Plan 2018-2022 outlines strategies and actions that state and local agencies should take to improve pedestrian safety and reduce pedestrian fatalities. The Pedestrian Safety Action Plan identifies locations, corridors, and recurring road characteristics associated with pedestrian crashes throughout Georgia. The plan highlights focus counties, cities , and corridors where pedestrian infrastructure should be improved. When planning and prioritizing infrastructure improvements, local agencies should reference the list of focus destinations in the Pedestrian Safety Action Plan to ensure resources align with the greatest investment need.

3.1.4 Georgia’s Policy of “Promoting Zero Pedestrian Deaths “ The Governor’s Office of Highway Safety states that “Georgia will take decisive and sustained action Towards Zero Deaths – a state with zero pedestrian fatalities and zero serious injuries caused by vehicle-pedestrian crashes.” This statewide commitment fundamentally changes the way state and local agencies in Georgia approach road design and traffic operations. Instead of designing with the assumption that drivers and pedestrians will conform and demonstrate ideal human behavior, the design of infrastructure should account for realistic human behavior. For more information on Georgia’s policy, refer to the Governor’s Office of Highway Safety Georgia Strategic Highway Safety Plan.

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3.2 GDOT Complete Streets Policy The GDOT Complete Streets Policy establishes standards and guidelines for incorporating bicycle, pedestrian, and transit accommodations into transportation infrastructure projects. GDOT’s Complete Streets Policy should be reviewed at the beginning of the concept development phase of a transportation project or planning study on GDOT-owned facilities to determine whether pedestrian infrastructure should be considered. Streets under the jurisdiction of a local agency should also be considered for pedestrian accommodations. Table 3-1 presents questions that break down GDOT’s Complete Streets Policy by warrant. This table can be used as a tool to check whether pedestrian accommodations are warranted on GDOT-owned facilities. The table is intended help practitioners interpret the warrants; however, the final determination should still be made in the context of the warrants. Table 3 1. GDOT Complete Streets Policy: Pedestrian Warrants Policy Check

Questions Y/N Standard Is the project If located in an urban area, is the project a planning study, located in an urban reconstruction, new construction, capacity-adding, or area? resurfacing project which include curb and gutter as part of an urban border area? (Refer to Section 6.7 of the GDOT Design Policy Manual for more information on urban border areas). Is the project If located in a rural area, are there existing or planned located in a rural pedestrian travel generators and destinations along the area? segment of roadway under evaluation? (Generators and destinations can include but are not limited to residential neighborhoods, commercial areas, schools, public park, transit stops and stations, and convenient stores). If located in a rural area, is there evidence of pedestrian traffic (e.g., a worn path along roadside) at any point along the segments of roadway under evaluation? If located in a rural area, have there been pedestrian crashes equal to or exceeding the rate of 10 crashes per ½ mile segment of roadway over the most recent five years for which crash data is available? If located in a rural, has a local or regional adopted planning study identified the need for pedestrian accommodations for any point along the segment of roadway under evaluation? Guidelines Is there a school, college, university, major institution, shopping center , convenience store, park, or another major pedestrian generator along or within close proximity to the segment of roadway under evaluation? Is there a shared use path or transit stop along the segment of roadway under evaluation? Is there an approved development that may generate pedestrian traffic in the future within close proximity to the segment of roadway under evaluation? Is the project in an urbanized area or an area projected to be urbanized by an MPO, regional commission, or local government prior to the design year of the project?

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Questions Y/N Have one or more pedestrian fatalities occurred along the segment of roadway under evaluation? Has a vehicle-pedestrian crash occurred in the past five years along the segment of roadway under evaluation? Do any city, county, MPO, or regional commission plans (comprehensive transportation plans, livable community, community development plans, etc.) identify the need for pedestrian accommodations along the segment of roadway under evaluation? Has reasonable community interest related to pedestrian infrastructure been received in the past two to four years?

Steps after reviewing the policy:  If one or more of the standard warrants are met for streets under GDOT’s jurisdiction, pedestrian accommodations should be incorporated into the infrastructure project.  If one or more of the standard warrants are met and the accommodations are impractical, technically infeasible, or unsafe, a design variance and coordination with the district traffic operations office are required. Refer to Section 9.4 of the GDOT Design Policy Manual for more information on obtaining a design variance.  If the standard warrants are not met but one or more of the guideline warrants are met for streets under GDOT’s jurisdiction, pedestrian accommodations should be incorporated into the infrastructure project.

3.3 Connected Pedestrian Networks Maintaining and improving the connectivity and usefulness of the overall pedestrian network in the project area should be a key focus throughout the planning and design process. A well-connected pedestrian infrastructure promotes walkability as destinations can be obtained through a safe and efficient pedestrian network. During the planning process, attention should be paid to how a project location fits into the surrounding pedestrian, transit, and bicycle networks (including planned facilities). Designers should assess where pedestrian travel demand exists or may exist in the future and how well that demand is already being served. The GDOT Complete Streets Warrants provide a good starting point for identifying Figure 3.3. School Crossing, Decatur, Georgia the presence of pedestrian trip generators in the area; however, it is necessary to go a step further and consider how they fit together and how a

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project can be designed to promote pedestrian mobility and safety between the destinations in the area. Once walkable destinations have been identified, the next step is to connect these places through safe, efficient pedestrian infrastructure that is responsive to the needs of the users. When planning and designing connections, it is important to pay close attention to the proximity of destinations, observe where people are walking today, and consider how new development might generate more pedestrian activity and introduce new travel paths. Knowing where people want to walk will help to prioritize investments and identify where pedestrian infrastructure should be implemented, such as crosswalks, midblock crossings, curb extensions, pinch points, traffic calming features, etc. Practitioners should collect, and document data related to the pedestrian network in the early stages of a project. Section 3.4 provides recommendations for what type of data should be collected to support a thorough assessment of pedestrian needs in a project area.

3.4 Pedestrian-Oriented Data Collection During the initial planning phase of a roadway project, it is common practice for practitioners to collect data on existing traffic conditions, roadway characteristics, and crash history in the project study area. These site assessments should also study and document existing and future pedestrian activity and adjacent developments. This section can be used to help guide the practitioner in capturing useful pedestrian-oriented data during the site assessment. The data outlined in this section may be collected for the following types of roadway projects: Figure 3.4. Road Safety Walk Audit  Road construction and reconstruction  3R (resurfacing, restoration, rehabilitation) projects  Corridor or intersection restriping  Targeted safety improvements  Road safety audits  Traffic engineering studies  Streetscape projects  Corridor planning project

Figure 3.5. Streetscape, Midtown, Atlanta, Georgia

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3.4.1 Compile Transportation and Site Development Plans Background information from transportation or community development plans related to the site will help identify previous discussions, assumptions, and decisions made related to pedestrian infrastructure. Proposed and approved site development plans will provide insight into where future pedestrian activity is likely to occur. Together, these documents will help evaluators understand the history, provide direction for future modifications (if any), and support the final recommendation. At the onset of a project, designers should ask the following questions:  Do previously adopted plans and/or concept design documents mention the need for or provide recommendations for pedestrian infrastructure in the study area?  How much pedestrian activity will future developments generate?

3.4.2 Document Existing Infrastructure and Developments Existing roadway configuration, pedestrian accommodations, and adjacent land uses, and developments should be used to determine the type and location of pedestrian infrastructure. Existing conditions and proposed developments should be evaluated so that the pedestrian facilities or countermeasures can be designed or phased to accommodate the future conditions. In addition, existing historic districts, features, landmarks, and environmentally sensitive areas should be identified early on to avoid or minimize any impacts to these features. When assessing existing site conditions, consider the following questions:  What are the adjacent existing and future land uses or developments (i.e., multi-family housing, grocery store, educational institution, etc.)?  What are the existing and proposed densities of these adjacent land uses?  What are the existing pedestrian accommodations (i.e., shared use path, sidewalk, and worn foot paths in the dirt)?  Where are the existing pedestrian accommodations along street segments (both sides of the street, one-side)?

 What are the existing pedestrian Figure 3.6. Example of Mixed-Use accommodations at intersection and mid- Development, Smyrna, Georgia block crosswalks (marked crosswalks or unmarked crosswalks, traffic circles, curb extensions, crossing islands, etc.)?  What is the existing roadway configuration including the width of roadway (from curb to curb), number of lanes, turn lanes, presence and type of bicycle infrastructure, parking lanes, and the presence of painted or raised medians or traffic calming features?  What is the type (painted, raised, planted, etc.) and dimensions of the median (if applicable)?  Are physical barriers present either along the roadway or leading up to the roadway that are channelizing pedestrians to certain crossing points (fences, ditches, vegetation, etc.)? Rev 3.0 3. Planning Streets for Pedestrians 4/25/19 Page 3-6 Pedestrian and Streetscape Guide

 Are there traffic controls (stop signs, traffic signals, marked crosswalks, rectangular rapid flashing beacons [RRFB], pedestrian hybrid beacons [PHB], warning signs, etc.) along the corridor?  If there is a traffic signal along the corridor, how long is the pedestrian signal phase? Are there special features such as a pedestrian scramble or leading pedestrian interval?  If there is a marked crosswalk, what is the pedestrian crossing sight distance at the crosswalk?  Are there lights along the corridor? If so, what is their primary function (i.e., Pedestrian or Roadway lighting)? Or do both complement each other providing safe conditions for all users.  Where are the transit (bus or train) stops along the corridor?  Are the transit services high-capacity/frequent transit or lower capacity transit service?  Are there shared use path entrances along the corridor?  Are special events (sports games, farmers markets, concerts, etc.) held on adjacent properties along the corridor?

3.4.3 Observe Pedestrian Activity In order to design useful pedestrian infrastructure, a practitioner should have an understanding of the level and type of pedestrian activity along a corridor. This information can be used to identify the infrastructure, traffic operations, and places to install pedestrian crossings. When collecting traffic data, consider the following questions:  Where are pedestrians walking and crossing the street?  Are pedestrian crossings at intersections or mid-block?  When are the peak hours of pedestrian activity (weekends, lunch time, at night, etc.)?  What are the pedestrian volumes during the Figure 3.7. Peachtree Road, Atlanta, peak hours of pedestrian use along the Georgia segment of street or roadway? Peak hours of pedestrian use typically occur during fair weather conditions and could be different than peak hours of vehicular use. The developments and recurring community events in the study area may serve as indicators to determine the best time to collect data. For example, in some scenarios, pedestrian activity may be elevated on weekends or at night, if there are places of worship or restaurants in the study area. Multiple days of data collection may be necessary to observe peak pedestrian volumes. Three days of data collection is recommended but this may be shortened to one day if sufficient data are obtained based on engineering judgment. It is recommended to count pedestrians separately from bicyclists and to take note of the percentage of pedestrians who are under the age of 16, elderly, or disabled. Other questions to consider include the following:

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 What is the pedestrian compliance rate (i.e., are pedestrians crossing at a marked pedestrian crossing or during a designated pedestrian phase)?  What is the driver compliance rate (i.e., are drivers yielding to pedestrians crossing or waiting the cross the street at a marked crosswalk)?  Are drivers frequently exceeding the speed limit?

3.5 Context-Sensitive Design for Pedestrian Facilities Context-sensitive design is a process of research and public engagement that identifies opportunities and concerns as well as existing context within a project area that is unique. Considerations should be made to preserve the existing identified context and use the context as inspiration for design elements within the streetscape or roadway project. Pedestrian needs are different for every project, as are the surrounding natural and built environments. Thus, a context-sensitive design approach should be employed when planning and designing pedestrian facilities. A context-sensitive approach balances technical analyses with public input and considers the needs of people who live near the corridor, as well as those who use the corridor to pass through an area. For example, residents who live near a corridor may need frequent crossing opportunities, whereas freight companies and drivers commuting to work may desire a high-speed road with few stopping points. Both needs should be considered and accounted for in the planning and design process.

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To achieve a context-sensitive outcome, designers and planners should involve the people who live, own property, and/or operate a business along the street in the early stages of a project and keep them engaged throughout the concept development process. This section provides recommendations on how to involve the community in the planning and design process and describes the different contexts that a roadway may transect. Refer to the GDOT Context Sensitive Design Online Manual for a complete list of context-sensitive solution guiding principles.

3.5.1 Tactics for Involving the Community Figure 3.8. Context Sensitive Brick Pavers, Historic Oakland Cemetery, A key component of the context-sensitive design Atlanta, Georgia approach is continual public involvement throughout the planning and concept development processes. Public involvement is critical to ensure that planning and design decisions reflect local needs and preferences. Each project and community are unique, so a variety of outreach techniques should be employed to connect with and hear from a diversity of stakeholders. The follow subsections describe community outreach strategies that can be used to engage the public and get feedback on the design of pedestrian infrastructure. To best reach all participants within a community or project area, the planning/design team should consult with their client and conduct research to determine the most Figure 3.9. Public Involvement, Atlanta, convenient and efficient way to reach all Georgia stakeholders and citizens as each project context can be different with regards to demographics and access to meetings and online surveys. In many cases, it is best to use a multi-prong approach that provides several options to reach a diverse range of demographics. 3.5.1.1 Road Safety Walk Audit Road safety walk audits are used to inventory the existing walking conditions along a road. Road safety walk audits are opportunities for practitioners, business owners, and community members to visit a site together and identify high-priority safety issues related to the existing pedestrian infrastructure. For more information on how to conduct a road safety walk audit, refer to the FHWA Pedestrian Road Safety Audit Guidelines and Prompt Lists.

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3.5.1.2 Pop-Up Events Pop-up events are casual opportunities for collecting public input and sharing information related to a project. There are two main purposes for a pop-up event:  To bring community members together to realize the temporary transformation of a street into a more pedestrian- or bike-friendly public space and  To test out solutions for bike, pedestrian facilities, and public spaces at popular and easily accessible destinations in a project area. Both types of events can be fun and can generate enthusiasm or momentum for pedestrian-oriented improvements. Pop-up events can also be held in conjunction with larger community events such as Streets Alive, the Georgia Walks Summit, neighborhood festivals, and farmers markets. Hosting pop- up events in conjunction with larger popular community events enables a larger and more diverse group of people to be involved and provide feedback on a project. Participants should always coordinate with and get approval from the local municipalities prior to engaging in the event.

Figure 3.10. Pop-Up Events Figure 3.11. Workshop

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3.5.1.3 Workshops Workshops are interactive events where community members and designers collaborate and brainstorm alternative designs. These events help develop concept design plans that reflect community desires by creating an open and transparent process involving decision-makers, stakeholders, and the public. Types of workshops include:  Educational and information sharing: These workshops focus on informing the public or practitioners about best practices, technical analysis methodology, and the project delivery process.  Design charrettes: Design charrettes are intensive, often multi-day workshops that focus on collecting information and processing it into early concept designs that can be vetted and refined as the project progresses.  Collaborative brainstorming events: These workshops can involve small groups to entire communities. The focus is to solicit ideas from participants for assistance in solving key project Figure 3.12. Pop-Up Events issues.  Walkshops: Similar to road safety audits, these workshops take place in the field and involve walking along the corridor under evaluation. However, they are less formal events that can be used to brainstorm ideas and build community support. 3.5.1.4 Advisory Committees Community advisory committees help formalize an inclusive planning and design process. Advisory committees provide input at milestones in the project and can help gain support and coordination among various groups. These committees are comprised of a diverse cross section of key individuals and organizations that have a vested interest in the project area and outcomes of the project itself. Representatives may include educational professionals, members with disabilities, advocates, residents, business owners, elected officials, and employees of local agencies such as planners, practitioners, law enforcement, public works, and first responders. Extra effort should be made to reach the disabled community or other underrepresented communities to obtain input and representation for their concerns and needs as they are particularly impacted by streets and roads with insufficient pedestrian accommodations. If the project area is within an area with a high concentration of a community whose primary language is not English, additional considerations should be made to have a project team member who can speak the community’s primary language.

3.5.2 Street Types and Adjacent Land Uses The existing and proposed contexts of an area are important when determining proposed transportation improvements. Careful attention should be made in evaluating the existing and future land uses and development trends so that the transportation infrastructure is sized correctly for the

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area. By conducting this evaluation, community leaders, planning/design teams, and citizens can determine the appropriate transportation improvement for the area. In general, a road/street should change in response to the surrounding context, whether it is rural farm land, small towns, suburbs, or urban areas. The design of pedestrian facilities and streetscapes should consider adjacent existing and proposed land uses and existing and projected pedestrian activity along the corridor. The context, or land use transect, generalizes development patterns into five land use contexts that transportation practitioners may commonly encounter in their projects, and their implications for pedestrian infrastructure (Figure 3.13). While the five transects cannot comprehensively capture all land use scenarios, typically many kinds of developments may occur within a project area. For these site-specific developments, additional consideration should be given as to how the development traditionally has interfaced with pedestrian mobility and safety and how to mitigate the challenges often encountered. See Figure 3.16 for an industrial park with high truck volumes and large turning radii. Consideration should be given to increasing offsets from the edge of pavement or travel lane for fixed objects, including pedestrian facilities. Similarly, a low speed residential local street with street trees should be spaced to accommodate light spacing for the street light photo metrics. Traditionally, the functional classifications of streets—using designations such as arterial, collector, and local—have been used to determine appropriate designs for both vehicle and pedestrian facilities. While these classifications are helpful for assessing traffic conditions and determining the appropriate facility design for vehicles, they do not specifically account for pedestrian needs, nor do they provide a framework for assessing the design of pedestrian infrastructure. Alternatively, the context sensitive design approach considers the character of the surrounding area and the corresponding pedestrian activity—in addition to traffic conditions—when designing street infrastructure.

Figure 3.13. Land Use Transects

3.5.2.1 Urban Core The urban core is the densest context and includes a variety of land uses, such as retail, office, and multi-family residential. The urban core context has defined city blocks, minimal building setbacks or build-to requirements, and compact development patterns. These characteristics lend themselves to short travel distances, which can encourage people to walk instead of drive. In addition, traffic congestion and limited parking options naturally make walking,

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biking, and transit the preferred transportation modes in an urban core. To support walking and biking, roads and streets that transect an urban core should be designed to slow vehicular traffic and prioritize pedestrian access. Pedestrian infrastructure along the roads and streets should be designed to accommodate large volumes of pedestrians. In addition, traffic signals should be programed to automatically provide the WALK indication.

Typical Treatments

 Corner Extensions  Pedestrian Refuge Areas  Sidewalks  Crosswalks  Pedestrian-Scale Lighting  Site Amenities such as liter receptacles, benches,  Curb Ramps  Pinch Points planters, wayfinding  Cycle Tracks  Raised Crosswalks signage, etc.  Green Infrastructure  Rectangular Rapid  Street Trees Flashing Beacons  Leading Pedestrian Interval  Transit Stop Amenities  Short Cycle Lengths  On-Street Parking

Figure 3.14. Urban Core Context Area

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3.5.2.2 Urban The urban context is densely developed and includes a variety of land uses, similar to the urban core context but with a reduced scale of development. Minimal building setbacks or build-to standards may be required in some areas. The urban context offers multiple amenities and destinations, and a variety of mobility choices (e.g., walking, biking, transit, and personal vehicles). Shorter travel distances between destinations and the proximity of signalized crossings may encourage walking and biking. While parking is available, it is limited to on-street parking and surface lots and structures that may not be near desired destinations; therefore, people may prefer walking and biking. The urban context may exist adjacent to the urban core or as a node of compact development surrounded by the suburban context. The urban context should balance pedestrian and bicycle activity with vehicle-based travel. Traffic signal control and vehicle speeds should be managed to provide an environment where non- motorized activity is not threatened by vehicle speeds. Pedestrian street crossings may be dense, since the demand for pedestrian crossing is high. Traffic congestion and limited parking are necessary to prioritize the convenience and efficiency of the walkable environment. In addition, traffic signals should be programed to automatically provide the WALK indication.

 Corner Extensions  Pedestrian Refuge Areas  Sidewalks  Crosswalks  Pedestrian-Scale Lighting  Signal Progression  Curb Ramps  Raised Crosswalks  Site Amenities such as liter receptacles, benches,  Cycle Tracks  Raised Intersections planters, wayfinding  Green Infrastructure  Rectangular Rapid signage, etc. Flashing Beacons  Leading Pedestrian Interval  Speed Cushions  Roundabouts  On-Street Parking  Street Trees  Short Cycle Lengths  Pedestrian Recall  Transit Stop Amenities

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Figure 3.15. Urban Context Area

Figure 3.16. Urban Industrial Park Land Use Example

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3.5.2.3 Suburban The suburban context includes a variety of land use types (e.g., residential, commercial, retail, and office) that are rarely mixed with one another on a single site but are connected by a network of arterial and collector streets. Commercial and industrial development is spread out on medium-to-large parcels with greater minimum setbacks and large surface parking lots. Suburban transportation corridors prioritize vehicular mobility from suburban areas to denser areas with employment, service, and entertainment destinations. Biking and walking opportunities may be available through limited on-street and adjacent-to-street facilities (e.g., sidewalks and bike lanes) and the development of off-street trails; however, non-motorized connectivity may be limited due to increased distances between signalized intersections along arterial and collector streets, and the curb cuts and driveways encountered in the suburban context. The suburban context balances the vehicle-based mode and the non-motorized mode. As vehicle speeds become higher, non-motorized facilities must include greater buffer distances from vehicle lanes, and pedestrian street crossings must be designed to optimize pedestrian accessibility and visibility to the driver. Pedestrian street crossings may include enhanced features and should be selected for locations that improve pedestrian mobility and safety while considering driver expectations with respect to crossing locations and traffic control.

 Crosswalks  Pedestrian-Scale Lighting  Signal Progression  Curb Ramps  Radar Speed Signs  Site Amenities such as liter receptacles, benches, etc.  Green Infrastructure  Roundabouts  Street Trees  Leading Pedestrian Interval  Shared Use Paths  Transit Stop Amenities  Pedestrian Hybrid Beacons  Short Cycle Lengths  Pedestrian Refuge Areas  Sidewalks

Figure 3.17. Suburban Context Area

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3.5.2.4 Rural The rural context is characterized primarily by large parcels used for single-family residential or agricultural purposes that have significant setbacks from roadways. Service-oriented businesses are occasionally found in the rural context, including gas stations, small grocery stores, and agricultural equipment dealerships. Mobility options are limited primarily to vehicles due to long travel distances to amenities and destinations. Rural roadways may have earthen or paved shoulders where walking may occur, but are connected in low-density networks, often having few signalized intersections and low-volume but high-speed motorized vehicular use. The rural context introduces high vehicle speeds. The high vehicle speeds require greater separation between vehicles and non-motorized activity. Where pedestrian volumes are higher, particularly near certain land uses such as residential neighborhoods and schools, more robust pedestrian facilities and street crossing with enhanced crossing features may be needed. Shared use paths with more significant offsets from the travel lane should be considered for accommodating both pedestrians and cyclists. As with all projects, context, speed, geometry, site distances, clear zones, etc., should be evaluated independently.

 Crosswalks  Median/Pedestrian Refuge  Roundabouts Areas  Curb Ramps  Shared Use Paths  Pedestrian Hybrid Beacons  Lane Shifts  Short Cycle Lengths  Radar Speed Signs  Leading Pedestrian  Sidewalks Interval

Figure 3.18. Rural Context Area

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3.5.2.5 Rural Town The rural town context is a node of compact, relatively dense development surrounded by the rural context. This context has a variety of land uses that provide commercial services, government facilities, and public amenities to the surrounding area. Within the rural town context, compact development, low traffic volumes, slow speeds, on-street parking, and sidewalks may allow for enhanced walkability. Due to the surrounding low-density rural context, the rural town may be connected to a less dense road network with fewer signalized intersections and limited sidewalk connectivity outside the immediate rural town context. On-street and surface-lot parking accommodate both local patrons and visitors traveling longer distances to access the services and amenities in the rural town. The rural town context is suitable for pedestrian activity and promotes a “park once and walk” approach for commercial patrons and citizens seeking civic services and facilities. The rural town, urban, and urban core contexts are similar in that traffic speeds should prioritize pedestrian activity over vehicle throughput efficiency.

 Chicanes  Pedestrian Refuge Areas  Short Cycle Lengths  Corner Extensions  Pedestrian-Scale Lighting  Sidewalks  Crosswalks  Pinch Points  Site Amenities such as liter receptacles, benches,  Curb Ramps  Radar Speed Signs planters, wayfinding  Green Infrastructure  Raised Crosswalks signage, etc.  Leading Pedestrian Interval  Rectangular Rapid  Speed Tables Flashing Beacons  On-Street Bike Lanes  Street Trees  Roundabouts  On-Street Parking

Figure 3.19. Rural Town Context Area Rev 3.0 3. Planning Streets for Pedestrians 4/25/19 Page 3-18 Pedestrian and Streetscape Guide

Road and Street Design for Pedestrians - Contents

Road and Street Design for Pedestrians - Contents ...... 4-i 4.1 Vehicle Speeds ...... 4-1 4.1.1 Relationship among Vehicle Speed, Pedestrian Comfort, and Injuries ...... 4-1 4.1.2 Posted, Design, and Target Speed ...... 4-2 4.2 Traffic Calming ...... 4-3 4.2.1 Chicanes ...... 4-5 4.2.2 Curb Extensions ...... 4-7 4.2.3 Lane Shifts ...... 4-9 4.2.4 Pinch Points ...... 4-10 4.2.5 Radar Speed Signs ...... 4-12 4.2.6 Signal Progression ...... 4-13 4.2.7 Speed Cushions ...... 4-14 4.2.8 Speed Bumps ...... 4-15 4.2.9 Speed Tables...... 4-17 4.2.10 Two-Way Streets ...... 4-20 4.3 Optimizing the Cross Section for Pedestrians ...... 4-20 4.3.1 ADA Ramps and Detectable Edges ...... 4-20 4.3.2 Bicycle Facility Infrastructure ...... 4-22 4.3.3 Handrails and Safety Railings ...... 4-26 4.3.4 Fencing for Pedestrian Access Control ...... 4-28 4.3.5 On-Street Parking ...... 4-28 4.3.6 Pedestrian Accommodations along Bridges and Constrained Rights-of-Way ...... 4-31 4.3.7 Raised Medians and Pedestrian Refuge Areas ...... 4-32 4.3.8 Roadway and Lane Diets ...... 4-35 4.3.9 Shared Streets ...... 4-38 4.3.10 Shared Use Paths ...... 4-39 4.3.11 Sidewalks ...... 4-44 4.3.12 Transit Stops...... 4-50 4.4 Intersection Design ...... 4-52 4.4.1 Channelized Right-Turn Lanes ...... 4-53 4.4.2 Corner Extensions ...... 4-56 4.4.3 Corner Radii ...... 4-57 4.4.4 Curb Ramps ...... 4-59 4.4.5 Diverging Diamond Interchanges ...... 4-61 4.4.6 Diverters ...... 4-63 4.4.7 Driveway Crossings ...... 4-66 Rev 3.0 4. Road and Street Design for Pedestrians- Contents 4/25/19 Page 4-i Pedestrian and Streetscape Guide

4.4.8 Marked Crosswalks...... 4-68 4.4.9 Pedestrian Bridges and Underpasses ...... 4-72 4.4.10 Protected Intersections ...... 4-75 4.4.11 Raised Crosswalks ...... 4-77 4.4.12 Raised Intersections ...... 4-79 4.4.13 Roundabouts ...... 4-80 4.4.14 Single-Point Urban Interchanges ...... 4-83 4.4.15 Skewed Intersections ...... 4-84

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Road and Street Design for Pedestrians

Designing roads and streets that are accessible and comfortable places for people requires a holistic approach that goes beyond providing the minimum pedestrian accommodation requirement and considers how vehicle speeds, traffic operations, and multimodal safety relate to the pedestrian experience. This chapter provides guidance on the design of pedestrian facilities, as well as several other roadway elements that are not exclusive to pedestrians but whose design has a direct influence on pedestrian mobility and quality of service. The information in this chapter supplements the GDOT Design Policy Manual and other national design policies by providing additional guidance on designing roads and streets for pedestrians.

4.1 Vehicle Speeds

4.1.1 Relationship among Vehicle Speed, Pedestrian Comfort, and Injuries The faster vehicles are traveling, the more stressful walking is for pedestrians and the more likely a pedestrian- vehicle collision will result in a pedestrian fatality. The ability of a driver to stop in time for a pedestrian crossing the street significantly decreases as the vehicle speed increases. The relationships among vehicle speeds, braking distances, and the likelihood of pedestrian fatalities are shown in Figure 4.1.

Figure 4.1. Relationship between Vehicle Speed and Pedestrian Injury

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 FHWA, Pedestrian Safety Program Strategic Plan, Background Report (latest edition)  GDOT, Georgia Pedestrian Safety Action Plan 2018–2022 (latest edition)  Tefft, Impact Speed and a Pedestrian’s Risk of Severe Injury or Death (latest edition)

4.1.2 Posted, Design, and Target Speed The posted speed limit and roadway geometry (which is influenced by design speed) are two major factors that influence the speed at which motorists choose to drive, which in turn plays an important role in the safety of all road users. A third factor discussed in Section 3.5.2 of this Guide is land use, which sometimes has a direct relationship to posted speed. (e.g., a school speed zone is typically provided in the vicinity of a school facility). The posted speed limit is the maximum speed motorists are legally allowed to travel on a given stretch of road, typically communicated using the familiar black and white “Speed Limit” signs posted along roads and streets across the United States . Posted speed limits are set by state statute or by the governing municipality. Regulations and guidelines for changing posted speed limits are set by MUTCD Section 2B.13; however, the policies and practices of applying these regulations and guidelines can vary from agency to agency. For example, some agencies and municipalities use vehicle operating speeds under free-flow conditions (typically the 85th percentile speed) as the sole input in the speed limit setting process. Reasons for using prevailing speeds as an input in the speed limit setting process include:  To avoid setting speed limits that feel artificially low or arbitrary to drivers due to a perceived mismatch between the posted speed limit and the speed at which it “feels” like someone should be able to drive based on the roadway geometry and other factors  An assumed trust that the average motorist (or 85 percent of motorists) has an accurate perception of the risks associated with their speed selection and makes a rational decision when selecting their travel speed given the roadway geometry and other factors However, using vehicle speeds as the sole input for setting speed limits can neglect the safety needs of other road users and lead to situations in which it is difficult or impossible to lower posted speed limits to address safety issues and community needs. In an effort to prevent this pattern, some agencies and municipalities use methods that take multiple factors into account such as local context, adjacent land uses, crash history, and the presence of other road users besides motorists. To help practitioners include multiple inputs in the speed limit setting process, the FHWA provides access to a planning tool called USLIMITS2, which is a web-based tool designed to help practitioners set reasonable, safe, and consistent speed limits for specific segments of roads. USLIMITS2 is applicable to all types of roads ranging from rural local roads and residential streets to urban freeways. However, the tool is not applicable to school zones or construction zones and does not include site-specific data such as roadway geometry and site distances. USLIMITS2 is a helpful planning tool but should not be relied upon solely in determining the final speed for a segment of road or street.

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Because roadway geometry has a major influence on drivers’ speed selection, it is important to consider how design speed and roadway geometry are related. A roadway’s geometry, which includes things like width, curve radii, corner radii, and clear zone requirements, are the result of engineering decisions based on design standards that are related to the roadway’s design speed. When a roadway is being designed or redesigned, engineers first select a design speed to govern the application of various geometric design standards. For existing roadways, the design speed is often selected from the existing posted speed limit or by measuring vehicle operating speeds, such as the 85th percentile speed. However, using existing posted speed limits or vehicle operating speeds to determine design speed and therefore roadway geometry can result in a cyclical situation slanted toward maintaining or increasing vehicle speeds rather than designing for the needs of all users of the right-of-way. To address speed issues in the design process, national transportation professional organizations such as NACTO and ITE encourage designers to select and use a target speed in their design decisions rather than using the existing posted speed limit or observed speeds. The target speed should be selected based on multiple factors, including adjacent land uses, the active transportation activity levels along the street, and the community’s planning objectives for the corridor or neighborhood. Establishing target speeds as part of design projects enables practitioners to design streets that encourage vehicle operators to drive at slower speeds while avoiding issues associated with changing the speed limit alone. The result is a design better suited for balancing the safety, livability, and mobility needs of all users. At the outset of a project, practitioners should evaluate the current design speed from a pedestrian’s perspective and check with project sponsors about the possibility of lowering the posted speed limit if necessary. Current and future pedestrian activity should be considered when setting speed limits. Refer to MUTCD Section 2B.13 for further guidance on establishing or reevaluating speed limits.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, Achieving Multimodal Networks: Applying Design Flexibility and Reducing Conflicts (latest edition)  ITE, Implementing Context Sensitive Design on Multimodal Corridors: A Practitioner's Handbook (latest edition)  NACTO, Urban Street Design Guide (latest edition)

4.2 Traffic Calming Traffic calming infrastructure reduces vehicle speeds, and in some cases volumes, by introducing horizontal and vertical features that interrupt a straight travel path. Careful consideration should be made in determining the appropriate measure for the appropriate roadway functional classification. Traffic calming measures are specific to the roadway functional classification. Another traffic calming method that can be effective is reducing the travel lane’s width. Some types of traffic calming infrastructure are relatively inexpensive and can be quickly implemented as part of a maintenance or quick-response project. Other types of traffic calming infrastructure can include

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impacts to stormwater management and underground or overhead utilities. While most traffic calming infrastructure is not used by pedestrians, the reduction in vehicle speeds improves the conditions for pedestrians and the overall walkability of a city or community. This section provides information on the applicability and design of traffic calming features. Table 4-1, from the FHWA Traffic Calming ePrimer, shows the applicability and acceptability of individual traffic calming measures within a given roadway functional classification.

Table 4-1. Traffic Calming Measures and Their Appropriate Applications

Street Functional Classification Street Function Local or Traffic Calming Segment or Collector or Thoroughfare Local Emergency Transit Measure Intersection Residential or Major Resident Access Route Collector ial Horizontal Deflection Lateral Shift Segment 3 5 5 5 5 Chicane Segment 1 5 5 3 3 Realigned Intersection 1 5 5 5 5 Intersection Traffic Circle Intersection 1 3 5 3 3 Small Modern & Intersection 3 3 5 5 5 Mini- Roundabout Roundabout Intersection 5 3 1 5 5 Vertical Deflection Speed Hump Segment 1 5 5 1 3 Speed Cushion Segment 1 5 5 5 5 Speed Table Segment 3 5 5 1 3 Offset Speed Table Segment 3 5 5 5 3 Raised Crosswalk Both 3 5 5 1 3 Raised Intersection Intersection 3 5 5 3 3 Street Width Reduction Corner Extension Intersection 5 5 5 5 5 Choker Segment 5 5 5 5 5 Median Island Both 5 5 5 5 5 On-Street Parking Segment 5 5 5 5 5 Road Diet Both 5 5 3 5 5 Routing Restriction Diagonal Diverter Intersection 1 3 3 1 3 Full Closure Both 1 3 3 1 1 Half Closure Intersection 1 5 5 3 3

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Street Functional Classification Street Function Local or Traffic Calming Segment or Collector or Thoroughfare Local Emergency Transit Measure Intersection Residential or Major Resident Access Route Collector ial Median Barrier Intersection 3 5 5 1 3 Forced Turn Island Intersection 3 5 5 3 3 Legend: 5 – traffic calming measure may be appropriate 3 – caution; traffic calming measure could be inappropriate 1 – traffic calming measure is likely inappropriate

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  AASHTO, Guide for the Planning, Design, and Operation of Pedestrian Facilities (latest edition)  FHWA, Traffic Calming ePrimer (latest edition)  ITE, Traffic Calming Fact Sheets (latest edition)  NACTO, Urban Street Design Guide (latest edition)

4.2.1 Chicanes Chicanes are a series of curb extensions or other features, such as edge islands or on-street parking, that alternate from one side of the street to the other. Edge islands are raised spaces that extend into the street and are offset from the curb. These traffic calming features encourage motorists to drive at slower speeds by restricting vehicle acceleration. Chicanes also provide additional space for landscape planting and stormwater management features. Chicanes are appropriate for low speed streets or roads, 35 mph or less, and are often effective traffic calming measures for a residential context.

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Application

 Chicanes are appropriate for streets with a speed limit of 35 mph or less (ITE Traffic Calming Fact Sheets).  Chicanes are appropriate on low-volume streets (maximum 3,500 vehicles per day).

 Chicanes may be installed at mid-block locations along a street.  Chicanes may be used on one-lane, one-way streets and two-lane, two- way streets.  Chicanes may be installed on primary emergency vehicle and bus transit routes, provided traffic volumes are low enough to allow an emergency vehicle to straddle the street centerline. Chicanes can utilize mountable curbs for easier access for emergency vehicles, buses, and delivery and garbage trucks.  Chicanes are not appropriate at pedestrian crossings.

Critical Design Requirements

 The target speed should be used to determine the degree of horizontal deflection for chicanes.  Chicanes should be made visible with signs, painted curbs, reflectors, markings, or street lights to guide motorists. If chicanes interrupt bike lanes, bicyclists should be diverted around the chicane by either (1) transitioning the bike lane into a sharrow or (2) providing a minimum 4- foot-wide space between the sidewalk curb and the extension. Signage should be provided to alert the bicyclist of the change in infrastructure.  Plantings in chicanes should be low-maintenance and low-growing plants, less than 30 inches in height at maturity.

Additional Considerations

 Chicanes may be designed using curb extensions, on-street parking, or edge islands.  Edge islands may be used to maintain existing drainage channels.  Chicanes may be designed as bioretention or biofiltration planters.  A best practice is to provide mountable curbs to assist with accessibility for emergency vehicles, buses, and delivery and garbage trucks.

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Figure 4.2. Plan of Chicanes

4.2.2 Curb Extensions The primary purpose of curb extensions related to pedestrian safety is reducing pedestrian crossing distances at intersections and street crossings. Curb extensions have many benefits, such as providing additional room for streetscape amenities that do not obstruct views and are set back according to the lateral horizontal setback requirements, and protecting vehicles parked on street. They also increase the visibility between pedestrians and motorists at pedestrian crossing locations. Additionally, curb extensions slow vehicles down by narrowing the street and reducing turning radii at intersections. The types of curb extensions vary based on where they are installed and how they are designed. Curb extensions installed at intersections are referred to as corner extensions and can be applied to all four corners of an intersection to reduce pedestrian crossing distances. When installed at mid- block locations, they are commonly referred to as pinch points. When there is a gap between the extension and the curb of the sidewalk, they are referred to as edge islands. A series of curb extensions or edge islands installed in an alternating pattern along both sides of a street is known as a chicane. When a curb extension is installed at a transit stop, it is referred to as a bus bulb-out. This section provides information on the design of curb extensions. Pinch points, chicanes, bulb-outs, and corner extensions are discussed in more detail in Sections 4.2.4, 4.2.1, 4.3.12, and 4.4.2, respectively.

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 Curb extensions can be installed at intersections or mid-block locations. The application of a curb extension varies based on the type of curb extension (e.g., corner extension, pinch point, bus bulb-out).  Curb extensions are better suited on streets with speed limits of 40 mph or less.

 Curb extensions can provide added protection to on-street parking.  Curb extensions are aesthetically helpful to visually break up long stretches of on-street parking.

 Not appropriate for high volume truck routes.

 If the curb extension includes a pedestrian crossing, streetscape amenities (e.g., lighting, signs, benches, bike racks), or landscaping on the curb extension should not obstruct visibility between the pedestrian and vehicles in the travel lanes.  If used for a pedestrian crossing, applicable ADA measures should be implemented.

 Curb extensions may be opportunities to incorporate green stormwater infrastructure (e.g., bioretention planters) into the street. Section 6.4 contains additional guidance related to green infrastructure, which are only allowed on local off system streets.  Curb extensions can provide additional space for streetscape amenities without protruding into the space dedicated for pedestrian access. Section 6.2.3 contains information on the placement of furniture in curb extensions.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  ITE, Implementing Context Sensitive Design on Multimodal Corridors (latest edition)  NACTO, Urban Street Design Guide (latest edition)

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Figure 4.3. Plan View of Curb Extensions

4.2.3 Lane Shifts Lane shifts are horizontal changes in the travel lane alignment. Like chicanes, lane shifts reduce vehicle speeds by forcing vehicles to move laterally back and forth while driving along a street. Whereas chicanes are more appropriate on streets with a speed limit of 35 mph or less, a lane shift can be incorporated into a higher speed roadway as long as specific criteria are met related to MUTCD, Lane Reduction Transition Markings.

 Lane shifts may be used on streets with any speed limit as long as the guidance is met for the particular condition (MUTCD, Lane Reduction Transition Markings).

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 Lane shifts should only be implemented at mid-block locations.  Lane shifts should be designed using the MUTCD taper formula (MUTCD, Lane Reduction Transition Markings).

 While lane shifts can be facilitated by implementing curb extensions or on-street parking, they can also be designed with painted markings.  A STAY IN LANE (R4-9) sign may be used where a multi-lane shift has been implemented.  Highly visible edge lines or reflectors around landscape plantings may be used to guide motorists.  A center island may be used to reduce conflicts between opposing traffic.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, MUTCD, Lane-Reduction Transition Markings  FHWA, Traffic Calming ePrimer (latest edition)  ITE, Traffic Calming Fact Sheets (latest edition)

Figure 4.4. Plan View of a Lane Shift

4.2.4 Pinch Points Pinch points, also known as chokers, are curb extensions applied on both sides of a street, its primary purpose is for traffic calming whereas a curb extension’s primary purpose is to reduce the length of the pedestrian crossing. This traffic calming feature can reduce vehicle speed and provide additional space for landscaping. Pinch points may be installed as continuous extensions of the curb or as edge

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islands. Edge islands are raised spaces that extend into the street and are offset from the curb. When used at marked or unmarked mid-block crossings, pinch points help delineate direct crosswalk paths, shorten the crossing distance, and increase visibility between pedestrians and vehicles in the travel lanes.

 Pinch points may be used streets with a speed limit of 40 mph or less.  Pinch points may be used on one-lane, one-way and two-lane, two-way streets.  Pinch points are not appropriate on high-volume truck routes.

 Pinch points are appropriate along primary emergency vehicle and bus transit routes.  In addition, curb extensions reduce pedestrian crossing distances and increase the visibility between pedestrians and motorists at pedestrian crossing locations.

 If the pinch point is installed at a marked or unmarked pedestrian crossing, street furniture or landscape planting on the curb extension should not obstruct the visibility between pedestrians and vehicles in the travel lanes.  If the pinch point is installed at a marked or unmarked pedestrian crossing, curb ramps should be installed on both sides of the street.  Pinch points should be 6 to 8 feet wide and offset from the through traffic lane by 1.5 feet (ITE Traffic Calming Fact Sheets).  The length of a pinch point, curb extension, or edge island should be at least 20 feet (ITE Traffic Calming Fact Sheets).  If pinch points interrupt bike lanes, bicyclists should be diverted around the pinch point by either (1) transitioning the bike lane into a sharrow (a shared bike and automobile lane) or (2) providing a minimum 4-foot-wide space between the sidewalk curb and the extension. Signage should be provided to alert the bicyclist of the change in infrastructure.

 On a two-way, two-lane roadway, a pinch point can be installed in combination with a median refuge island as a means to increase pedestrian safety when crossing more than one travel lane and may help reduce the possibility of opposing vehicle conflicts.  Pinch points can also be installed using low-cost interim treatments such as bollards, striping, or planters.

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 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, Traffic Calming ePrimer (latest edition)  ITE, Traffic Calming Fact Sheets (latest edition)  NACTO, Urban Street Design Guide (latest edition)

Figure 4.5. Standard Dimensions of a Pinch Point

4.2.5 Radar Speed Signs Radar speed signs are electronic message signs that display to approaching drivers the speed at which they are traveling, and in turn, when they are exceeding the speed limit.

 Radar speed signs may be used on streets with any speed limit.  Radar speed signs may be permanently installed or temporarily deployed at locations where drivers frequently exceed the speed limit.

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 Radar speed signs should be designed in accordance with FHWA MUTCD (latest edition).

 FHWA, MUTCD (latest edition)

4.2.6 Signal Progression Coordinated traffic signals with short cycle lengths regulate vehicle speeds between signals and decrease pedestrian delay. The speed of vehicle travel on a corridor may also be influenced by the offsets programmed for the green light. Refer to Section 5.1 for further guidance on signal timing strategies that can benefit pedestrian circulation.

 Traffic signals in urban core, urban, suburban, and rural town context areas may be coordinated and programed with short cycle lengths.

 ITE, Guidance on Signal Control Strategies for Pedestrians to Improve Walkability (latest edition)  NACTO, Global Street Design Guide (latest edition)

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4.2.7 Speed Cushions Speed cushions are speed humps that include wheel cutouts to enable a vehicle with wide tracks (e.g., emergency vehicles and buses) or a bicycle to pass through the feature without vertical deflection. A speed cushion is often preferred to a speed hump or speed table (see Sections 4.2.8 and 4.2.9) for streets that serve as a primary emergency response or bus route.

 Speed cushions may be used on streets with a speed limit of 40 mph or less  Speed cushions may only be used at mid-block locations.  Speed cushions are appropriate on primary emergency vehicle access and bus routes, but not on routes with high truck volumes.

 Speed cushions are preferred over speed humps and speed tables on bicycle routes.  May not be appropriate on steep grades.

 Speed cushions should be 3 to 4 inches in height and span 12 to 14 feet wide along the vehicle travel path.  The wheel cut-out should be 3 feet wide (perpendicular to the travel path).  The slope length should be from 3 to 6 feet, depending on target speed.  Speed cushions should be placed in a series with a distance ranging from 200 to 500 feet apart to keep the vehicle operating speed between 25 and 30 mph.  If used in a series, the first speed cushion should be installed 200 feet or less from a street corner or stop-controlled intersection, to discourage vehicles from approaching the first speed cushion at a high speed.

 In urban areas with curb and gutter, speed cushions may be placed 1 to 2.5 feet from the curb to maintain stormwater drainage paths.  In rural areas, or areas without curb and gutter, speed cushions may be placed 6 inches from the edge of the roadway to maintain stormwater drainage paths.  Pavement markings and signage for a speed cushion should replicate those for a speed hump (see Section 4.2.8).

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Figure 4.6. Typical Dimensions of Speed Cushions

4.2.8 Speed Bumps Speed humps have an elongated parabolic profile that extends across the travel lanes at a right angle to the roadway. A speed hump may effectively slow vehicles down to a speed potentially less than the posted speed.

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 Speed humps are not appropriate on primary emergency vehicle access and may not be appropriate on bus routes.  Speed humps may be used on streets with speed limits of 25 mph or less.  Speed humps are best utilized at mid-block locations and in residential areas or

school zones where speed reduction is desired.  May not be appropriate on steep grades.

 Speed humps should be 3 to 4 inches in height and span 12 to 14 feet along the vehicle travel path.  The slope length should be 3 to 6 feet, depending on target speed.  If used in a series, the first speed hump should be installed 200 feet or less from a street corner or stop controlled intersection, to discourage vehicles from approaching the first speed hump at a high speed.  In urban areas with curb and gutter, speed humps should be placed 1 to 2.5 feet from the curb to maintain stormwater drainage paths.  In rural areas, or areas without curb and gutter, speed humps should be placed 6 inches from the edge of the roadway to maintain stormwater drainage paths.

 A best practice is to space speed humps 200 to 500 feet apart to keep vehicle operating speed between 25 and 30 mph.  If speed humps are installed along bicycle routes, the curb-side edge of the speed hump can be tapered to allow bicyclists to more safely circumvent the speed hump.

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Figure 4.7. Typical Dimensions of Speed Humps

4.2.9 Speed Tables A speed table has an elongated and extended profile with a flat top. Speed tables are longer than speed humps, allowing both the front and rear wheels of a passenger vehicle to be on top of the table at the same time. Speed tables may be used on streets with higher speeds than a speed hump. In urban areas with curb and gutter, speed tables can be placed 1 to 2.5 feet from the curb to maintain stormwater drainage paths. When used to elevate a pedestrian crossing, special accommodations should be made for stormwater drainage and to allow smooth transitions from the sidewalk curb height to the speed table.

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 Speed tables may be used on streets with a posted speed limit of 45 mph or less.  Where applied, speed tables may be designed as raised midblock crossings, often in conjunction with curb extensions.  Speed tables are generally not appropriate for a primary emergency vehicle route or street that provides access to a hospital or emergency medical services. Another form of vertical deflection – a speed cushion – may be more appropriate.  Speed tables should not be applied on streets wider than 50 feet.  On two-way streets, speed tables may be applied in both directions.  Speed tables are generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more.  ITE Guidelines for the Design and Application of Speed Humps recommends consideration if no more than 5 percent of the overall traffic flow consists of long- wheelbase vehicles.  Generally, not appropriate for a bus transit route with BRT, Express, or Limited Stop service (unless the posted speed limit is 30 mph or less); a speed cushion could be more appropriate.  ITE Guidelines for the Design and Application of Speed Humps recommends consideration only with a grade of 8 percent or less.  Not appropriate along the primary access to an industrial site with require large volumes of truck traffic or designated truck routes.

 Speed tables should be 3 to 4 inches in height.  Slopes should not exceed 1:10 or be less steep than 1:25.  Side slopes on tapers should be no greater than 1:6.  Speed tables should range from 20 to 22 feet along the vehicle travel path (10 feet flat top and two (2) 6-foot ramps on either side).  Speed tables should be placed from 200 to 500 feet apart to keep vehicle operating speed between 25 and 30 mph.  If used in a series, the first speed table should be installed 200 feet or less from a street corner, or stop controlled intersection, to discourage vehicles from approaching the first speed table at a high speed.  Vertical speed control elements should be located where there is sufficient visibility and available lighting.

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 A best management practice is to utilize speed tables to elevate pedestrian crossings. This treatment is referred to as a raised pedestrian crosswalk. The elevated crossing draws attention to the crosswalk and slows vehicles down as they approach the pedestrian crosswalk.  In rural areas or areas without curb and gutter, speed tables may be placed 6 inches from the edge of the roadway to maintain stormwater drainage paths.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  American with Disabilities Act  FHWA, Traffic Calming ePrimer (latest edition)  GDOT, Design Policy Manual (latest edition)  ITE, Traffic Calming Fact Sheets (latest edition)  NACTO, Urban Street Design Guide (latest edition)  NACTO, Urban Street Design Guide (latest edition)

Figure 4.8. Typical Dimensions of Speed Tables

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4.2.10 Two-Way Streets Two-way streets, as opposed to one-way streets, require motorists to be more cautious of oncoming traffic thus influencing them to drive at slower speeds. However, the vehicle speed reduction improves the pedestrian environment, crossing a two-way street is also more difficult and creates greater delay for a pedestrian, since the pedestrian must judge simultaneous gaps in traffic for both directions of travel. When converting a one-way street to a two-way street, curb extensions can be used to reduce the crossing distance for pedestrians. Medians are also important considerations. Medians and pedestrian refuge areas effectively turn two-way streets into two consecutive one-way street crossings for pedestrians. Together, these treatments can be effective in reducing vehicle speeds and simplifying the crossing process for pedestrians. Section 4.3.7 provides further guidance on the design of medians and refuge areas.

Figure 4.9. Plan View of Two-way Street

4.3 Optimizing the Cross Section for Pedestrians As a street traverses places where people are likely to be walking, such as urban, urban core, suburban, rural town, and rural context areas, the design of cross-sectional elements should balance pedestrian mobility, access, and comfort with vehicle operational performance. This section provides information on the design of cross-sectional elements on sections of a street that traverse places where people walk.

4.3.1 ADA Ramps and Detectable Edges To allow people with disabilities to cross streets safely, state and local governments must provide curb ramps at pedestrian crossings and at public transportation stops where walkways intersect a curb. To comply with ADA requirements, the curb ramps provided must meet specific standards for width, slope, cross slope, placement, and other features which shall follow all specifications associated with American Disabilities Act as well as the United States Access Board/PROWAG. GDOT has a regulatory responsibility under Title II of ADA and Section 504 of the Rehabilitation Act of 1973 to ensure that recipients of federal-aid and state and local entities that are responsible for roadways and pedestrian facilities do not discriminate on the basis of disability in any highway transportation program, activity, service, or benefit they provide to the general public. Any GDOT work or project classified as an “alteration” must install, repair, or upgrade curb ramps within the scope of the work or the project. The need to install, repair, or update curb ramps should be discussed

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during the early scoping phase of the work or the project so that budgets and schedules reflect the requirement. Refer to GDOT Construction Detail A-3 and Construction Detail A-4 for design of ADA compliant curb ramps and detectable warning surface/truncated domes. ADA detectable edges are used to communicate to visually impaired pedestrians where a sidewalk crosses a street or commercial driveway.

 Where curbs or a vertical elevation change between the street and sidewalk exists, ADA ramps should be used to allow people with disabilities to cross streets and access sidewalks safely.  ADA ramps should be installed in conjunction with improvements, new alignments, or alterations within the limits of the specific transportation project.  ADA detectable edges are used where the sidewalk or shared use path crosses roads, streets, and railroads.  ADA detectable edges are used where the sidewalk or shared use path crosses commercial driveways with large volumes of entering and exiting vehicles.  ADA detectable edges are not used at crossings of residential driveways.  ADA detectable edges are used in medians - or pedestrian refuge areas with cut-throughs or ADA ramps for pedestrians.  ADA detectable edges are used on boarding platforms at transit stops for buses and rail vehicles where the edge of the boarding platform is not protected by screens or guards.

 Refer to GDOT Construction Detail A-3 and Construction Detail A-4 for the design of ADA- compliant curb ramps and detectable warning surface/truncated domes.  There should be a high visual contrast between the detectable warning and an adjoining surface or the detectable warning should be “safety yellow” (Figure 4.10).

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Figure 4.10. Detectable Pavers – “Safety Yellow”

4.3.2 Bicycle Facility Infrastructure Providing safe spaces for people of all ages to ride bicycles is equally important as providing places for people to walk. Bicycle facilities can be complementary to pedestrians to provide high performance streetscapes. Similar to interconnected pedestrian facilities, bicycle facility planning requires analysis, evaluation, and design to implement facilities that are safe and efficient for people who bike. For each proposed bicycle facility, a specific site evaluation must be conducted to determine the most appropriate facility for the project. Bike lanes are a portion of the roadway designated by striping, signage, and pavement markings for the preferential or exclusive use of bicyclists. Bike lanes enable bicyclists to ride at their preferred speed without interference from prevailing traffic conditions and facilitate predictable behavior and movements between bicyclists and motorists. A bike lane is distinguished from a cycle track in that it has no physical barrier (bollards, medians, raised curbs, etc.) that restricts the encroachment of motorized traffic. Conventional bike lanes run curbside when no parking is present, adjacent to parked cars on the right-hand side of the street or on the left-hand side of the street in specific situations. Bike lanes typically run in the same direction of traffic, though they may be configured in the contra- flow direction on low-traffic corridors necessary for the connectivity of a particular bicycle route. Sharrows are road markings used to indicate a shared lane environment for bicycles and automobiles. Among other benefits, shared lane markings reinforce the legitimacy of bicycle traffic on the street, recommend proper bicyclist positioning, and may be configured to offer directional and wayfinding guidance. The shared lane marking is a pavement marking with a variety of uses to support a complete bikeway network; it is not a facility type and should not be considered a substitute for bike lanes, cycle tracks, or other separation treatments where these types of facilities are otherwise warranted or space permits. MUTCD Section 9C.07 outlines guidance for shared lane markings.

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Two-way cycle tracks (also known as protected bike lanes, separated bikeways, and on-street bike paths) are physically separated cycle tracks that allow bicycle movement in both directions on one side of the road. Two-way cycle tracks share some of the same design characteristics as one-way tracks but may require additional considerations at driveway and side street crossings to provide safe site visibility. A two-way cycle track may be configured as a protected or raised facility. A protected cycle track is located at the same level as the street and includes a parking lane or other barrier between the cycle track and the motor vehicle travel lane. A raised cycle track has vertical separation from the adjacent motor vehicle lane. One-way protected cycle tracks are bikeways that are at street level and use a variety of methods for physical protection from passing traffic. A one-way protected cycle track may be combined with a parking lane or other barrier between the cycle track and the motor vehicle travel lane. When a cycle track is elevated above street level it is called a raised cycle track, and different design considerations may apply.

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 On-street bike lanes may be appropriate on streets with speed limits between 25 mph and less than 40 mph.

 Sharrows or shared lane markings may be appropriate on streets with speed limits of 25 mph or less.

 Buffered cycle tracks are dedicated bicycling facilities that may be appropriate on streets with a speed limit of between 25 mph and 45 mph.

 Cycle tracks should be incorporated in areas with existing or proposed high volumes of cyclists.  Cycle tracks should be maintained in order to be free of potholes , broken glass, and other debris.  Street sweeping maintenance may be required for cycle tracks more frequently than on streets, especially during the fall. The lack of the sweeping effect of motor traffic, together with the canyon profile of a cycle track, tends to hold leaves and other debris.  Bikeable shoulders are appropriate in rural context areas or streets with no curb and gutter. Further evaluation should be conducted related to the posted design speed to determine the most appropriate measures to project the cyclists from motorized vehicles. In many cases, barriers are put up as needed adjacent to the bike facility.

 AASHTO, Guide for the Development of Bicycle Facilities (latest edition)  FHWA, MUTCD (latest edition)  FHWA, Rumble Strips and Stripes (latest edition)  FHWA, Separated Bike Lane Planning and Design Guide (latest edition)  NACTO, Urban Bikeway Design Guide (latest edition)  NACTO, Urban Street Design Guide (latest edition)

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Figure 4.11. Typical Cycle Track Perspective with Tree Grates

Figure 4.12. Two-Way Buffered Cycle Track with Green Infrastructure, Decatur, Georgia

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4.3.3 Handrails and Safety Railings Handrails that are used to assist pedestrians up and down slopes and steps are an essential component of a streetscape where the sidewalk deviates from the roadway slope and requires an ADA accommodation. Safety railings are used to prevent pedestrians from a fall when the sidewalk or landing is adjacent to a vertical drop or slope that requires a barrier.

 Vertical features such as handrails and safety railings are used to assist pedestrians in navigating up and down stairs and ramps, and to prevent pedestrian falls from elevated walkways, platforms, or landings.

 Handrails should extend at least 12 inches beyond the top and bottom of a slope or bottom tread of steps that require a handrail.  Handrails should be 34 inches to 38 inches in height along slopes or steps.  Handrail gripping surfaces with a circular cross section should have an outside diameter of 1¼ inches minimum and 2 inches maximum.  Handrail gripping surfaces and any surfaces adjacent to them should be free of sharp or abrasive elements and should have rounded edges.  Handrail gripping surfaces should be continuous, and not be uninterrupted by newel posts, other construction elements, or obstructions.  Sidewalks and shared use paths with running slopes steeper than 5 percent should have handrails on both sides, unless the sidewalk or path follows the grade of the adjacent roadway.  Safety railings should be installed when a vertical drop is 30 inches or greater, a downward slope is 2:1 or greater, or a body of water is less than 2 feet from the edge of the sidewalk or shared use path.  Safety railings should be a minimum of 42 inches in height and should have a vertical post so that the space between the vertical posts does not exceed 4 inches width.  Safety railings shall be 42 inches high and should have vertical post spaced no more than 4 inches apart.  Safety railings should have a lateral offset of 1 foot minimum from the edge of the sidewalk.  The ends of the safety railings, barriers, or guardrails should be flared away from the path edge or turned down. Barrier or rail ends that remain within the 2-foot clear area should be marked with object markers.

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 American with Disabilities Act  FHWA, MUTCD Section 9C.07 (latest edition)  FHWA, Rumble Strips and Stripes (latest edition)  FHWA, Separated Bike Lane Planning and Design Guide (latest edition)  GDOT, Design Policy Manual (latest edition)  NACTO, Urban Bikeway Design Guide (latest edition)  NACTO, Urban Street Design Guide (latest edition)  US Access Board, Detectable Warning Update (latest edition)  www.access-board.gov/guidelines-and-standards/streets-sidewalks/public-rights-of-way

Figure 4.13. Pedestrian Safety Railing, Midtown, Atlanta, Georgia

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4.3.4 Fencing for Pedestrian Access Control Fencing may be installed in urban core, urban, suburban, rural, and rural town contexts to delineate the control of access. Fencing could be provided within the right-of-way to define a boundary or a physical barrier to discourage encroachment by pedestrians, bicyclists or animals, or vehicles. Fencing may be placed to delineate outdoor seating adjacent to restaurants or may be required for pedestrian access control in locations where the crossing behavior exhibits poor choices by pedestrians and where a separation is not provided. Fencing may also be provided to restrict access to features such as retaining walls, bridges, and drainage structures. For more information on fencing, refer to the GDOT Design Policy Manual and AASHTO A Policy on Geometric Design of Highways and Streets.

 To delineate the limit-of-access, fencing should be installed within the right-of-way and should be placed a minimum of 1 foot inside the right-of-way to accommodate space required for installation and maintenance.  Fencing should be installed between the roadway and the frontage road .  A 6-foot-high chain link wire fence may be considered around the perimeter of proposed permanent drainage features that hold water over 24 inches deep for greater than 48 hours such as natural ponds, detention ponds, and water quality ponds. This should be evaluated on a case-by-case basis.  Fencing is not required in areas where there are steep slopes or natural barriers or where they are not required to preserve access control.  Fencing installed on private property should be placed a minimum of 1 foot outside the right- of-way.  If fencing is installed on private property by a GDOT contractor, a 5-foot-wide temporary “easement for the construction of fence” is required.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  GDOT, Bridge and Structures Design Manual (latest edition)  GDOT, Construction Standard Specification, Section 643 – Fence  GDOT, Design Policy Manual (latest edition)  GDOT, Right-of-Way Manual (latest edition)

4.3.5 On-Street Parking On-street parking provides a buffer zone between the travel lanes in a roadway and the sidewalk. However, on-street parking near pedestrian crossing locations can interfere with visibility between

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pedestrians and vehicles in the travel lanes. When vehicles are parked too close to marked pedestrian crossings, they may block the line of sight between the driver and the pedestrian stepping off the curb to cross the street. Types of on-street parking include parallel parking, angled parking, and back-in- angled parking.

 On-street parking may be installed on streets in urban core, urban, or rural town contexts on streets with speed limits of 35 mph or less. Proposed on-street parking on a state route would require permission by GDOT.

 On-street parking should be set back a minimum of 20 feet from pedestrian crossings (FHWA 2002).  Minimum parking space dimensions are defined by local agencies. Typical parking space dimensions of 9 feet wide by 24 feet long are desirable for on-street parallel parking stalls. However, in some cases the dimensions are reduced to 7 feet wide and 22 feet long, if allowed by local parking standards.  When perpendicular or angled parking stalls are located adjacent to sidewalks, wheel stops should be installed to prevent the front of the vehicle from protruding into the sidewalk areas. The wheel stops, or curbing, should be located a minimum of 24 inches from the back of the wheel stop to the pedestrian travel zone.  Wherever on-street parking is provided, accessible on-street parking must be included. Refer to PROWAG.

 Curb extensions may be used in combination with on-street parking to increase the visibility of pedestrians waiting to cross the street.  On streets with bike lanes and parallel parking, a 3 to 4-foot buffer between the parking and the bike lane may reduce the risk of bicyclists colliding with car doors.  Front-in-angled parking may be converted into back-in-angled parking to improve the driver’s field of view when pulling out of the space. Back-in-angled parking is particularly useful when angled parking is combined with on-street bike facilities.  On-street parking spaces may be converted into parklets for café seating or pop-up events.  On-street parking spaces may be converted into bike corrals. Refer to Section 6.3.2 for more information on bike parking.

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 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, MUTCD (latest edition)  ITE, Implementing Context Sensitive Designs on Multimodal Corridors Chapter 4 (latest edition)  NACTO, Protected Bike Lane vs. On-street Parking (latest edition)  US Access Board, Proposed Guidelines for Pedestrian Facilities in the Public Right-of-Way (latest edition)

Figure 4.14. Back-In-Angled Parking with Wheel Stops

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Figure 4.15. Example of Temporary On-Street Parking Used for Pop-Up Parklet at the Georgia Walks Summit, Rome, Georgia

4.3.6 Pedestrian Accommodations along Bridges and Constrained Rights-of-Way Bridges provide road users with connections across barriers, such as highways, railroads, and bodies of water. Bridges should be designed with pedestrians in mind.

 Bridges that connect to pedestrian networks should include space for pedestrians and bicycles and should include the appropriate countermeasures to protect both pedestrians and cyclists.

 Pedestrian railings and barriers on bridges should comply with GDOT Bridge and Structures Policy Manual Section 3.3.  Sidewalks on bridges should be a minimum of 5.5 feet wide (GDOT Design Policy Manual).  Shared use paths require a 5-foot buffer from face of curb when they cross bridges. (GDOT Design Policy Manual).

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 When retrofitting existing bridges, excess shoulder space may be used to provide more space for sidewalks and shared use paths.  A best management practice is to consider the use of planters, flexible bollards, or barriers for additional protection.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, MUTCD (latest edition)  GDOT, Design Policy Manual (latest edition)  ITE, Implementing Context Sensitive Designs on Multimodal Corridors Chapter 4 (latest edition)  NACTO, Protected Bike Lane vs. On-street Parking (latest edition)  US Access Board, Proposed Guidelines for Pedestrian Facilities in the Public Right-of-Way (latest edition)

Figure 4.16. Bicycle and Pedestrian Accommodations on Bridges

4.3.7 Raised Medians and Pedestrian Refuge Areas Raised medians and pedestrian refuge areas are spaces intended for pedestrian refuge that are located between active vehicle travel lanes. They are used to break up the total pedestrian crossing distance and provide more protection for pedestrians crossing the street. Raised medians and pedestrian refuge areas are considered traffic calming infrastructure because they effectively narrow the roadway and the field of vision of the approaching motorist, which results in reduced vehicle speeds. According to FHWA Medians and Pedestrian Crossing Islands in Urban and Suburban Areas, Rev 3.0 4. Road and Street Design for Pedestrians 4/25/19 Page 4-32 Pedestrian and Streetscape Guide

studies have shown that raised medians and pedestrian refuge areas reduce pedestrian crashes by 46 percent and 56 percent, respectively.

 Raised medians can help to notify a driver of an upcoming transition from one- character area such as a rural area to a rural town area, or from an “on system” roadway to an “off system” roadway.  Raised medians and pedestrian refuge areas can be installed at intersections or mid-block locations.  Raised medians and refuge areas may be used on two-way streets but are particularly beneficial on streets wider than 60 feet.

 Pedestrian refuge areas should be a minimum of 6 feet wide in the direction of pedestrian travel.  Pedestrian refuge areas should be accessible with either curb ramps or at-grade cut-throughs. At-grade cut-throughs are easier to construct and easier for pedestrians to negotiate than curb ramps, particularly for smaller areas. Additional consideration should be made to accommodate stormwater runoff, so water does not collect or pond on the street or the pedestrian crossing.  At signalized intersections or locations with button-actuated beacons, pedestrian pushbuttons should be mounted in the pedestrian refuge areas to provide pedestrians with the ability to receive the pedestrian signal phase from their refuge position.  Pushbutton posts and other poles should be located outside of the pedestrian travel way and meet MUTCD requirements.

 A median refuge area may be planted with low-growing, low-maintenance plants, which should be selected so that they do not exceed 30 inches in height at maturity.  A best practice is to position reflective, flexible bollards at the leading edge of the raised median or at the pedestrian crossing to improve the driver’s recognition of the pedestrian environment.  A best practice at a mid-block pedestrian crossing is to install a median refuge area alone, without a device such as an RRFB or PHB. The devices may create a false sense of security for pedestrians. In some cases, a median refuge area may provide the most significant safety benefit for the pedestrian.

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 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, MUTCD (latest edition)  FHWA, Safety Benefits of Raised Medians and Pedestrian Refuge Areas (latest edition)  FHWA, State Best Practice Policy for Medians (n.d.)  GDOT, Design Policy Manual (latest edition)  ITE, Implementing Context Sensitive Designs on Multimodal Corridors Chapter 4 (latest edition)  NACTO, Urban Bikeway Design Guide (latest edition)

Figure 4.17. Mid-Block Crossing with Pedestrian Refuge Area, Atlanta, Georgia

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Figure 4.18. Minimum Dimensions of a Pedestrian Refuge Area

4.3.8 Roadway and Lane Diets Wide street crossings can be major impediments to pedestrian access, connectivity, and safety; therefore, a very effective countermeasure for pedestrian safety is a “road diet.” A roadway reconfiguration known as a road diet offers several high-value improvements at a low cost when applied to traditional four-lane undivided highways. The primary benefits of a road diet include enhanced safety, mobility, and access for road users and a "complete streets" environment to accommodate a variety of transportation modes. A classic road diet typically involves converting an existing four-lane, undivided roadway segment to a three-lane segment consisting of two through lanes and a center, two-way left-turn lane. The resulting benefits include a crash reduction of 19 to 47 percent according to FHWA Road Diets/Roadway Reconfiguration, reduced vehicle speed differential, improved mobility and access by all road users, and integration of the roadway into surrounding uses that results in an enhanced quality of life. A key feature of a road diet is that it allows reclaimed space to be allocated for other uses, such as turn lanes, bus lanes, pedestrian refuge islands, bike lanes, sidewalks, bus shelters, parking, or landscaping. Other road diet benefits include:  Reduced rear-end and left-turn crashes due to the dedicated left-turn lane  Reduced right-angle crashes as side street motorists cross three versus four travel lanes  Fewer lanes for pedestrians to cross  Opportunity to install pedestrian refuge islands, bicycle lanes, on-street parking, or transit stops  Traffic calming and more consistent speeds

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 A more community-focused, "Complete Streets" environment that better accommodates the needs of all road users A road diet can be a low-cost safety solution when planned in conjunction with a simple pavement overlay, and the reconfiguration can be accomplished at no additional cost. Road diets or lane diets are not appropriate for all roadways. Careful analysis on determining the feasibility need to be determined up front utilizing traffic count data, existing and proposed ADT, type of road, “off system” or “on system” and the need and purpose of the project to determine whether the street or road you are analysis is suitable for a road or lane diet. FHWA Road Diets/Roadway Reconfiguration states that four-lane, undivided highways experience a number of crash types as traffic volumes increase, including pedestrian crashes due to the high number of lanes for pedestrians to cross with no refuge area. A number of strategies may be considered to reconfigure the street to improve vehicle and pedestrian safety, while simultaneously improving vehicle flow and reducing vehicle speeds. Lane diets and road diets may be used to reduce the width of street crossings and/or the number of lanes that pedestrians must cross. Lane diets involve reducing the width of the travel lanes and road diets involve removing one or more lanes of traffic and, in some cases, reducing the width of the travel lanes. The excess space is converted into space for pedestrians or cyclists, such as wider sidewalks, curb extensions, pedestrian refuge areas, or bicycle facilities. Before proposing a road diet, a comprehensive traffic study should be conducted as well as a land use and walk shed analysis, which identifies existing and future walking and biking destinations. Together, both can help to justify the need and purpose of the project.

 The most typical road diet is the conversion of a four-lane undivided roadway to a three-lane undivided roadway made up of two through lanes and a center two- way left-turn lane utilizing the addition roadway gained for new bike and pedestrian facilities or widening the ones that may have existed. Road Diets provide an opportunity to balance the needs of all transportation users. For examples of types of road diets and when a road diet may be applicable, refer to FHWA Road Diets/Roadway Reconfiguration.

 The minimum lane widths should comply with the specifications outlined in the AASHTO Green Book (latest edition).  Roadway and street geometry should be evaluated along with further engineering judgement to determine the appropriateness of a road diet.

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 When converting a four-lane road into a two-lane road with a two-way left-turn lane, medians or pedestrian refuge areas may be placed at intersections or mid-block pedestrian crossing locations.  The practitioner should determine the types of vehicles that primarily use the street before reducing the lane widths.  A best management practice may be considered for utilizing mountable curbs on narrower lanes to accommodate larger vehicles.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, Road Diets/Roadway Reconfiguration (latest edition)  GDOT, Design Policy Manual (latest edition)  NACTO, Urban Street Design Guide (latest edition)

Figure 4.19. Lane Diet Figure 4.20. Road Diet

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4.3.9 Shared Streets Shared streets are streets where pedestrians, cyclists, transit, and vehicles function without conflicts and are primarily characterized by no expressly designated areas for the movement of any one mode of transportation. On shared streets, all modes of traffic are generally expected to travel at the pace of a pedestrian, the slowest user.

 Shared streets are suitable in areas where pedestrian activity is high and vehicle volumes are low or discouraged.  Shared streets are not appropriate on high vehicle volume streets (greater than 3,500 vehicles per day).

 Shared streets should only be considered on “off system” roads/streets.  Shared streets should have a speed limit of 15 mph or less.

 Signs should be installed to alert motorists to yield to pedestrians.  ADA detectable edges should be used to identify potential hazards for pedestrians with visual impairments.  Materials and street furnishings should be strategically placed to delineate edges and direct the flow of traffic for all users.

 Shared streets may be any width that sufficiently accommodates the modes of transportation that are expected to use the space.  Shared streets may be accommodated with or without a curb.  Special paving features may be used to distinguish unique circulation patterns. Refer to Section 5.2.1 of this Guide for hardscape ideas.  Where sidewalk areas extend into the street, bollards can be used to identify the path of travel as necessary if conflicts between users arise.  Signage to reinforce the posted speed limit may be provided.

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 NACTO, Urban Street Design Guide (latest edition)

Figure 4.21. Shared Street Perspective

4.3.10 Shared Use Paths Shared use paths located in a public right-of-way are physically separated from motor vehicle traffic by an open space, barrier, or grade separation . Like sidewalks, shared use paths can be critical roadway features that support pedestrian mobility and access. Unlike sidewalks, shared use paths can be used by other non-motorized modes of transportation, including, but not limited to, bicycles, rollerblades, and skateboards. Even though shared use paths can be used for recreation, they should be designed for transportation purposes and comply with PROWAG and other national standards for transportation infrastructure.

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 Shared use paths can be installed in urban, suburban, or rural contexts to accommodate pedestrians and bicyclists.  Shared use paths can be located in the public right-of-way adjacent to roadways, along a body of water, or through parks or open space within an independent right-of-way.  Shared use paths are best located on a street or roadway with minimal curb cuts.  Additional considerations must be made to ensure the site visibility is not obstructed at intersections to and from users of the shared use path as well as to and from vehicles approaching, exiting, or entering the intersection.

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 Shared use paths should be a minimum of 10 feet wide, except constrained shared use paths may be as narrow as 8 feet wide (AASHTO Guide for the Development of Bicycle Facilities). A preferred width of a shared use path is 14 feet and sometimes larger in areas with high volumes of pedestrians such as the Beltline in Atlanta, Georgia.  A vertical clearance of 10 feet from fixed objects should be maintained. In some cases, vertical clearance should be taller than 10 feet to accommodate emergency and maintenance vehicles (AASHTO Guide for the Development of Bicycle Facilities).  Horizontal clearance of 2 feet from fixed objects (trees, signs, etc.) should be maintained on each side of the path. Where smooth features such as bicycle railings or fences are introduced with flaring end treatments, a minimum clearance of 1 foot is acceptable. If adequate clearance cannot be provided between the path and lateral obstructions, reflective warning signs and markings should be used to capture the attention of pedestrians (AASHTO Guide for the Development of Bicycle Facilities).  On streets with a speed limit of 35 mph or greater, shared used paths should maintain a 5-foot separation from through travel lanes. If the minimum separation cannot be accommodated, a vertical barrier with a minimum height of 3.5 feet may be needed to separate the path from vehicular traffic in through travel lanes.  On streets with a speed limit greater than 40 mph, the vertical barrier and end treatments should be crash worthy.  Side slopes or ditches should have a minimum of 4 feet of clear, level area (including shoulder) before the up slope or down slope (or ditch) begins.  Where the shared use path is parallel to a street, the grade should not exceed the grade established for the adjacent street.  Drainage grates and inlets should be located at the outside edge or adjacent to shared use paths. Grid style grates are recommended over grates with parallel bars. Grates should be set flush, less than 0.5 inch below the surface of the surrounding pavements, with no raised edges.  Refer to AASHTO Guide for the Development of Bicycle Facilities (2012) for formulas and guidance for calculating the minimum radius for horizontal curves on shared use paths.  Refer to Section 5.2.1 of this Guide for further guidance on material selection (e.g., asphalt or concrete ).

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 A best practice is to provide a 2 percent surface cross slope in one direction, rather than a crowning the trail, to simplify the drainage and surface construction.  In areas with heavy non-motorized volumes, separation of pedestrians from bicyclists may be appropriate.  A 4-inch-wide centerline stripe may be used for shared use paths with heavy volumes of pedestrians and bicyclists, on curves with restricted sight distance, and on paths were night- time use is expected. Shared used paths should be signed and marked.  Reflective edge lines may be beneficial on paths that are intended to accommodate users in dark conditions.  The pathway should not be placed in a narrow corridor or between two opaque fences for long distances. Such conditions create personal security issues, prevent visibility to users who need help, prevent path users from leaving the path in an emergency, and impede the response times for emergency personnel.  When next to a retaining wall, pavement may be extended to the wall face. Narrow (2 feet or less) grass or vegetative buffers should be avoided to simplify maintenance.  Conflicts at intersections and driveways are a major concern for paths adjacent to roadways (see AASHTO Guide for the Development of Bicycle Facilities Section 5.2.2 for more on this topic). Drivers may be less likely to notice non-motorized traffic that is traveling on separated shared use paths adjacent to the roadway.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  AASHTO, Guide for the Development of Bicycle Facilities (latest edition)  GDOT, Design Policy Manual (latest edition)  ITE, Implementing Context Sensitive Designs on Multimodal Corridors Chapter 4 (latest edition)  NACTO, Urban Street Design Guide (latest edition)

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Figure 4.22. Azalea Trail Shared Use Path on Street with speeds less than 35 mph, Valdosta, Georgia

Figure 4.23. Shared Use Path on Street with speeds greater than 35 mph, Brunswick, Georgia

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Figure 4.24. Minimum Width of Shared Use Paths adjacent to low speed street, 35 mph or less

4.3.11 Sidewalks Sidewalks are spaces in the public right-of-way that are dedicated for pedestrian use. They should be designed and built for people of all ages and abilities to use and enjoy. This section provides guidance on the design of sidewalks in different contexts. For further information on sidewalk materials, lighting, and other streetscape amenities, refer to Chapter 6. Chapter 3 describes the importance of a connected and expansive pedestrian network and should be referenced during the scoping and planning phases of a project.

 Sidewalks should be considered during the initial concept phase of a transportation project. The GDOT Complete Streets Policy and Chapter 3 of this Guide provide guidance on when pedestrian accommodations should be implemented.  In urban core, urban, suburban, and rural town areas, where the typical roadway section includes curb and gutter, the sidewalk may be located immediately behind the curb, or preferably offset from the roadway to improve pedestrian comfort.

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 Sidewalks should be a minimum of 5 feet wide, which is the minimum width that accommodates 2 wheelchairs side-by-side. This is also the minimum clear pedestrian zone width as shown in Figure 6.2 of the GDOT Design Policy Manual.  GDOT adopts PROWAG as the standard design policy for ADA-compliant sidewalks.  The grade of sidewalks should not exceed the grade established for the adjacent street or roadway. The running slope of a sidewalk should not exceed 5 percent if not adjacent to a street or roadway.  A maximum of 2 percent cross slope will facilitate adequate drainage on trails and paths. Cross sloping to one side or the other instead of crowning the trail is preferred and may simplify the drainage and surface construction.

 The sidewalk width may vary in response to pedestrian activity, adjacent land uses, and context. Wider sidewalks contribute to placemaking by offering opportunities for landscape, pedestrian scale lighting, sidewalk furnishings, and wayfinding signage, creating an attractive streetscape. A minimum of a 5-foot pedestrian clear zone and a minimum of 5 feet should be maintained for the greenscape/furniture zone.  In areas with high pedestrian activity, the width of the sidewalk (area from curb to edge of right- of-way) may range from 10 to 20 feet.  In areas with relatively low pedestrian activity, the width of a sidewalk (area from curb to edge of right-of-way) ranges from 7 to 12 feet.  Drainage grates and inlets may be located at the outside edge of or adjacent to sidewalks.  Grid-style drainage grates are preferred to drainage grates with parallel bars. Grates should be set flush, less than 0.5 inch below the surface of the surrounding pavements, with no raised edges.  Although 5 feet is the minimum required width of a sidewalk per GDOT’s Design Policy Manual, a best management practice is to provide additional consideration to the existing and anticipated pedestrian volumes so that the appropriate width of the sidewalk is provided.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  GDOT, Design Policy Manual (latest edition)  NACTO, Urban Street Design Guide (latest edition)

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Figure 4.25. Sidewalk in Urban Context Area

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Figure 4.26. Sidewalk in Urban Core Context Area

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Figure 4.27. Sidewalk in Suburban Context Area

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Figure 4.28. Sidewalk in Rural Context Area

Figure 4.29. Sidewalk in Rural Town Context Area

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4.3.12 Transit Stops Transit riders also represent pedestrian trips. Whether catching a bus or getting off a bus, people riding transit expect to cross the street at bus stops. This makes the location of the transit stop in relation to a pedestrian crosswalk especially important. This section provides guidance on transit stop locations and design. For information on the placement and design of amenities, such as benches, maps, and signs, refer to Section 6.3. In areas with a high ridership and sufficient street width, a dedicated bus lane that incorporates bus stops may be utilized. The ability to accommodate a bus lane should be determined based on the available street space and the needs of other modes, including bicyclists, pedestrians, and motorists. The minimum width of a curbside bus lane is 11 feet. The minimum width of an offset bus lane is 10 feet. An offset bus lane is a dedicated bus lane that is typically located between a parallel parking lane and a general through-traffic lane and may be applied to a wide variety of streets. Offset bus lanes are a core part of the transit toolbox for urban streets and are often implemented through simple lane conversions. Offset bus/transit lanes provide priority space for frequent or high-volume transit service, a variety of curbside uses and turning movements, and a comfortable sidewalk environment.

 Transit stops may be located on the near side of an intersection, the far side of an intersection, or at mid-block locations along a roadway. Figure 4.30 through Figure 4.32 to illustrate these options for transit stop locations.  Placing the transit stop at the far side of an intersection or crosswalk is preferred because it minimizes site distance obstructions that may be created by the bus or transit stop related to a transit stop located on the near side of the intersection or crosswalk.  Transit stops are generally best suited for lower speed roadways of 35 mph or less when shared with an active through lane.  Transit stop locations should be evaluated on ridership or demand, locations that are safe for pedestrians to access and are visible for approaching vehicles.

 On streets that serve as a bus route, a minimum 5-foot-wide sidewalk should be provided.  An 8-foot (perpendicular to the curb) by 5-foot (parallel to the curb) passenger loading zone should be provided at the transit stop to accommodate wheelchair lift operation.  The passenger loading zone should be kept clear of obstructions to allow for wheelchair access to transit.  Far-side and near-side bus loading zones should be located a minimum of 20 feet from the crosswalk.  When there is a planting strip adjacent to the curb, a hardscape area that extends from the existing sidewalk to the curb should be provided.

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 Bus bulb-outs may be used on streets with parallel parking to provide passengers adequate area to board or exit the bus without having to step into the street or the stream of pedestrian travel on the adjacent sidewalk.  To accommodate a 40-foot bus, bulb-outs should be 25 feet long (parallel to the curb) by 8 feet wide (perpendicular to the curb).  To accommodate a 60-foot bus, bus bulb-outs should be 45 feet long (parallel to the curb) by 8 feet wide (perpendicular to the curb).  A best practice is for a mid-block transit stop is to locate the transit stop no farther than 200 feet from a marked pedestrian crossing.

Figure 4.30. Example of a Far-Side Transit Stop in Proximity to Marked Crosswalk at Intersection (Preferred Option)

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Figure 4.31. Example of a Near-Side Transit Stop in Proximity to Marked Crosswalks at Intersection

Figure 4.32. Example of a Mid-Block Transit Stop with Mid-Block Crosswalk

4.4 Intersection Design Intersections are where two or more streets meet or cross each other at the same grade. With vehicles, freight, transit, pedestrians, and bicycles using intersections for both crossing and turning onto other streets, intersection activity may become complicated and result in the potential for conflicts. Intersection design should take a balanced approach to meet the needs of all modes of transportation.

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Because of the multi-mode nature of intersection activity and the need to efficiently accommodate multiple modes and movements, intersections may be challenging parts of a street to design. Traditionally, vehicle movements and delay have been given the highest priority and has influenced intersection geometry. However, the optimal intersection design for vehicles may overlook the needs of pedestrians. This section offers guidance on how to balance the needs of both motorists and pedestrians in the design of controlled and uncontrolled intersections, supporting convenient pedestrian access while enabling drivers, pedestrians, and bicyclists to be aware of one another.

4.4.1 Channelized Right-Turn Lanes Channelized right-turn lanes are right-turn-only lanes with no stop control and therefore introduce a potential conflict between an automobile and a pedestrian. Careful design and pedestrian safety countermeasures should be considered when proposing a channelized right-turn lane. The large turning radii enable drivers to maintain a high speed, which creates a challenging environment for pedestrians crossing the intersection. Channelized right-turn lanes create a wider intersection, increasing the crossing distance for pedestrians. Intersections with channelized right-turn lanes may be retrofitted by adding a pedestrian refuge area, which effectively reduces the corner radii and pedestrian crossing distance. Traffic calming measures that may be considered include smaller corner radii and raised crosswalks to encourage vehicles to slow down as they approach the turning movement.

 Channelized right-turn islands may be appropriate where large curb return radii, such as those greater than 30 feet, are required to serve large vehicles.  Channelized right-turn islands are typically not appropriate for an urban core, urban, or rural town context or areas with high pedestrian volumes or areas with a significant population of disabled people.  If the project’s primary need and purpose is to reduce traffic delay and support the need for a channelized right-turn lane. Pedestrian safety countermeasures should be carefully evaluated to offset potential conflicts between automobiles and vehicles.  Channelized right-turns are typically more appropriate in automobile dependent land use or suburban context. They typically are not well suited for an urban core or urban context.

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 The refuge island should be raised to provide a vertical barrier so that the pedestrian refuge area has greater protection from vehicle intrusion.  Raised refuge areas should provide curb ramps from the sidewalk to the raised island or provide pedestrian cut throughs with detectable pavers.  If space is limited in the island, a minimum 6-foot-wide cut through should be provided in the island for accessible pedestrian passage.  The pedestrian refuge island should be clear of visual obstructions, including utility facilities and landscaping taller than 2 feet.  The crosswalk should be placed perpendicular to the travel lane so that it crosses the channelized right-turn lane at 90 degrees or diagonal where the pedestrian is always facing traffic.

 The crossing point may be marked with a high-visibility crosswalk design and a stop bar.  A best practice is to apply the elongated tail design for refuge areas, which provides a more direct line-of-sight between the driver and the pedestrian crossing and reduces the effective speed of the turning vehicle. In addition, the elongated tail design improves the angle between the turning vehicle and the oncoming traffic to which the turning vehicle should stop or yield, which otherwise requires a driver to turn their head to an angle that is either uncomfortable or difficult for some drivers. The elongated tail design improves the pedestrian environment and the driver environment as compared to a simple radius curve.

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Figure 4.33. Example of a Channelized Right-Turn with an Elongated Island

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, MUTCD (latest edition)  GDOT, Design Policy Manual (latest edition)  NACTO, Urban Street Design Guide (latest edition)

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4.4.2 Corner Extensions Corner extensions reduce crossing distances and make pedestrians more visible to motorists at intersections. In addition, corner extensions provide traffic calming benefits, including a speed reduction for turning traffic and through traffic.

 Corner extensions should be considered where on-street parking exists, to provide pedestrians waiting at an intersection crosswalk with a place to stand with improved visibility to oncoming vehicles and from drivers.  Corner extensions should be considered in cases where a turn lane is discontinued across an intersection or where a lane terminates on one side of the intersection.  Corner extensions should only be used on a street with a curb.  Corner extensions are appropriate for speed limits up to 40 mph.  Corner extensions may not be appropriate where larger vehicles, emergency vehicles, and buses make frequent turning movements.  Corner extensions may be used for one or both sides of an intersection crossing, and for one or both sides of a corner that serves two crosswalks.

 Corner extensions should be offset from the traffic lane by 1.5 feet.  Corner extensions should be a minimum of 6 feet wide.

 On streets with on-street parking, corner extensions improve visibility for pedestrians at an intersection and drivers approaching the intersection.  Corner extensions may provide additional space for streetscape amenities (e.g., trash cans, bicycle racks, benches).

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Figure 4.34. Typical Dimensions of a Curb Extension

4.4.3 Corner Radii At intersections with pedestrian crossing activity and only limited truck and bus turning movements, the curb radii should be designed to improve the pedestrian environment. The selection of curb radii applies to a typical corner design, and the design of curb extensions and/or bulb outs. A smaller curb radius at an intersection shortens the pedestrian crossing distance and reduces vehicle turning speeds.

 A range of corner radii of 15 to 25 feet may be appropriate at minor cross street intersections where truck turning movements seldom occur or at major intersections where there in on-street parking located close to the intersection.

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 Several basic parameters should be considered in determining corner radii such as context of the area, such as urban core, urban, suburban, rural town, or rural. Additionally, existing and future developments that may or may not need larger turning radii to accommodate truck movements should be evaluated. Other factors to consider include, but are not limited to, pedestrian volumes, vehicle speeds, intersection angle, number and width of lanes, design vehicle, turning path, clearances, encroachment into oncoming or opposing lanes, parking lanes, and shoulder widths.  Vehicle operations should be balanced with the needs of pedestrians and the difficulty of acquiring additional right-of-way to accommodate corner setbacks on private property.  A range of corner radii of 15 to 25 feet are adequate to support the turning movement for passenger vehicles for streets with speed limits of 35 mph or less.  Where larger radii are used, a pedestrian refuge area or median island should be installed.  Corner radii may be designed with turning design speeds of 15 mph or less. See Section 4.4.2 for further information.

 Locate fixed objects clear from the curb radius to avoid obstructing the sight lines between pedestrians and drivers, and to provide an allowance for the occasional large vehicles that cannot maneuver the turning movement without driving over the curb.  Considerations for mountable curbs should be made for vehicles with larger turning movements.  The GDOT Design Policy Manual explains that corner radii at intersections are design elements that affect the operation, safety, and construction costs of the intersection.

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4.4.4 Curb Ramps Curb ramps provide access onto and off the sidewalk for pedestrians of all abilities. GDOT provides details for multiple ADA ramp configurations. Refer to GDOT Construction Detail T-11A for specific design criteria and additional guidance.

 ADA-compliant curb ramps should be installed at marked crosswalk locations.  Curb ramps should be installed on medians or channelized islands that serve as pedestrian refuge areas, unless an at-grade cut-through opening is provided.

Figure 4.35. Example of Curb Ramp

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 Curb ramps should comply with GDOT Construction Detail A-3 and Construction Detail A-4.  The low end of the curb cut should meet the grade of the street with a smooth transition.  At locations where there is sufficient space, perpendicular curb ramps are preferred.  Perpendicular curb ramps should have flat flared sides with a maximum slope of 10 percent measured parallel to the curb line.  At locations where there is not sufficient space to provide an appropriately sized landing area at the top of the curb ramp, a parallel curb ramp should be used. See GDOT Construction Detail T-11A.  ADA parallel curb ramps should have a longitudinal running slope that is in line with the direction of sidewalk travel and have the appropriate sized landings per GDOT Construction Detail T- 11A.  Curb ramps or pads should include an ADA detectable edge that extends the full width of curb ramp (exclusive of the flared sides) and is a minimum of 24 inches wide, measured from the edge of the curb closest to the street. Refer to PROWAG and Section 4.3.1 for more information on the design of ADA detectable edges.  Curb ramps should align with and be fully incorporated within the corresponding crosswalk.  Storm drainage inlets should be placed on the uphill side of crosswalks and curb ramps to avoid excessive drainage flows across the crossing area. Adequate drainage should be provided at intersection corners so that standing water does not accumulate within the crossing area or at the bottom of the ADA ramp.  The maximum cross slope for an ADA accessible facility shall not exceed 2 percent.

 A best practice is to retain a project designer to conduct construction observation services with respect to ADA facility construction.  A best practice is for the designer to approve ADA facilities for compliance prior to closing out the construction project.

 American with Disabilities Act  GDOT, Construction Detail T-11A  GDOT, Design Policy Manual (latest edition)  US Access Board, Detectable Warning Update (latest edition)

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4.4.5 Diverging Diamond Interchanges The diverging diamond interchange (DDI), also known as a double crossover diamond, is a diamond interchange that directs traffic to the opposite side of the road so that vehicles may make unimpeded movements onto freeway ramps. DDIs may be challenging places for pedestrians because of the unsignalized, channelized turn lanes and longer crossing distances and vehicles traveling on the left side of the road and approaching crosswalks from the opposite direction. Countermeasures may be applied to create a more comfortable walking environment for pedestrians.

 If pedestrian accommodations are warranted by the GDOT Complete Streets Policy, sidewalks or center walkways and crosswalks should be provided at DDIs.  Shorter crossing distances may be achieved by placing sidewalks along the perimeter of the DDI. However, the primary challenges with this design are that pedestrians must cross unsignalized, channelized right-turn and left-turn lanes, and they cannot cross the arterial at this interchange.  Center walkways may be used to reduce the number of times a pedestrian has to cross an unsignalized, channelized turn lane. The crossings from the channelized island to the center walkway are signalized, while the crossings from the island across the right-turn lanes are often unsignalized. The primary challenge with this design is the long crossing distance between the channelizing island and the center walkway.

Image provided by Google Earth.

Figure 4.36. Example of a Diverging Diamond Interchange, Ashford Dunwoody Road, Dunwoody, Georgia

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 High-visibility crosswalks and ADA curb ramps should be placed at pedestrian crossing points. Refer to Sections 4.4.8 and 4.4.4 for more information on crosswalks and curb ramps, respectively.  The line of sight between motorists and pedestrians waiting at a crossing point should not be obstructed.  Sidewalks along the perimeter should be designed in accordance with recommendations in Section 4.3.11.  Center walkways should be a minimum of 8 feet wide (12 feet preferred) (two 1.5-foot-wide barriers and one 5- to-8-foot-wide pedestrian access route).  Cut throughs or curb ramps with detectable edges should be provided at both ends of the center walkway and aligned with the crosswalks. The cut through should be a minimum of 6 feet wide (the distance between the end of the vertical barrier and the raised splitter island at the point of the center walkway).  The center walkway should have a positive slope so that water does not collect or pond within the pedestrian facility.  All ADA accessible codes must be met with the center walkway.  Center walkways shall be separated from vehicular traffic by a vertical barrier. The vertical barrier should be a minimum 3.5 feet tall. The vertical barrier should not be so tall that it creates a tunnel or obstructs the view between pedestrians and motorists.  The outside edge of the center walkway vertical barrier should be offset a minimum of 2 feet from the vehicle travel path.  Right-turn and left-turn channelizing islands should be designed as pedestrian refuge areas with a minimum width of 6 feet in the direction of pedestrian travel. Refer to Section 4.3.7 for more information on the design of pedestrian refuge areas.  Pedestrian signals and pushbuttons should be placed on either side of a signalized crossing.  The lighting design for sidewalks, center walkways, and crossing points at a DDI should follow the same considerations as at other interchanges.

 Pedestrians may not expect traffic to be approaching from the opposite direction. Design elements, such as sidewalk markings, may encourage pedestrians to look in the direction of oncoming traffic.  The radius for unsignalized, channelized turns may be reduced to slow down turning vehicles.  Recessed lights may be used in the center walkway to provide adequate lighting when space is limited.

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 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, Alternative Intersections/Interchanges: Informational Report (latest edition)  FHWA, Diverging Diamond Interchange Informational Guide (latest edition)  GDOT, Design Policy Manual (latest edition)  Schroeder, Observations of Pedestrian Behavior and Facilities at Diverging Diamond Interchanges (latest edition)

4.4.6 Diverters Diverters are physical barriers that redirect vehicular traffic while maintaining through access for pedestrians and bicyclists. These traffic calming features reduce vehicle volumes, cut-through traffic, and speeds by restricting through movements or certain turn movements. Diverters may either completely or partially close off access to an adjacent street.

 Diverters may be used on low-volume, low-speed streets (25 mph or less).  The potential street network implications of limiting traffic movement with an interconnected pattern of streets should be considered. To this extent, traffic diverters may be used as part of a larger traffic management strategy.

 Pedestrian and bicycle pass throughs should be incorporated into diverters to provide access through the closed area.  The impact of diverters on stormwater drainage should be considered.

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 If emergency vehicles require access through the diverter, the diverter design may include a minimum 12-foot-wide limited-access lane (14 feet is preferred) that is clearly signed and marked for emergency vehicles only. It may also include breakaway or lockable bollards or gates.  Raised diverters may be designed to incorporate green stormwater infrastructure. Raised green infrastructure diverters are not allowed “on-system” or State Routes.  A best management practice is to provide warning signage to alert motorists of changes in the roadway.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, MUTCD (latest edition)  FHWA, Traffic Calming ePrimer (latest edition)  GDOT, Design Policy Manual (latest edition)  NACTO, Urban Street Design Guide (latest edition)

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Figure 4.37. Example of a Diverter, Brookhaven, GA.

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4.4.7 Driveway Crossings Driveways are vehicle access facilities that connect a roadway to the adjacent property or to a street. Driveways represent a conflict point between vehicles and pedestrians on sidewalks, and with cyclists if the facility is a shared use path or cycle track. Driveways that cross sidewalks and shared use paths may be challenging because drivers that are entering or exiting a driveway are often focused on the flow of vehicular traffic, and do not notice pedestrians crossing the driveway. The raised driveway crossing countermeasure improves visibility of the pedestrian or cyclists crossing the driveway. In addition, the elevated driveway reduces the speed of vehicles entering and exiting the driveway. GDOT complies with the guidelines set forth in AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition).

 The guidelines provided in this section are more appropriate on driveways with gentle slopes and with good visibility for drivers and pedestrians.

 Sight-distance requirements from the driveway to the sidewalk or shared use path are critical; see the MUTCD for further guidance.  Driveways should be designed to accommodate emergency vehicles.  Driveways should meet sidewalks and shared use paths at right angles.  Driveways should not interrupt the grade of the sidewalk.  In general, commercial driveways should be no more than 30 feet wide; check local ordinances that may apply.

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Figure 4.38. Example of Driveway Crossing Sidewalk, Atlanta, Georgia

 Driveways should be designed so that the sidewalk is a visible feature where they intersect.  The driveway may meet the sidewalk at sidewalk grade to eliminate the need to provide ADA transition slopes across the driveway. This may also help reduce the speeds of approaching vehicles.  Careful consideration should be made to address stormwater so that ponding or standing water is not present or trapped after a rain event at the raised crossing.  For locations where sight distance is insufficient, signs, or mirrors may be located to the side of the pedestrian travel way, and auditory warnings may be provided when vehicles are entering and exiting (such as entrances or exits for parking garages) to notify pedestrians that they are entering a vehicle travel path. In addition, careful consideration should be made to prevent glare from the mirror to the roadway or the approaching pedestrian or bike facility.  As a best practice, sidewalk materials may continue across the driveway to alert drivers of an intersection with a pedestrian crossing.  As a best practice, additional consideration should be made in regard to applying raised driveway crossings, as they tend to work best on driveways with flat and straight approaches.

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4.4.8 Marked Crosswalks Marked crosswalks are designated locations for pedestrians to cross the street. Marked crosswalks provide an indication to pedestrians as to where they should cross the street and to motorists as to where pedestrians are likely to be crossing the street. For “on system” roadways, the design of crosswalks should be in accordance with the GDOT details and the MUTCD. Crosswalk patterns should be striped per GDOT Construction Detail T-11A. For “off system” or local streets, and the local government prefers to stripe a crosswalk with a different pavement striping pattern, it should comply with the MUTCD.

 Marked crosswalks should be installed on all approaches at signalized intersections connecting adjacent (or future) sidewalks. Exceptions normally granted by GDOT include pedestrian crossings adjacent to highway-rail crossings where a preemptive signal is used to clear the tracks.  Marked crosswalks may also be installed at mid-block locations. Refer to Appendix A for further guidance on determining the location for and designing crossings at uncontrolled locations.  A best practice is to provide pavement markings and signage at marked crosswalks.  For “on system” locations, a crosswalk may remain unmarked if the GDOT requirements found in Appendix A, Table A-5 are not met.  For “off system” locations, a best practice is to follow the procedure found in Appendix A for consistency of crosswalk application throughout Georgia.

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Figure 4.39. Example of Crosswalk Markings

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 Crosswalk markings should be high visibility, non-slip, and should comply with GDOT Construction Detail T-11A.  Crosswalks should provide the most direct connection between sidewalks or shared use paths.  Crosswalks should align with the corresponding curb ramp.  Crosswalks should always have a corresponding curb ramp when connecting to a sidewalk placed on a curb above the crosswalk elevation, regardless of whether the crosswalk is marked.  Crosswalks should extend the full width of the roadway.  Crosswalks should be a minimum of 8 feet wide.  A stop bar should be located a minimum of 8 feet upstream from the crosswalk to reinforce yielding to pedestrians.  If stop lines are used at a crosswalk that crosses an uncontrolled multi-lane approach, Stop Here for Pedestrians (R1-5 Series) signs should be used.  In urban areas where crosswalks exist, signs should not be placed within 4 feet in advance of the crosswalk so that people who are wheelchair dependent may easily maneuver the access to the ADA ramp.  Drainage inlets should be located on the uphill side of crosswalks and curb ramps to intercept stormwater runoff, so that standing water or ponding does not occur within the crosswalk.  Crosswalk pavement markings should be white with reflective properties meeting MUTCD.  Solid white lines should mark the crosswalk. The crosswalk should not be less than 6 inches or greater than 24 inches in width.  GDOT prefers both transverse (“bar pairs”) and parallel lines be used.  FHWA Interpretation Letter 3(09)-24(I) – Application of Colored Pavement clearly describes acceptable and unacceptable color and pattern treatments for crosswalks. Local governments should refer to this ruling when considering designs that differ from GDOT Construction Detail T- 11A.

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 Raised crosswalks may be used at mid-block crossing locations and in channelized right-turn lanes. Refer to Section 4.4.11 for further guidance on the design of raised crosswalks.  Further evaluation should be made to develop the right tool kit of countermeasures to provide optimal conditions for a pedestrian.  Crosswalks may be painted with non-slip and high-visibility paint to enhance the roughness coefficient and visibility of a crosswalk. Refer to FHWA Interpretation Letter 3(09)-24(I) – Application of Colored Pavement, which clearly describes acceptable and unacceptable color and pattern treatments for crosswalks.  In-street pedestrian crossing signs may be placed in the roadway center line within the crosswalk, on a lane line, or on a median island. The in-street pedestrian crossing sign should not be mounted on a fixed post located either on the left-hand or right-hand side of the roadway.  Scored or stamped and colored concrete surfaces may be used as a placemaking tool. Special paving surfaces should be installed and maintained in a smooth, level, and clean condition.  When using stamped, colored asphalt, concrete or brick materials for crosswalks, as a best management practice, it is recommended that GDOT Construction Detail T-11A be applied to the top surface for additional visibility of the crosswalk.  Pavement marking contrast with the pavement is important to distinguish the roadway or street material from the crosswalk material or treatment.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, Interpretation Letter 3(09)-24(I) – Application of Colored Pavement  FHWA, MUTCD (latest edition)  GDOT, Design Policy Manual (latest edition)

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Figure 4.40. Crosswalk Markings and Dimensions

4.4.9 Pedestrian Bridges and Underpasses Pedestrian bridges and underpasses are grade-separated crossings that allow pedestrians and bicyclists to cross barriers such as multi-lane, high-speed roads and rivers. Like shared use paths, bridges and underpasses separate pedestrians and bicyclists from vehicles and may make crossing the street safer and accessible for people of all ages and abilities but must be convenient and accessible for all users. Pedestrian bridges and underpasses may be very expensive, present challenges for convenient access, and may present users with perceptions related to the fear of heights, increased criminal activity, and convenience as compared to an at-grade crossing. In addition, grade-separated facilities may also increase delay for a pedestrian or cyclist depending on the access points. In most cases, stairs, ramps, or elevators are required to provide access for all users. Pedestrians may choose to cross the street at-grade whether the at-grade crossing is designed for pedestrian activity or not. On example where both pedestrians and bicycles are not allowed is on limited access facilities some examples of limited access facilities in Georgia are I-75, I-85 and I-20.

 Grade-separated crossings may be appropriate when the pedestrian network is interrupted by multi-lane, high-speed roads, railroads, or natural barriers.  Pedestrian bridges and underpasses may be considered at intersections where there is a high rate of pedestrian-vehicle conflicts or potential pedestrian-vehicle collisions. Pedestrian countermeasures for improving the at-grade crossing should also be evaluated as they may be more effective and more practical and should be explored first.  Pedestrian bridges and underpasses may be considered at crossing locations where children are crossing (or anticipated to cross) major multi-lane, high-speed roads.

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Bridges  Bridges should be designed for pedestrian live loadings. Where maintenance and emergency vehicles may be expected to cross the bridge, the design should accommodate them.  Pedestrian bridges should be ADA accessible.  Pedestrian bridges should have a minimum width of 8 feet.  If accommodating bicycles, pedestrian bridges should be a minimum of 14 feet wide.  For pedestrian bridges, the receiving clear width on the end of a bridge (from inside of rail or barrier to inside of opposite rail or barrier) should allow 2 feet of clearance on each side of the pathway. Under constrained conditions the clear width may taper to the pathway width.  Pedestrian bridges should have 42-inch railings on both sides.  The minimum clearance of a bridge structure to a shared path or roadway is 17’-6”, please see GDOT 2.3.3.1 for further guidance, GDOT Bridge and Structures Design Manual.  Bridge spans over roads or railroads shall be long enough to span the travel way, drainage ditches, shoulders, sidewalks, clear zone for the travel way, and the offset distance from the toe of slope paving or face of abutment wall (See Sections 2.3.3 and 2.3.4) of GDOT Bridge and Structures Manual.  The primary purpose of a bridge fencing project is to create a raised barrier that will deter persons from dropping or throwing objects from the bridge onto vehicles or pedestrians below the bridge. The raised barrier on bridge fencing projects is typically a fence that is added to an existing bridge. The project limits should be defined as the extent required to accommodate the bridge fencing. Standard fence details should be utilized whenever possible. See 11.2.1 Bridge Fencing Projects for additional guidance, GDOT, Design Policy Manual. Underpasses  Underpasses should have a minimum width of 14 feet.  Underpasses over 60 feet long should be wider than 16 feet.  Underpasses should have a minimum of 10 feet vertical clearance (AASHTO Guide for the Development of Bicycle Facilities Section 5.2.10).  Lighting of at least 10 foot-candles should be provided in pedestrian tunnels to improve pedestrian safety/security. In addition, variable level lighting (to match outdoor lighting levels) should be used in pedestrian underpasses to accommodate persons whose eyes adapt slowly to lighting changes.  White walls and roof openings may be used to increase lighting levels in tunnels.  Warning signs indicating that the tunnel or underpass should not be used during high-water events should be provided at both entrances.  Exit of the underpass should be visible from the entry.

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 Bridges and underpasses with entrances that are wider than the pathway is more inviting for pedestrians and bicyclists.  Pedestrians and bicyclists are unlikely to use a bridge or an underpass if a more direct route is available.  Signs alerting pedestrians and bicyclists of the clearance height may be provided at bridge and underpass entrances.  For underpasses that accommodate bicycles, reflective centerline striping may be used to avoid collisions during dark hours.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  AASHTO, Guide for the Development of Bicycle Facilities (latest edition)  AASHTO, Guide Specifications for Design of FRP Pedestrian Bridges (latest edition)  AASHTO, LRFD Bridge Design Specifications (latest edition)  FHWA, MUTCD (latest edition)  GDOT, Bridge Structures and Design Manual (latest edition)  GDOT, Design Policy Manual (latest edition)  Rails to Trails Conservancy, Tunnels and Underpasses (latest edition)

Figure 4.41. Retrofitted Train Trestle Pedestrian Bridge, Rome, Georgia Rev 3.0 4. Road and Street Design for Pedestrians 4/25/19 Page 4-74 Pedestrian and Streetscape Guide

4.4.10 Protected Intersections At a protected intersection , bicycles and pedestrians are separated from vehicle movements up to the vehicle lane crossing point. The separation is provided by placing raised islands at the corner between the vehicle lane and a separated bike lane. The corner refuge island allows the bike lane to be physically separated from motor vehicles up to the intersection crossing point, where potential conflicts with turning motorists may be controlled more easily. Corner refuge islands are used to maintain at-grade crosswalks across the entire roadway for crossing pedestrians.

 Protected intersections are used in conjunction with separated or on-street bike facilities.  Protected intersections are appropriate on streets in areas such as an urban core, urban, or rural town with a high volume of pedestrians and cyclists.  Protected intersections are appropriate on streets with a speed limit of 35 mph or less.

 If the raised islands that form the protected intersection are located within a pedestrian crossing path, they should be designed in accordance with PROWAG. Refer to Section 4.4.12 for information on the design of raised islands in protected intersections.

 A separated signal phase for turning traffic may be used to eliminate conflicts between vehicles, bicycles, and pedestrians.  An apron located on the corner to accommodate large vehicles may be used in locations where large vehicles and buses are expected to make right turn movements.

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Figure 4.42. Protected Intersection – Urban Core

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4.4.11 Raised Crosswalks Speed tables used at pedestrian crossings are commonly referred to as raised crosswalks. Raised crosswalks have similar design standards to speed tables and speed humps and are marked and signed as designated crossings. Raised crosswalks are effective for reducing vehicle speeds and drawing attention to the pedestrian crossing. Raised crosswalks provide significant benefits to the pedestrian environment as they improve drivers’ awareness of pedestrian crossings.

 Raised crosswalks should be marked with high-visibility crosswalk design features or alternatively they may be surfaced with different paving materials.  Raised crosswalks are appropriate at mid-block locations on streets with a speed limit of 30 mph or less.

 Raised crosswalks may be used in areas with high pedestrian crossing activity, such as main streets, urban areas, airport drop-off and pickup zones, shopping centers, and academic or institutional campuses.  Raised crosswalks may be used at uncontrolled pedestrian crossing locations to enhance the marked crossing.  Raised crosswalks may be used at intersections as a gateway element to distinguish transitions to pedestrian-oriented areas that require slower vehicle speeds.  May not be appropriate on steep grades.

 Raised crosswalks should extend curb-to-curb and be level with the adjacent sidewalks.  Raised crosswalks should be highly visible, either striped as a marked crosswalk or constructed of a contrasting pavement design.  A detectable edge should be used to distinguish the end of the sidewalk and the beginning of the roadway to assist visually impaired persons.

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 A raised crossing may be 22 feet long in the direction of travel and include two 6-foot parabolic ramps on each end of a 10- to-12-foot flat section. The length may vary to align with the width of the adjacent sidewalk or shared use path.  To maintain stormwater drainage channels, the raised crossing may be placed 1 to 2.5 feet from the curb. A flat cap that is flush with the adjacent sidewalks should bridge the gap between the sidewalk and the speed hump to comply with ADA.  If the raised crosswalk extends to the edge of the curb, additional catch basins may be needed to handle interrupted gutter flow.  Additional considerations should be made to accommodate large vehicles.  Additional consideration should be made to ensure standing water or ponding does not occur at the base of the raised crosswalk.

Figure 4.43. Raised Crosswalk for Shared Use Path Crossing

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4.4.12 Raised Intersections A raised intersection is a flat, raised area covering an intersection with ramps on all vehicle approaches. Similar to speed tables, raised intersections are effective in reducing vehicle speed to a range of 25 to 35 mph when crossing the intersection.

 Raised intersections are applicable on one-way or two-way local streets with a speed limit of 35 mph or less, and a maximum daily vehicle volume of 10,000 vehicles.  Raised intersections are appropriate at controlled intersections with a large volume of pedestrians crossing.

 The vehicle ramp onto the raised intersection should be sloped at a 5 percent minimum to 8 percent maximum grade from the roadway approach to the top of the raised intersection surface.  While raised intersections make it easier to meet ADA requirements as the crosswalk is a natural extension of the sidewalk with no change in grade, the diminished curb line makes it more difficult for sight-impaired pedestrians to detect the edge of the roadway. To this extent, special treatment such as detectable warning truncated domes should be used where the sidewalk transitions to a crosswalk.  The pedestrian travel path and the vehicle path should be differenced with pavement marking or special paving materials.

 Bollards may be used to delineate the corner radii in flush pavement conditions.  Raised intersections may serve as a gateway treatment on main streets and urban areas.  Additional drainage inlets may be required where the raised intersection grade returns to street level.

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Figure 4.44. Raised Intersection

4.4.13 Roundabouts A roundabout is a circular unsignalized intersection with a raised circular island in the center. There are many types of roundabouts, such as mini roundabouts, single lane roundabouts, and multi-lane roundabouts, all of which are effective in reducing vehicle speeds. Roundabouts differ from traffic circles in that they include truck aprons and splitter islands and approaching drivers must yield to traffic in the roundabout. In addition, approaching vehicles must stop for pedestrians who are at the crosswalk. Similar to medians and pedestrian refuge areas, splitter islands are important for accommodating pedestrians at roundabouts because they simplify the street crossing task to one direction of vehicle travel at a time, provide a more protected pedestrian crossing, and reduce the time that pedestrians are exposed to vehicles across the travel lane. In addition, roundabouts are effective in reducing vehicle speeds and in minimizing high-speed crashes that result in severe injuries.

 Roundabouts are appropriate treatments at intersections on local, collector, and arterial streets with posted speed limits of up to 45 mph.

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 Crosswalks (or cut throughs for bike crossings) at roundabouts should be located 20 to 70 feet upstream from the yield line to accommodate one to two vehicles stopped between the crosswalk and the entrance line (FHWA Roundabouts: Technical Summary 2010).  The crosswalk should be perpendicular to the centerline of the approach roadway.  Splitter islands should be at least 6 feet wide at the crosswalk in the direction of pedestrian travel.  Walkways through the splitter island should be cut through instead of ramped.  The cut-through width should be the same width as the crosswalk.  Curb ramps should be provided from the sidewalks at each end of the crosswalk.  A detectable warning surface on splitter islands should begin at the curb line and extend 2 feet into the cut-through area, leaving a clearance of at least 2 feet between detectable warning surfaces.  Where sidewalks are flush against the edge of the curb at roundabouts, and pedestrian street crossing is not intended, a continuous and detectable edge treatment should be provided along the street side of the sidewalk. Detectable warning surfaces should not be used for edge treatments. Where chains, fencing, or railings are used for edge protection, the bottom edge of the treatment should be 15 inches maximum above the sidewalk to be detectable by a cane.  “Stop Here for Pedestrians” signs (R1-5 series) should not be used in advance of a crosswalk at a roundabout because these signs may potentially add to the sign clutter and confuse drivers.  “Pedestrian Crossing” signs (W11-2) supplemented with a diagonal downward-pointing arrow plaque (W16-7P) should be used at the pedestrian crossing but should not be used in advance of the crossing.  Adequate illumination should be provided for pedestrian crossings. Lighting should be placed upstream (at the approach) of a crosswalk on both sides of the crosswalk.

 Pedestrian signals, PHBs, or pedestrian warning beacons may be installed at roundabouts where there are (1) high vehicular volumes and insufficient gaps in vehicular traffic for pedestrians to cross, (2) high pedestrian volumes with continuous or frequent pedestrian crossing activity, or (3) complex crossing situations, such as two traffic lanes in each direction. Refer to Chapter 5 for further guidance on the application of each treatment.  A best practice is to use mountable curbs for truck aprons.

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 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, MUTCD (latest edition)  GDOT, Design Policy Manual (latest edition)  NACTO, Urban Street Design Guide (latest edition)  TRB, NCHRP 672 (latest edition)

Figure 4.45. Dimensions of Crosswalks at a Roundabout

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4.4.14 Single-Point Urban Interchanges A single-point urban interchange (SPUI) uses split-phase signals and channelizing islands to consolidate opposing left-turn movements to one signal phase and direct traffic flow, respectively. While the primary purpose of an SPUI is to increase vehicle capacity and flow, these interchanges may be designed to accommodate pedestrians.

 If warranted by GDOT Complete Streets Policy, sidewalks, curb ramps, and crosswalks should be provided at SPUIs.

 Pedestrians should not cross the road in one signal phase at SPUIs. Instead, the crossing should be broken up into several stages. To accommodate, medians and channelizing right- and left-turn islands should be designed as pedestrian refuge areas. Pedestrian refuge areas should be designed in accordance with the recommendations in Section 4.3.7.  High-visibility crosswalks and ADA curb ramps should be placed at all crossing points. Refer to Sections 4.4.8 and 4.4.4 for more information on crosswalks and curb ramps, respectively.  Pedestrian signals and pushbuttons should be placed on both sides of pedestrian refuge areas if pedestrians are expected to wait and cross the road in two separate signal phases.

 The radius for unsignalized, channelized turns may be made smaller to reduce the speed of turning vehicles.  A two-stage pedestrian signal phase may be used as an alternative to a separate pedestrian phase. This signal design allows pedestrians to cross half of the road during the first left-turn phase and complete the crossing during the second left-turn phase.

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 California Department of Transportation, Complete Intersections: A Guide to Reconstructing Intersections and Interchanges for Bicyclists and Pedestrians (latest edition)  FHWA, Alternative Intersections/Interchanges: Informational Report (latest edition)  FHWA, Median U-Turn Intersection, Informational Guide (latest edition)  FHWA, Restricted Crossing U-Turn Intersection, Informational Guide (latest edition)  ITE, Recommended Design Guidelines to Accommodate Pedestrians and Bicycles at Interchanges (latest edition)  Missouri Department of Transportation, Design of Single-point Urban Interchanges (latest edition)

4.4.15 Skewed Intersections Skewed intersections occur when two streets meet at angles other than 90 degrees. Skewed intersections are discouraged for new construction, since the intersection geometry does not promote pedestrian safety. Existing skewed intersections that may not be realigned should be considered for countermeasures that may improve pedestrian safety. Skewed intersections may be uncomfortable places for pedestrians to cross because of longer crossing distances, decreased visibility between pedestrians and drivers, and potentially high turning speeds.

 If warranted by the GDOT Complete Streets Policy, sidewalks, curb ramps, and crosswalks should be provided on either side of the street and across each leg of the intersection.

 High-visibility crosswalks and ADA curb ramps should be placed at all crossing points. Refer to Sections 4.4.8 and 4.4.4 for more information on crosswalks and curb ramps, respectively.

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 If there is adequate right-of-way, skewed intersections should be realigned as close to 90 degrees as possible, AASHTO recommends a minimum of 75 degrees.  Curb extensions may be installed to shorten crossing distances, slow down turning vehicles, and in some cases adjust the skew.  Medians with pedestrian refuge areas may be installed on wide roads where pedestrian crossings may need to be accommodated in two stages.  The stop bar may be set back from the intersection to increase visibility between pedestrians and vehicles.  If there is adequate right-of-way, skewed intersections may be reconstructed as a roundabout. Refer to Section 4.4.13 for more information on pedestrian accommodations at roundabouts.

 California Department of Transportation, Complete Intersections: A Guide to Reconstructing Intersections and Interchanges for Bicyclists and Pedestrians (latest edition)  FHWA, Alternative Intersections/Interchanges: Informational Report (latest edition)  FHWA, MUTCD (latest edition)

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Traffic Signal Operations for Pedestrian Mobility - Contents

Traffic Signal Operations for Pedestrian Mobility - Contents ...... 5-i 5.1 Signal Timing Strategies for Pedestrians ...... 5-1 5.1.1 Pedestrian Recall ...... 5-1 5.1.2 Leading Pedestrian Interval ...... 5-2 5.1.3 Pedestrian Scramble ...... 5-3 5.1.4 Shorter Vehicular Cycle Lengths ...... 5-4 5.2 Pedestrian Infrastructure at Traffic Signals ...... 5-5 5.2.1 Pedestrian Detection Devices ...... 5-5 5.2.2 Accessible Pedestrian Signals and Detectors ...... 5-6 5.3 Traffic Control Devices for Uncontrolled Pedestrian Crossing Locations ...... 5-7 5.3.1 Rectangular Rapid Flashing Beacon ...... 5-7 5.3.2 Pedestrian Hybrid Beacons ...... 5-9

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Traffic Signal Operations for Pedestrian Mobility

Traffic operations practitioners should consider the needs and vulnerabilities of pedestrians when developing traffic signal timing plans. This chapter provides guidance on traffic signal timing strategies that improve accessibility, reduce pedestrian delay, and give more priority to pedestrians crossing the street. Historically, traffic signal timing has been primarily focused on automobile efficiencies, with less regard for the delay to pedestrians. Mitigation measures for pedestrian delay should be considered for urban core or urban areas, where there are high volumes of pedestrians.

“The traffic signal timing and optimization models we use continue to focus only on automobile traffic. These legacy signal timing policies at intersections have prioritized vehicle movements, leading to large and sometime unnecessary delays for pedestrians. Because pedestrian trips are short, delays at signalized intersections can affect pedestrians disproportionately and are a key factor in pedestrian non-compliance.” – ITE Journal May 2018

5.1 Signal Timing Strategies for Pedestrians

5.1.1 Pedestrian Recall Signals programmed with pedestrian recall automatically provide the pedestrian phase for every cycle. The pedestrian recall parameter causes the controller to place a continuous call for pedestrian service without active or passive pedestrian detection. Signals programed with pedestrian recall are more accessible and accommodating to pedestrians with disabilities than signals that require pedestrians to physically push a button to receive the pedestrian phase. In addition, the consistent service reduces pedestrian delay and increases the convenience for pedestrians.

 Pedestrian recall should be programed into traffic signals in downtown urban core, urban, and rural town areas and around developments that generate large volumes of pedestrian activity, such as schools, educational institutions, transit stations, event stadiums, and medical centers.

 Pedestrian intervals and signal phases should comply with requirements in MUTCD Section 4E.06.  The clearance interval should be calculated using a walking speed of 3.5 feet per second or less (MUTCD Section 4E.06).

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 In areas with large volumes of pedestrian activity, such as schools, educational institutions, transit stations, event stadiums, and medical centers, the pedestrian clearance interval may be extended to accommodate large groups and pedestrians with disabilities, who may walk slower than 3.5 feet per second.  Signals with pedestrian recall do not require pedestrian pushbuttons to be installed.

 California Department of Transportation, Complete Intersections: A Guide to Reconstructing Intersections and Interchanges for Bicyclists and Pedestrians (latest edition)  FHWA, Alternative Intersections/Interchanges (latest edition)  FHWA, MUTCD (latest edition)

5.1.2 Leading Pedestrian Interval Leading pedestrian interval (LPI) is a portion of a phase within the traffic signal cycle that provides the walk indication to pedestrians prior to the onset of the concurrent vehicular green indication. This allows the pedestrian to begin moving into the crosswalk before a right-turning vehicle enters the crosswalk space. This strategy may be used to increase the visibility of a pedestrian to drivers and has been shown to reduce conflicts between pedestrians and turning vehicles. If an LPI is provided without accessible signal features, pedestrians who are visually impaired may begin crossing at the onset of the vehicular movement when drivers are not expecting them to begin crossing.

“Leading Pedestrian Interval has been shown to reduce pedestrian-vehicle collisions as much as 60% at treated intersections.” - NACTO

 LPIs should be incorporated into traffic phasing sequences at intersections with a high volume of pedestrians and right- and left-turning vehicles.  LPIs are useful at T-intersections, where drivers on the side-street approach do not yield to oncoming traffic.

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 LPIs should provide pedestrians with a minimum lead of 3 seconds and should be timed to allow pedestrians to cross at least one lane of traffic or, in the case of a large corner radius, to travel far enough for pedestrians to establish their position ahead of the right-turning vehicle, before the right-turning vehicle is released (MUTCD Section 4E.06).  An advanced WALK signal should be displayed while red indications continue to be displayed to parallel through or turning traffic.  LPIs should be made accessible to visually impaired pedestrians. Refer to Section 5.2 for more information on accessible pedestrian signals.

 At intersections with a shared use path or bike infrastructure, a leading bicycle interval may be provided along with the LPI to reduce bicycle-vehicle conflicts.  Curb extensions may be used in combination with leading pedestrian intervals to improve the visibility between pedestrians and turning vehicles and to shorten the crossing distance. Refer to Section 4.4.2 for more information.  “No Turn on Red” (R10-11) prohibitions may be considered during the LPI.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  FHWA, MUTCD (latest edition)  GDOT, Design Policy Manual (latest edition)

5.1.3 Pedestrian Scramble The pedestrian scramble, also known as an all-WALK phase, is an exclusive pedestrian phase in which pedestrians may use lateral and diagonal crossings in an intersection while vehicle traffic is stopped. This strategy has been shown to reduce conflicts between pedestrians and turning vehicles.

 Pedestrian scrambles may be implemented at intersections with large volumes of pedestrian crossings.  Pedestrian scrambles may be implemented at intersections with a large number of conflicts or near misses between pedestrians and right- and left-turning vehicles.

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 During the pedestrian scramble phase, all vehicle approaches should be stopped.  Right turn on red should be prohibited during the exclusive pedestrian phase.  If a pedestrian scramble is incorporated into the signal cycle, it must be provided consistently while the traffic signal is in normal operating mode. The signal cannot switch between an all- WALK phase, where pedestrians may cross diagonally, and a typical pedestrian signal, where pedestrians may only cross in the direction parallel to moving traffic. This is to maintain pedestrian and vehicle expectancy. While the pedestrian scramble must be provided consistently, there is flexibility as to the number of times it may be provided during a cycle, and the length of the phase.

 A best practice is to monitor pedestrian compliance and delay after the installation of the pedestrian scramble.  The frequency and length of the pedestrian scramble phase may change in response to varying pedestrian and vehicle demand. For example, the pedestrian scramble may service the pedestrian phase once per cycle during peak vehicle hours and twice per cycle during peak pedestrian hours.  Pedestrian scrambles may service the pedestrian phase twice per signal cycle to reduce pedestrian delay compared to one scramble phase per cycle and may improve pedestrian compliance at the intersection.

5.1.4 Shorter Vehicular Cycle Lengths Pedestrians may experience a disproportionate amount of delay at intersections due to long traffic signal cycles that are designed to optimize vehicle movements. Traffic signals with excessively long signal cycles may provoke pedestrians to cross the street during a conflicting signal phase, increasing the potential for pedestrian-motor vehicle conflicts. Research indicates that pedestrians stop watching for the signal to change, and instead start looking for gaps to cross streets, when the average pedestrian delay exceeds 30 seconds. The length of time that a pedestrian is willing to wait for the WALK indication is a function of the type of roadway and traffic conditions. Shorter signal cycles may help reduce pedestrian delay at intersections and may be applied during non-peak and peak periods of traffic. In a coordinated traffic signal system, an example of a short Rev 3.0 5. Traffic Signal Operations for Pedestrian Mobility 4/25/19 Page 5-4 Pedestrian and Streetscape Guide

signal cycle is for an intersection to operate two cycles in the time that the traffic signal system operates a long cycle, which is commonly referred to as half cycles.

“Research has shown that in general, shorter cycle lengths benefit pedestrians leading to lower delay. The provision of shorter cycle lengths has also been recommended to encourage signal compliance and increase efficiency.” – ITE Journal May 2018

5.2 Pedestrian Infrastructure at Traffic Signals

5.2.1 Pedestrian Detection Devices Pedestrian detection devices inform the traffic signal of the presence of a pedestrian and cue the signal to provide the WALK signal in the next possible phase. The most common form of pedestrian detection is the pedestrian pushbutton, which is an active detection device. A pushbutton requires the pedestrian to physically push a button to receive the WALK signal. Alternatively, a passive pedestrian detection device identifies the presence of a pedestrian through infrared or video- processing technology without requiring action from the pedestrian.

 Pedestrian pushbutton assemblies should be installed at signalized intersections where pedestrian recall is not used (in which the pedestrian phase is programmed to be provided automatically). Pedestrian recall is preferred in locations with moderate to large pedestrian volumes, including urban, urban core, and rural town contexts and near land uses that generate high pedestrian volumes.  When used, pedestrian pushbutton assemblies should be installed on both ends of a crosswalk at signalized intersections and mid-block crossing locations with pedestrian signals, PHBs, or RRFBs.  When used, pedestrian pushbutton assemblies should be provided in pedestrian refuge areas at locations with a two-stage pedestrian crossing and where pedestrians might not be able to cross the street in one traffic signal phase.  Passive detection devices may be used in conjunction with a pedestrian pushbutton to identify the presence of pedestrians waiting on the sidewalk or in the crosswalk, and activate the traffic signal to provide, extend, and/or hold the pedestrian WALK phase.

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 A pedestrian pushbutton assembly should be mounted on a traffic signal pole or on a free- standing pole.  The pole on which the pedestrian pushbutton is mounted should not block the pedestrian access route or curb ramp.  Pedestrian pushbuttons should be located no more than 5 feet from the edge of the curb ramp (MUTCD Section 4E.08).  Pedestrian pushbuttons should be offset 1.5 to 6 feet from the edge of the curb, shoulder, or pavement (MUTCD Section 4E.08).  Pedestrian pushbuttons should be mounted 3.5 to 4 feet above the pavement (MUTCD Section 4E.08).  Pedestrian pushbuttons should be mounted such that it is clear which crosswalk is associated with the pushbutton operation.  Pedestrian pushbuttons should be mounted such that a person in a wheelchair at the top of a curb ramp may access the button.

 The traffic signal operation may be programmed to provide automatic pedestrian phase service, even if pedestrian detection is present.  If the traffic signal controller is enabled for detector diagnostics, the MaxView Detector Diagnostics reports, and Automated Traffic Signal Performance Measures may help identify pedestrian pushbutton failures and are useful maintenance tools.  Passive pedestrian detection may be used to detect pedestrians in the crosswalk and extend the pedestrian phase.  Passive pedestrian detection may be useful in areas where it has been observed that pedestrians do not use the pushbutton.

5.2.2 Accessible Pedestrian Signals and Detectors An accessible pedestrian signal and detector is an integrated device that uses visual or audible methods to communicate information about WALK and DON’T WALK intervals to pedestrians. Such

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methods include audible tones, speech messages, and vibrational surfaces. These types of signals may help visually impaired pedestrians navigate an intersection.

 Accessible pedestrian signals and detectors may be installed at signalized intersections and mid-block locations with a traffic signal, RRFB, or PHB traffic control device.  While PROWAG states that accessible pedestrian signals and detectors should be installed at pedestrian crossings where pedestrian signals are provided (PROWAG R209.1), MUTCD does not require that they be provided. Instead, MUTCD recommends that an engineering study be conducted to determine the need for an accessible pedestrian signal and detector.  Accessible pedestrian signals and detectors may be installed at intersections with large volumes of pedestrian activity, such as intersections within one-half mile of transit stations and medical centers or upon request from community members.

 The information provided by an accessible pedestrian signal should clearly indicate which pedestrian crossing is served by each device.  The information provided by an accessible pedestrian signal should not be limited in operation by time of day or day of week.  The design should comply with standards outlined in MUTCD Sections 4E.09 to 4E.13.

 Detectors may be active (pushbutton) or passive detection devices.

5.3 Traffic Control Devices for Uncontrolled Pedestrian Crossing Locations

5.3.1 Rectangular Rapid Flashing Beacon RRFBs are actuated flashing lights installed at a crosswalk with pedestrian crossing signs. RRFBs draw the driver’s attention to the crosswalk and communicate the presence of a pedestrian and the

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need to yield. An engineering study should be performed prior to installation that includes site-specific conditions. The guidance provided in this section may be used to guide the engineering study.

 RRFBs may be installed at uncontrolled pedestrian crossing locations (intersections or mid-block).  RRFBs may be installed on streets with a speed limit of 35 mph or less.  RRFBs may be installed on two-way streets with three or fewer lanes in each

direction.  RRFBs may be installed on one-way streets with three or fewer lanes.

 RRFB assemblies should be installed on the left and right sides of the roadway at the crosswalk.  If an RRFB is installed on a two-way street with a pedestrian refuge area, an additional RRFB assembly should be mounted in the median.  If an RRFB is installed on a multi-lane crossing without a pedestrian refuge area, an additional RRFB assembly should be mounted over the travel lane for each approach.  If an RRFB is installed on a three-lane crossing with or without a pedestrian refuge area, an additional RRFB assembly should be mounted over the travel center lane for each approach.  The beacon should be mounted below the standard crosswalk or school crosswalk warning signs, including W11-2 (Pedestrian), S1-1 (School), and W11-15 (Shared use trail crossing), and above the diagonal downward arrow (W16-7p) plaque (MUTCD Interim Approval 21).  Pushbuttons should be located in accordance with the guidance in Section 5.2.

 Pedestrian refuge areas may be installed along with the RRFBs to break up the crossing distance.  RRFBs may be installed at pedestrian crossings at roundabouts to increase the driver’s awareness of a pedestrian crossing.  RRFBs may be a lower cost alternative to traffic signals or PHBs.  Depending on the environment, RRFBs may create a false sense of security for pedestrians. In some cases, a median refuge area may provide the most significant safety benefit for the pedestrian.

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Figure 5.1. Rectangular Rapid Flashing Beacon

5.3.2 Pedestrian Hybrid Beacons A PHB, also known as a high-intensity activated crosswalk, is a traffic-control device used to stop vehicles at uncontrolled mid-block pedestrian crossing locations. An engineering study should be Rev 3.0 5. Traffic Signal Operations for Pedestrian Mobility 4/25/19 Page 5-9 Pedestrian and Streetscape Guide

performed prior to installation that includes site-specific conditions; the guidance provided in this section may be used to guide the engineering study.

 PHBs may be installed at uncontrolled mid-block pedestrian crossing locations (MUTCD Chapter 4F).  PHBs may be installed on streets with a speed limit of 45 mph or less.

 PHBs may be installed on two-way streets with four or fewer lanes in each direction.  PHBs may be installed on one-way streets with four or fewer lanes.  Refer to MUTCD Chapter 4F for pedestrian and vehicular volume thresholds that warrant the installation of a PHB.

 The PHB should be designed in accordance with MUTCD Chapter 4F.02.  If PHBs are installed on two-way streets with more than one lane in each direction, a pedestrian refuge area should be installed between opposing travel lanes.  A PHB indication should be installed over each active through lane.  Pushbuttons should be located in accordance with the guidance in Section 5.2.

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 Pedestrian refuge areas designed with a zigzag cut through may be installed in conjunction with PHBs to break up the crossing distance and to encourage pedestrians to face oncoming traffic before crossing the street. Refer to Section 4.3.7 of this Guide for more information on design of pedestrian refuge areas.  Consideration should be made to ensure standing water does not collect within the pedestrian refuge median or in front of the ADA ramps.  On two-way streets with a pedestrian refuge area, PHB faces may be installed in the median in addition to either side of the crosswalk.  PHBs may be installed at pedestrian crossings at two-lane roundabouts to increase the driver’s awareness of a pedestrian crossing.  PHB signals may be coordinated with adjacent traffic signals or in free operation. Pedestrians are more likely to be compliant with the signal if PHB is in free operation.  For applications that cross a two-way roadway, PHBs may provide the WALK phase in one or two stages.  Depending on the environment, PHBs may create a false sense of security for pedestrians. In some cases, a median refuge area may provide the most significant safety benefit for the pedestrian.

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Figure 5.2. Examples of Pedestrian Hybrid Beacons

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Streetscape Design for Pedestrian - Contents

Streetscape Design for Pedestrian - Contents ...... 6-i 6.1 Utilities ...... 6-2 6.2 Sidewalk Zones ...... 6-3 6.2.1 Frontage Zone ...... 6-4 6.2.2 Pedestrian Circulation Zone ...... 6-5 6.2.3 Greenscape/Furniture Zone ...... 6-7 6.3 Components of a Streetscape/Urban Design Elements ...... 6-10 6.3.1 Hardscape ...... 6-10 6.3.1.1 Concrete ...... 6-11 6.3.1.2 Asphalt...... 6-11 6.3.1.3 Bricks and Pavers ...... 6-11 6.3.2 Bike Parking ...... 6-11 6.3.3 Bollards ...... 6-16 6.3.4 Pedestrian-Scale Lighting ...... 6-17 6.3.5 Seating ...... 6-20 6.3.6 Transit Stop Amenities ...... 6-22 6.3.7 Trash Receptacles ...... 6-26 6.3.8 Wayfinding Signage ...... 6-27 6.4 Green Stormwater Infrastructure ...... 6-31 6.4.1 Bioretention Planters ...... 6-33 6.4.2 Biofiltration Planters ...... 6-34 6.4.3 Grassed Swales ...... 6-34 6.4.4 Permeable Pavement ...... 6-34 6.5 Tree and Plant Considerations ...... 6-36 6.5.1 Tree and Plant Selection ...... 6-36 6.5.2 Hardiness Zones of Georgia ...... 6-38 6.5.3 Infrastructure for Healthy Root Systems ...... 6-39 6.5.3.1 Open Tree Trenches ...... 6-40 6.5.3.2 Covered Tree Trenches ...... 6-40 6.5.4 Horizontal Clearances for Trees and Shrubs ...... 6-41 6.5.5 Tree and Plant Approval Prior to Installation ...... 6-43 6.5.6 Tree Protection during Construction ...... 6-43

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Streetscape Design for Pedestrian

Beyond transportation, streets are public spaces where people gather, play, dine, exercise, and conduct business. To create a space where people are comfortable and enjoy walking, designers should go beyond the minimum standards for pedestrian accommodations. Thoughtful selection and placement of hardscape materials, wayfinding signage, lighting, seating, and trees may create a pedestrian-friendly street within the public right-of-way. Since pedestrians are vulnerable to severe crashes, providing a network that supports pedestrian safety is paramount for all people, regardless of disabilities or age. This chapter provides guidance on the placement and design of streetscape components to improve

accessibility and enhance the safety, comfort, and character of a Figure 6.1. Streetscape, Atlanta, Georgia sidewalk. While most of content in this chapter applies to streets with curb and gutter, guidance on plantings and trees may be applied to all roadways. Prior to embarking on any streetscape project, the practitioner should carefully evaluate the context of the project, the speed of the street, and the primary intent of the project. Additionally, an essential component of all streetscape projects is the lateral offset to a fixed object, such as to lighting, benches, trees, bollards, trash receptacles, etc. The GDOT standard minimum lateral offsets to obstructions are listed later in this chapter. However, the reader is cautioned that the offsets alone do not present a complete solution to allow features or objects on the shoulder or roadside. Sound engineering judgment and reasonable environmental flexibility should be exercised in selecting and specifying roadside safety features at each location.

“Streets themselves are critical public spaces that can lend richness to the social, civic, and economic fabric of our communities.” – Project for Public Spaces

“From town parades and trick-or-treating, to markets and public gatherings, [streets are] where we celebrate and come together with our neighbors.” – Project for Public Spaces

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6.1 Utilities Utilities are often the most difficult element within a streetscape design project to coordinate and work with and around. It is essential that coordination with utility providers happens early and often and must be conducted throughout the project process. In some cases, sub-surface utility engineering (SUE) is required to determine the vertical and horizontal location of existing utilities. In other cases, a call to 811 to field locate the utilities may be sufficient, in conjunction with utilizing a registered surveyor, to develop accurate design plans that accommodate utilities. In all cases, utilities should be addressed at the onset of a streetscape, pedestrian improvement, or roadway project. Utility installations are governed by the GDOT Utility Accommodation Policy and Standards Manual. Designers should read and understand the referenced policy, in conjunction with the policies and guidelines set forth in the GDOT Design Policy Manual.

 No utility obstacle shall encroach on sidewalk clearances required by PROWAG.  Interruptions to pedestrian travel should be minimized, and construction should avoid damage to pedestrian facilities.  Lateral offsets to utility obstacles are measured from the face of curb to the face of pole or obstacle.  The utility provider should be contacted to relocate the existing utilities within the guidelines provided by GDOT’s Utility Accommodation Policy and Standards.

 For existing and proposed overhead utilities, the ideal option is to locate or relocate the utility underground; however, this option is often not financially feasible.  The poles and utility wires should be consolidated to minimize redundant lines and poles.

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6.2 Sidewalk Zones Creating a street that provides a comfortable environment for pedestrians requires going beyond minimum sidewalk infrastructure requirements, such as a 5-foot-wide sidewalk. While the addition of streetscape components may enhance the pedestrian-friendly character of a street, they may also obstruct access and create tripping hazards if not planned for carefully. To provide a functional and inviting pedestrian route, designers should conceptualize the sidewalk as a composition of three zones. Dividing the sidewalk into zones will help practitioners and designers organize streetscape components and result in adequate space for the intended activities. The three sidewalk zones discussed in this section are the frontage zone, pedestrian circulation zone, and greenscape/furniture zone. Although there is no physical boundary between these zones, each area has an optimal range of widths, as depicted on Figure 6.2, to accommodate a mix of streetscape components. The width of each zone varies based on the pedestrian activity, adjacent building uses, roadway and traffic characteristics, and desired character.

Figure 6.2. Sidewalk Zones

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6.2.1 Frontage Zone The frontage zone is the space connecting the adjacent property line to the pedestrian access route. Adjacent property use influences the type of activities that occur in the frontage zone and, in turn, the width and organization of streetscape components in this zone. For example, if the adjacent buildings are restaurants and shops, the frontage zone should be wide enough to accommodate outdoor café seating or storefront displays. Not all streetscapes have frontage zones but is a best practice to provide them especially if buildings and doors or adjacent to the sidewalk. Frontage zones are also great spaces for outdoor dining opportunities along a streetscape when ample space is provided.

 The frontage zone should be sufficiently wide to accommodate building door movements, and adequate space so that objects do not obstruct pedestrian circulation, including signs and seating.  Objects mounted to buildings that are lower than 80 inches above the surface of the sidewalk should not protrude more than 4 inches into the pedestrian circulation path (PROWAG R402).  Signs mounted in the frontage zone should be installed a minimum of 7 feet above the surface of the sidewalk (MUTCD Section 2A.18).  If the frontage zone connects to a building entrance, the hardscape surface material should be smooth, firm, stable, and slip resistant, and comply with PROWAG R302.7. Refer to Section 6.3.1 of this Guide for more information on ADA-compliant hardscape materials.

 When a sidewalk abuts a building that generates a large volume of pedestrian activity, such as restaurants, shops, and transit stations, the frontage zone may be extended to provide adequate space for benches, outdoor restaurant seating, plantings, merchandise displays, portable signs, and awnings.  The recommended width of the frontage zone to accommodate restaurant seating is 6 feet.  When a sidewalk is adjacent to a parking lot , trees and plants may be planted in the frontage zone to provide shade and a buffer between the expanse of asphalt and the sidewalk.  The minimum width of the frontage zone to accommodate trees is 4 feet.

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Figure 6.3. Example of a Frontage Zone (using planter boxes to protect door movements), Norcross, Georgia

6.2.2 Pedestrian Circulation Zone The pedestrian circulation zone is the portion of the sidewalk reserved for pedestrian travel. Like the frontage zone, the width of the pedestrian circulation zone should respond to the existing or anticipated volume of pedestrian activity. Areas with high volumes of pedestrian activity should be sized to accommodate the amount of anticipated pedestrian activity, rather than minimum requirements.

Figure 6.4. Examples of Pedestrian Circulation Zone

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 The minimum width of the pedestrian circulation zone is 5 feet (GDOT Design Policy Manual). Larger widths may accommodate higher volumes of pedestrians.  The longitudinal slope (or grade) of the pedestrian circulation zone should not exceed the grade established for the adjacent street or roadway. In cases where the sidewalk alignment deviates from the adjacent roadway, the longitudinal slope of the sidewalk should not exceed 5 percent (GDOT Design Policy Manual).  The maximum cross-slope for the pedestrian circulation zone is 2 percent (GDOT Design Policy Manual).  The hardscape materials in the pedestrian circulation zone should be smooth, firm, stable, and slip resistant, and comply with PROWAG R302.7. Refer to Section 6.3.1 of this Guide for more information related to hardscape materials and surfaces.  The pedestrian circulation zone should be clear of obstructions.

 When a sidewalk is adjacent to developments that generate a large volume of pedestrian activity, such as restaurants, shops, and transit stations, the recommended width is 8 to 12 feet. (NACTO Urban Street Design Guide: Sidewalks).  Relocation of fixed objects, such as utility poles, light fixtures, and other street furniture, should not impinge on or restrict the adjacent walkway. Walkways must be clear of fixed objects in coordination with ADA accessibility guidelines (NACTO Urban Street Design Guide: Sidewalks).  When a sidewalk crosses a commercial driveway, the driveway may be raised to the level of the sidewalk and the sidewalk hardscape material continued across the driveway. This driveway crossing design is similar to a raised crosswalk. For more information on raised crosswalks and driveway crossings, refer to Sections 4.4.11 and 0 of this Guide, respectively.  Sidewalk design should go beyond the bare minimum in both width and amenities. Pedestrians and businesses thrive where sidewalks have been designed at an appropriate scale, with sufficient lighting, shade, and street-level activity. These considerations are especially important for streets with higher traffic speeds and volumes, where pedestrians may otherwise feel unsafe and avoid walking.

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6.2.3 Greenscape/Furniture Zone The greenscape/furniture zone is the space between the pedestrian circulation path and the curb. This zone serves as a buffer between pedestrians on the sidewalk and vehicles on the street, and is reserved for signs, light and utility poles, seating, bicycle parking, transit stops, trash receptacles, trees, plants, and green stormwater infrastructure. The streetscape components in this zone should maximize safety, comfort, and function for all users. The width of the greenscape/furniture zone should respond to traffic speeds on the adjacent road, as well as the desired street furniture, amenities, and street trees and landscaping proposed for the zone.

 The greenscape/furniture zone should increase in width as the speed limit of the adjacent street increases.  On streets with speed limits 35 mph or greater, the greenscape/furniture zone should be a minimum of 5 feet wide.  The minimum width of the greenscape/furniture zone varies depending upon the streetscape components placed in this zone:  If the greenscape/furniture zone is reserved for only light poles and utilities, the zone should be a minimum of 2 feet wide (FHWA Designing Sidewalks and Trails for Access).  If planting trees or placing bike parking in the greenscape/furniture zone, the zone should be a minimum of 4 feet wide (FHWA Designing Sidewalks and Trails for Access). For more information on trees, plantings, and stormwater infrastructure in this zone, refer to Sections 6.4 and 6.5 of this Guide.  If providing seating in the greenscape/furniture zone, the zone should be a minimum of 6 feet wide, with fixed objects set back a minimum of 4 feet from the face of curb for low speed streets of 35 mph or less.  If the sidewalk is adjacent to a transit stop, refer to Sections 4.3.12 and 6.3.6 of this Guide for more information on the design of transit stops.  Objects placed in the greenscape/furniture zone should not extend into and obstruct the pedestrian circulation zone.

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Figure 6.5. Example of Pedestrian Circulation Zone with a Frontage and Furniture Zone, Norcross, Georgia

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Figure 6.7. Dimensions of Greenscape/Furniture Zone with Tree on a low speed street of 35 mph or less located Figure 6.6. Example of Greenscape Zone within a Central Business District

Figure 6.8. Examples of Greenscape/Furniture Zones

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6.3 Components of a Streetscape/Urban Design Elements Streetscapes are complex and are made up of many components that may change based on context and pedestrian activity. Components of a streetscape, often referred to as urban design elements, are typically confined to the urban shoulder of a street on lower speed streets, 35 mph or less and include but are not limited to elements such as hardscape materials, planters, tree grates, benches, trash receptacles, bike racks, kiosk, wayfinding signage, pedestrian scale lighting, bollards, and green infrastructure systems to treat the first 1 inch of stormwater runoff.

6.3.1 Hardscape A variety of hardscape materials may be used to introduce color and texture to the sidewalk and enhance the character of a place. While using a variety of hardscape materials is encouraged, the surfaces used for pedestrian circulation areas should be smooth, firm, stable, and slip resistant, and comply with PROWAG Section R302.7. Quality control issues may be avoided by requesting the contractor prepare a mock-up of materials such as walls, specialty hardscape features, and stone work during the preconstruction phase, potentially saving time and money. The primary hardscape materials used in sidewalks are concrete, asphalt, brick, concrete, and stone pavers. Concrete and asphalt are the primary materials for shared use paths. This section provides information on where materials may be applied, and considerations for installing and maintaining the hardscape surface.

Figure 6.9. Example of Sidewalk with Multiple Materials

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6.3.1.1 Concrete Concrete is the preferred hardscape material for sidewalks because it provides a smooth, durable finish and is easy to grade. Colored and textured concrete, such as a sand-blasted finish, may be used as accents in the frontage and greenscape/furniture zone. A primary challenge with concrete surfaces is avoiding the development of cracks that will maintain ADA compliance. To comply with ADA, cracks that are 1/2-inch-wide or greater should be patched, and vertical displacements 1/4 inch or greater should be grinded or cut down. While cracks are a normal part of concrete aging, well-designed saw cuts or joints may minimize crack sizes over time and control where cracks occur. 6.3.1.2 Asphalt Asphalt provides a smooth surface and may be used for shared use paths and for sidewalks in rural areas. While asphalt is less expensive than concrete, it is typically not as long lasting. Asphalt sidewalks and paths should be maintained to ADA standards. 6.3.1.3 Bricks and Pavers Bricks and pavers may be used to introduce texture, color, and patterns into the sidewalk. These hardscape materials may be used in historic districts and plazas, and as accents in the frontage and greenscape/furniture zones. Brick and paver hardscapes may be designed with aggregate and sand joints to allow water to permeate the surface. While bricks and pavers may provide environmental and aesthetic benefits, maintaining a level surface and controlling the spacing between units are challenges. Transitions between unit pavers, tree grates, concrete panels, and pedestrian circulation zones should be given special attention to minimize gaps and bumps that may be caused by settlement. A contractor with experience in unit paver installation should be selected to install bricks and pavers. Bricks and pavers that are proposed within a local road or street, should be placed on a bituminous setting bed in a herringbone pattern. When using bricks or pavers within a street, the designer should consult further with the brick or paver manufacturer for the exact specifications as each project has specific criteria that should be evaluated on a project by project basis. Bricks and pavers are not permitted to be used within the street or roadway on a State Route or “On System” facility.

 FHWA, A Guide for Maintaining Pedestrian Facilities for Enhanced Safety (latest edition)  NACTO, Urban Street Design Guide (latest edition)

6.3.2 Bike Parking Providing adequate and appropriate bike parking is essential to supporting and encouraging bicycling as a viable transportation option. The two primary factors that determine the usefulness of bike parking are location and type. This section provides guidance on the placement and installation of bike parking, as well as recommendations for selecting the type of bike parking.

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 Bike parking may be provided at common destinations, such as transit stops, grocery and convenience stores, schools, parks, main streets, and town centers.  Bike parking may be placed in the frontage and greenscape/furniture zones.  In situations where sidewalk space is limited or where a high demand for bike parking exists, bicycle parking may be located on-street parking spaces. Eight to ten bike parking spaces may typically be provided in one on-street vehicle parking space.

 Bike parking should be placed in convenient and well-lit locations, close to entrances, and visible from the bike route or destination entrance.  A minimum clearance of 36 inches should be maintained on all sides of the bike rack, corral, station, or locker to prevent a parked bike from obstructing a travel path. Figure 6.10 illustrates the recommended offset dimensions for a typical U-rack.

 When deciding which type of bike parking is appropriate for a given location, the following may be considered: the anticipated number of users, the space available, the types of bikes being parked, and the length of use (short-term versus long-term). Common types of bike parking include bike racks, bike corrals, bike lockers, and bike shelters. There are variations within each type. For more information on the types of bike parking, refer to further guidance in this section.  If there is not enough space to accommodate bike parking in one area, dispersed U-racks or repurposing an on-street vehicle parking space for bike parking may be considered.  A variety of bike parking types may be needed to accommodate all bicycle shapes and sizes. The footprint of a standard bicycle is approximately 6 feet by 2 feet, but cargo bicycles and bicycles with trailers have a larger footprint and may require additional space.  To accommodate long-term bike storage, bike shelters or bike lockers may be installed.  If designing custom bike racks, verify that a bicycle may be locked to it with a standard U-lock.

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 AASHTO, Guide for the Development of Bicycle Facilities (latest edition)  APBP, Essentials of Bicycle Parking (latest edition)  City of Boston , Boston Complete Streets Design Guidelines (latest edition)  Dero, Commercial Bike Racks (latest edition)  FHWA, Bicycle and Pedestrian Program (latest edition)  Mayor’s Office of Transportation and Utilities, Philadelphia Complete Streets Design Handbook (latest edition)  NACTO, Bike Share Station Siting Guide (latest edition)  NACTO, Transit Street Design Guide: Bike Parking (latest edition)  NACTO, Urban Bikeway Design Guide (latest edition)  Reliance Foundry, The Essential Guide to Bike Parking (latest edition)  San Francisco Municipal Transportation Agency, Bicycle Parking: Standards, Guidelines, Recommendations (latest edition)

Figure 6.10. Offset Dimensions for U-Rack Bike Parking Placed Perpendicular to the Curb

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Figure 6.11. Offset Dimensions for U-Rack Bike Parking Placed Parallel to the Curb

Figure 6.12. Offset Dimensions of Bike Corral

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Figure 6.13. Example of Bike Parking in the Figure 6.14. Example of Bike Parking in On- Amenity Zone Street Parking Space

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6.3.3 Bollards Bollards are vertical objects that come in rigid, semi-rigid, or flexible varieties. They are used create temporary or permanent separation between components of the streetscape or modes of transportation. Using a context sensitive design approach or utilizing a municipality’s streetscape design guideline if available, bollards may be a component of the street that adds character to the place while providing a separation without creating an impermeable barrier.

 Bollards highlight traffic calming measures and, depending on how frequently they are placed, protect pedestrians, bicyclists, landscape plantings, and buildings by discouraging unauthorized vehicles from encroaching into the pedestrian circulation zone.

 The minimum height for bollards is 30 inches.  Bollards should be visible in all lighting conditions for all users and marked with brightly colored reflective paint or emblems to contrast from the surrounding environment.  Bollards may be lighted to provide supplemental illumination for a pedestrian facility.  Bollard lighting may be solar powered.  Bollards may be movable, flexible, semi-flexible, or fixed.  Bollards may be spaced with a minimum distance of 5 feet apart, which provides sufficient space for pedestrians and bicyclists to move through but does not allow for the passage of vehicles.  Proper spacing should consider the balance of restricting vehicles with the requirement of providing an unobstructed pedestrian circulation zone.  Bollards should not be an obstruction for people with disabilities.  Sight distance should allow users to adjust their speed, especially on paths that have traffic calming features installed.  Bollards may be used to keep pedestrians from stepping off the curb in areas other than the crosswalk.  Bollards require maintenance due to deterioration or crashes.

 City of Boston, Boston Complete Streets Design Guidelines (latest edition)  FHWA, Pedestrian & Bicycle Safety (latest edition)  FHWA, MUTCD (latest edition)

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Figure 6.15. Example of Bollards Figure 6.16. Example of Flexible Bollards

6.3.4 Pedestrian-Scale Lighting Pedestrian-scale lighting serves the essential function of illuminating sidewalks, crosswalks, and bike lanes, and has been shown to reduce crashes in urban and suburban areas where there is a concentration of pedestrians (AASHTO Green Book Section 3.6.3). The increased sense of safety and security allows pedestrians to feel more comfortable walking at night.

 Pedestrian-scale lighting may be provided at intersections and street corridors with pedestrian infrastructure.  Pedestrian-scale lighting may be provided at controlled or uncontrolled mid-block crossing locations.  Pedestrian-scale lighting may be provided along bridges, tunnels, and pedestrian over- and underpasses.  Pedestrian-scale lighting may be provided at transit stop locations.  Pedestrian-scale lighting should be provided in places with high volumes of pedestrian activity, such as transit stations, medical centers, educational institutions, and downtown urban areas.

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 Lighting at mid-block pedestrian crossings should be placed 10 feet in front of the crosswalk, from the driver’s perspective (FHWA Informational Report on Lighting Design for Midblock Crosswalks).  Lighting should provide 20 vertical lux at the crosswalk (FHWA Informational Report on Lighting Design for Midblock Crosswalks).  When a pedestrian crossing is placed on roads with two-way traffic or roads wider than 44 feet, lighting should be provided on both sides of the crosswalk (FHWA Informational Report on Lighting Design for Midblock Crosswalks).  Pedestrian light standards should be located at the back of the sidewalk. If sidewalk is not present, the light standards should be placed a minimum of 6 feet from the face of curb.  Pedestrian-scale lighting should be less than or equal to 20 feet above the surface of the sidewalk.

 Lighting may be placed in the frontage or greenscape/furniture zone.  The placement of trees should be coordinated with the proposed and existing pedestrian lighting so as not to create areas of shadow, reducing visibility on sidewalks.  When selecting the type of lighting, energy-efficient options, fixture spacing, the shade of white color, and alternative power sources may be considered.  A best management practice of utilizing LED lights should be considered to reduce maintenance and provide energy savings.

 AASHTO, Roadside Design Guide (latest edition)  AASHTO, Roadway Lighting Design Guide (latest edition)  European Committee for Standardization  FHWA, Lighting Handbook (latest edition)  GDOT, Design Policy Manual (latest edition)  GDOT, Lighting Design Process (n.d.)  Illuminating Engineering Society of North America (latest edition)  International Commission on Illumination (latest edition)  International Dark-Sky Association (latest edition)

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Figure 6.17. Pedestrian-Scale Lighting, Atlanta, Georgia

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6.3.5 Seating Opportunities to sit down and rest are necessary for pedestrians with mobility impairments and older adults. Seating also invites people to spend time in a place and socialize, bringing life to the street. Many forms of seating, such as benches, movable chairs, and seat walls, may be incorporated into a streetscape design. This section provides guidance on the placement of seating as it relates to the pedestrian circulation zone. This section does not provide recommendations for selecting the type of seating.

 Seating should not block fire hydrants, pushbutton assemblies, access to transit, or loading zones.  Benches and other forms of seating should be placed a minimum of 5 feet from the back of the curb to accommodate wheelchair access.  Benches and other forms of seating should be offset a minimum of 1.5 feet from the edge of the pedestrian circulation zone to ensure they do not obstruct pedestrian access.  To accommodate wheelchair access, a 30 inch by 48-inch clear space should be provided adjacent to seating.

 Seating may be fixed or mobile.  Seating may be integrated with other streetscape components, such as raised planting beds and low concrete walls.  When placing seating, the view from the seat should be considered. It is often desirable to place seating to face the property adjacent to the street, and in others it might be necessary for the seating to face the street, such as at transit stops.  It is often desirable to provide seating adjacent to trees or in a shaded area.  When placing seating near other fixed objects, maintenance and trash removal needs to be considered. Seating may be offset a minimum of 1 foot from fixed objects for maintenance needs.

 City of Boston, Boston Complete Streets Design Guidelines (latest edition)  Mayor’s Office of Transportation and Utilities, Philadelphia Complete Streets Design Handbook (latest edition)  NACTO, Transit Street Design Guide: Seating (latest edition)  US Access Board, PROWAG (latest edition)

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Figure 6.18. Seating Placement

Figure 6.19. Example of Seating, Atlanta, Georgia Rev 3.0 6. Streetscape Design for Pedestrians 4/25/19 Page 6-21 Pedestrian and Streetscape Guide

6.3.6 Transit Stop Amenities Amenities at transit stops such as signs, maps, benches, lighting, trash receptacles, bike racks, and shelters may improve accessibility, visibility, comfort, and convenience for pedestrians taking transit. When installing amenities at transit stops, it is important to consider how pedestrians will access transit vehicles and how non-transit riders will navigate around the transit stop. This section provides guidance on how to place amenities at transit stops while maintaining accessibility for all users. This section also provides recommendations for when to consider providing certain amenities. For more information on the placement of transit stops along a corridor and design specifications for bus bulb- outs and pullouts, refer to Section 4.3.12.

 Transit accommodations may be provided in both urban and rural areas where pedestrians often rely on transit as their primary mode of transportation.  Transit shelters may be provided in neighborhoods where buses run infrequently, in urban areas with high level of ridership, and in areas where there are many older adults or persons with disabilities.

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 Transit stops should be ADA-compliant and accessible for all users.  Amenities at transit stops should be installed considering the relationship to the adjacent sidewalk and transit boarding. Amenities at transit stops should not be placed in or protrude into the pedestrian circulation zone or the transit loading zone. Transit amenities include, but are not limited to, signs, maps, benches, light posts, kiosks, trash receptacles, and shelters.  A 5-foot-long (parallel to the curb) by 8-foot-deep (perpendicular to the curb) loading zone should be provided at all transit stops.  The loading zone should be kept clear to provide ample space for bus door operations, wheelchair lifts, and pedestrians waiting and queuing for transit. Sufficient space should be provided such that pedestrians waiting at the stop do not obstruct the pedestrian access route. The amount of space varies based on the type and ridership levels of the transit, and the available width of the sidewalk.  Benches, light posts, kiosks, trash receptacles, and shelters should be set back a minimum of 4 feet (3 feet minimum) from the curb.  Transit stop signs may be placed within 1 foot of the curb.  The bottom of transit stop signs should be at least 7 feet and no more than 10 feet from the surface of the pavement.  Bus shelters should be offset 3 feet from the loading zone, 10 feet from fire hydrants, and 1 foot from fixed objects.  Local transit agencies should be consulted to verify local requirements for loading zones, bus stop locations, and other design criteria that may be unique to individual transit authorities.  Amenities in or around transit shelters should be stable, durable, and vandal resistant.

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 The placement of a transit shelter is decided on a case-by-case basis. Pedestrian facilities adjacent to and near transit stops should be planned and designed collaboratively among the transit agencies, public works, and traffic engineering departments of the local jurisdiction.  Benches, trash cans, and lighting may be incorporated at transit stops.  Accessibility should be provided with ramps, detectable warning features, and clearly defined and delineated pedestrian spaces.  If the sidewalk is not wide enough to support a 5-foot-by-8-foot loading zone, a bus bulb-out may be installed. Refer to Section 4.3.12 for guidance on the design of bus bulb-outs.  Well-lit and active accessways leading to transit facilities may be provided to increase security.  Travel information keeps riders updated with schedules, routes, and real-time arrival and departure times. Local maps and wayfinding information should be provided to keep riders informed. Refer to Section 6.3.8 for more information.  When determining appropriate transit stop or shelter placement, the location of utilities should be considered.  A regularly scheduled maintenance plan should be used for bus stops and shelters.  Shade awnings, trees, seating, and bicycle racks may be placed in the vicinity of transit stops to accommodate intermodal transfers and improve pedestrian comfort.  Shelters should be located to facilitate maintenance.  Additional passenger amenities such as seating, local area information, wayfinding, and real- time traveler information should be considered concurrent with shelters.

 AASHTO, A Policy on Geometric Design of Highways and Streets (latest edition)  City of Boston, Boston Complete Streets Design Guidelines (latest edition)  ITE, Designing Walkable Urban Thoroughfares (latest edition)  Mayor’s Office of Transportation and Utilities, City of Philadelphia Green Streets Design Manual (latest edition)  NACTO, Transit Street Design Guide: System Wayfinding & Brand (latest edition)

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Figure 6.20. Standard Transit Stop

Figure 6.21. Transit Shelter Dimensions

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Figure 6.22. Example Transit Shelter Figure 6.23. Transit Shelter Wayfinding

6.3.7 Trash Receptacles Strategically located trash receptacles are convenient to use and help keep streetscapes clean.

 Trash receptacles may be located near high-pedestrian activity areas, such as near transit amenities or commercial areas.  Trash receptacles may be placed in the frontage or greenscape/furniture zone.

 Trash receptacles should be located for pedestrian convenience and accessibility.  Trash receptacles should not block or protrude into the pedestrian circulation zone.  Trash receptacles (including animal waste bag dispensers and containers) should be easy to maintain and empty.  The quantity of trash receptacles required on a site is based on the volume of people who use the area, the frequency of maintenance, sanitation schedules, and the amount of litter generated.

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 Additional Considerations

 When selecting materials for trash receptacles, the durability of materials should be considered.  The local municipality should be contacted to determine whether streetscape standards for urban design elements have already been established.

Figure 6.24. Site Elements – Bench, Trash Receptacle

6.3.8 Wayfinding Signage Wayfinding signage is an essential component of pedestrian-friendly streetscapes that assist pedestrians with navigating an area. Wayfinding signage may be used to orient and provide directions to pedestrians, especially when they are in unfamiliar areas. Wayfinding signage is more flexible than regulatory signage in terms of design and placement. (Regulatory signage is used to inform users of traffic laws and to draw attention to pedestrian or bike facilities, and is governed by the FHWA

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MUTCD.) While there are many types of signs that contribute to the complex character of streets, this section focuses on wayfinding signage.

 Wayfinding signage may be used to direct pedestrians to destinations such as transit stops and stations, schools, parks, recreational facilities, libraries, cultural points, museums, entertainment centers, shops, business districts, neighborhoods, and bike route connections.  Wayfinding signage may be used as part of a gateway treatment to identify the entrance to a place.  Wayfinding signage may be used as a part of placemaking.  Wayfinding signage may be placed in the frontage or greenscape/furniture zone, on furniture, on building facades, or in/on the pavement.

 Wayfinding signage should be placed at key decision points along pedestrian and bike routes and at origins and destinations. Decision points are where the pedestrian or cyclists must decide whether to continue along the route or change direction.  Wayfinding signs should be offset a minimum of 1 foot from the curb (4 feet preferred).  Wayfinding signs should not be placed in or protrude into the pedestrian circulation zone, except for pavement decals.  Pavement decals should not be thicker than ¼ inch to comply with ADA and so as not to create a tripping hazard and shall not have a joint or opening exceeding ½ inch.  Signage should be mounted 7 feet above the surface of the sidewalk.  Wayfinding signage should be durable and designed to withstand harsh weather conditions.

 Wayfinding signage may take many forms; some examples include kiosks, maps, sidewalk or pavement decals, plaques embedded in the ground, or engravings.  Wayfinding signage may be designed with simple phrases and graphics that are easy to interpret.  A best practice is providing wayfinding signage that includes a reference point on a map—such as a symbol or the phrase ‘You Are Here’—to help pedestrians orient themselves, as does signage that includes distances in the form of average walking or biking time.

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 City of Boston, Boston Complete Streets Design Guidelines (latest edition)  Designworkplan, “Introduction to Wayfinding and Signage design” (n.d.)  FHWA, MUTCD (latest edition)  Foltz, Designing Navigable Information Spaces (latest edition)  GDOT, Signing and Marking Design Guidelines (latest edition)  Illuminating Engineering Society of North America (latest edition)  NACTO, Transit Street Design Guide: System Wayfinding & Brand (latest edition)  NACTO, Urban Bikeway Design Guide (latest edition)

Figure 6.25. Example of Wayfinding Signage

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Figure 6.26. Example of Wayfinding Signage, Midtown, Atlanta

Figure 6.27. Example of Placemaking with Banners and Sculpture

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6.4 Green Stormwater Infrastructure Green stormwater infrastructure refers to natural systems of plant, soil, and rock used to treat and reduce stormwater runoff from impervious surfaces at the source or where the rainfall lands. Since streets and sidewalks make up a large percentage of the impervious surfaces in the public right-of- way, green infrastructure should be considered as a first line of defense in treating stormwater quality. In addition, integrating green infrastructure best management practices into streetscape designs may reduce the volume of stormwater flowing into regional detention systems. Green infrastructure techniques are often the most effective when used in combination with conventional storm drainage systems such as inlets and pipes as they are typically only effective in treating the first 1 to 1.2-inch rainfall event. GDOT-owned roads or streets that transect a municipal separate storm sewer system (MS4) area must incorporate green infrastructure into the project. Refer to Figure 6.30 at the beginning of a project to check whether the project is in an MS4 area. For more information on the requirements of MS4, refer to GDOT Drainage Design for Highways Chapter 10. GDOT’s Drainage Design for Highways and ARC’s Georgia Stormwater Management Manual are the two statewide resources for additional detailed information on green stormwater management best practices. Drainage Design for Highways provides a list of GDOT green infrastructure applications pre-approved for use on GDOT-owned and operated facilities. This section provides high-level guidance for a few post-construction stormwater best management practices and green infrastructure types that may be adapted for urban areas and incorporated into streetscape designs.

Figure 6.28. Example of Green Infrastructure, Decatur, Georgia

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Figure 6.29. Example of Green Stormwater Infrastructure, Decatur, Georgia

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Source: GDOT, Stormwater MS4 Management Program Blue represent the MS4 Permitted areas

Figure 6.30. Map of MS4 Permitted Areas in Georgia Below is a list of some best management practices, or BMPs, for “green infrastructure”. Please note not all BMPs are applicable for State Routes or “On System” facilities. Further engineering evaluation along with a detailed hydrology study should be conducted prior to the implementation of any stormwater BMP.

6.4.1 Bioretention Planters A bioretention planter is a plant, soil, and rock infiltration and filtration system suitable for small drainage areas with a high percentage of impervious surfaces. Bioretention planters are bioretention basins with a vertical wall around the edges. Bioretention planters may be incorporated into the frontage or greenscape/furniture zone, curb extensions, and medians of pedestrian refuge areas. The planter depth, width, and vegetation type should be determined based on the results of a detailed hydrology study determining stormwater loads and site constraints. Bioretention planters should be sized to handle the runoff load of the tributary areas and drain within a minimum of 72 hours. Bioretention planters should be a minimum of 4 feet wide to maximize performance. Bioretention

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Planters are best used in urbanized areas with limited Right-Of-Way are not permitted on State Routes or “On System Facilities”.

6.4.2 Biofiltration Planters A biofiltration planter is a plant, soil, and rock filtration system suitable for areas where infiltration cannot be achieved. The design of biofiltration planters follows the same requirements as bioretention planters, except that stormwater is stored and slowly released into a subsurface perforated pipe and carried to the grey stormwater infrastructure instead of infiltrating into the subgrade soil. The size and width of a biofiltration planter should be determined based on the results of a detailed hydrology study determining stormwater loads and site constraints. Biofiltration Planters are best used in urbanized areas with limited Right-Of-Way are not permitted on State Routes or “On System Facilities”.

6.4.3 Grassed Swales A grassed swale is similar to a bioretention planter, but without the walls around the edges. Grassed swales are shallow depressions with sloped slides. Bioretention swales require more space than planters to accommodate the optimal slope. Grassed swales are more appropriate when Right-Of- Way is more available as it requires more space implement. Grassed swale Best Manager Practices are permitted on State Routes or “On System” facilities.

6.4.4 Permeable Pavement Permeable pavements are alternative pavement surfaces that allow stormwater to seep through the hardscape material or joints to the subsurface, rather than using traditional stormwater drain systems. Common types of permeable pavements include porous asphalt, pervious concrete, and permeable pavers or bricks. Permeable pavements are laid on top of an infiltration bed and subgrade soil to trap and filter pollutants. Permeable pavement may be used as hardscape accents in the frontage or greenscape/furniture zones. When incorporating permeable pavement into streetscapes, regular maintenance requirements should be considered to vacuum out the sediment which collects in the hardscape voids and blocks infiltration. Permeable pavements are not suitable for roads or streets with high volumes of truck traffic or on facilities with grades that exceed a 5” slope. An application that may be more suitable for permeable paving for consideration would be parking spaces, again further engineering evaluation should be conducted prior to utilizing permeable pavers as a stormwater BMP.

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Figure 6.31. Illustration of Permeable Pavement

 ARC, Georgia Stormwater Management Manual (latest edition)  GDOT, Drainage Design for Highways (latest edition)  GDOT, Stormwater System Inspection and Maintenance Manual (latest edition)  Liptan and Santen, Sustainable Stormwater Management: A Landscape Driven Approach to Planning and Design (latest edition)  NACTO, Urban Street Design Guide (latest edition)  NACTO, Urban Street Stormwater Guide (latest edition)  Slaney, Stormwater Management for Sustainable Environments (latest edition)

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6.5 Tree and Plant Considerations Trees and plants should be incorporated into streetscape designs as much as possible to achieve the following benefits: improve air and water quality, reduce stormwater runoff and soil erosion, increase biodiversity in metropolitan areas, and provide shade and cooling for pedestrians. Tree and plants may be incorporated into the frontage and greenscape/furniture zones and within curb extensions and should comply with the specifications outlined in GDOT Policy 6755-9, Policy for Landscaping and Enhancements on GDOT Right of Way. While trees and plants have numerous benefits for pedestrians, they may also create maintenance challenges. This section provides guidance on factors to consider helping mitigate maintenance issues related to street trees and plantings.

 Street trees are best planted between the sidewalk and edge of pavement on streets with speeds of 35 mph and less.

6.5.1 Tree and Plant Selection It is important to select the right tree and plants for a site to ensure longevity and to minimize conflicts with adjacent infrastructure. Trees and plants should be selected based on the specific hardiness zone and the micro climate conditions for a site, including sun/shade conditions, soil compaction, water availability, size of a proposed planting area, and soil volume. In addition, the designer should evaluate specific existing and proposed site conditions associated with the site, which include, but are not limited to, posted speed limits, existing and proposed underground and overheard utilities, site distances at intersections, approaching traffic signal locations, existing and proposed underground and overhead utilities, site aspect (north, south, east, west facing), slopes, tree availability, and existing building and tree locations within the project area. These criteria will help determine the most appropriate tree and tree size for the project site location. The full mature size of the proposed tree should be factored into selection, as the placement of the tree could compromise lateral offset requirements and site distances to traffic signals, signs and from intersections. Trees should be limbed up 80 inches above the adjacent grade to provide clear visibility. When selecting trees, designers should refer to the list of suggested trees below and the current edition of American Standard for Nursery Stock (AmericanHort latest edition) and GDOT Policy 6755- 9, Policy for Landscaping and Enhancements on GDOT Right of Way for invasive plants that are not permitted on the state’s rights-of-way.

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Partial Tree Selection List Small Canopy: 15 to 20 feet tall with a spread of 15 to 30 feet wide Amelanchier arborea | Downey Serviceberry Crataegus phaenopyrum | Washington Hawthorn Cercis canadensis | Eastern Redbud Koelreuteria paniculata | Golden Rain Tree Chionanthus virginicus | White Fringe Tree Lagerstroemia indica | Crepe-Myrtle Cornus florida | Flowering Dogwood Prunus x yedoensis | Yoshino Cherry Medium Canopy: 35 to 40 feet tall with a spread of 25 to 35 feet wide Acer buergerianum | Trident Maple Metasequoia glyptostroboides | Dawn Redwood Acer ginnala | Amur Maple Nyssa ogeche | Ogeechee Lime, Ogeechee Tupelo Acer rubrum | Red Maple Nyssa sylvatica | Black tupelo Carpinus betulus | European Hornbeam Oxydendrum arboretum | Sourwood Carpinus caroliniana | American Hornbeam Pistacia chinensis | Chinese Pistache Cercidiphyllum japonicum | Katsura Tree Platanus x acerifolia | London Plane tree Cladrastis kentukea | American Yellowwood Prunus caroliniana | Carolina Cherry laurel Cupressus arizonica | Arizona (Carolina Saphire) Taxodium distichum | Bald cypress Cypress Ulmus parvifolia | Chinese (Athena, Bosque, etc.) Juniperus virginiana | Eastern Redcedar Elm Magnolia virginiana | Sweetbay Magnolia Ulmus americana ‘Jefferson’ | Jefferson Elm Large Canopy: 40 to 80 feet tall with a spread of 30 to 40 feet wide Acer rubrum 'Autumn Blaze' | Autumn Blaze Maple Quercus phellos | Willow Oak Fraxinus americana | White Ash Quercus prinus | Chestnut Oak Ginkgo biloba | Ginkgo (male variety only) Quercus rubra | Northern Red Oak Liquidambar styraciflua 'Rotundiloba' | Sweet Gum Quercus shumardii | Shumard Oak Platanus × acerifolia | London Planetree Quercus stellate | Post Oak Quercus alba | White Oak Quercus texana | Nuttal Oak Quercus coccinea | Scarlet Oak Quercus virginiana | Live Oak Quercus falcate | Southern Red Oak Sabal palmetto | Palmetto Palm Quercus hemisphaerica | Laurel Oak Ulmus americana 'Princeton' | American Elm Quercus lyrata | Overcup Oak

Table 6-1. Partial Tree Selection List

 AmericanHort, American Standard for Nursery Stock (latest edition)  GDOT Policy 6755-9, Policy for Landscaping and Enhancements on GDOT Right of Way  GDOT, Design Policy Manual (latest edition)  University of Georgia Extension Service, Shade and Street Tree Care (latest edition)

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Figure 6.32. Shade Trees along a Street, Dunwoody, Georgia

6.5.2 Hardiness Zones of Georgia Hardiness zones should be used to determine what type of plants may be installed at the location where a streetscape project is being constructed. According to the United States Department of Agriculture, hardiness zones are geographic regions used to determine which plants are most likely to thrive at a specific location. The identification of trees and plants is based on average annual- minimum winter-temperature and climatic conditions. Using plants that are appropriate for the hardiness zone will ensure that they survive through different seasons.

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Figure 6.33. Map of USDA Hardiness Zones in Georgia

6.5.3 Infrastructure for Healthy Root Systems The health and longevity of a tree is related to soil volume available for root growth as the tree matures. Table 6-2 provides the minimum and optimal width of planting strips, tree spacing, and soil volumes for small, medium, and large trees. These dimensions should be met to accommodate root flare and minimize future damage to the sidewalk.

Table 6-2. Street Tree Planting and Soil Area Dimensions

Small Canopy Trees Medium Canopy Trees Large Canopy Trees Mature Height of Tree 15 ft to 20 ft 35 ft to 40 ft 40 ft to 80 ft Planting Strip Width 4 ft 6 ft 8 ft Spacing Between Trees 20 ft recommended 30-40 ft recommended 40-50 ft recommended 15 ft minimum 25 ft minimum 30 ft’ minimum Minimum Soil Volume 120 ft3 per tree 500 ft3 per tree 1,000 ft3 per tree preferred

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Figure 6.34. Recommended Soil Volumes

Trees should not be planted in spaces less than 4 feet wide as this will hinder the development of a tree’s crown and roots. Tree trenches may be used to provide the appropriate soil volumes in limited urban environments. Tree trenches are continuous basins filled with soil that run parallel to the street. 6.5.3.1 Open Tree Trenches In an open tree trench the soil around the base of the tree is exposed. These may be used in areas where pedestrians are not likely to walk on and damage the tree. For example, open tree trenches may be appropriate for a center median, but may not be appropriate for a street with curbside parking and retail, due to the volume of pedestrian traffic that is likely to walk across the tree trench. 6.5.3.2 Covered Tree Trenches Covered tree trenches use a support system to suspend pavement over the soil in the trench. The pavement covering should protect the soil from compaction caused by excessive foot traffic and, in some cases, vehicles use for periodic maintenance. Examples of structural supports include structural cells, rock-based structural soil, sand-based structural soil, and soil boxes.

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Figure 6.35. Example of Covered Tree Trench

6.5.4 Horizontal Clearances for Trees and Shrubs The clearance zone is located adjacent to active lanes of vehicle traffic, and the width of the clearance zone is a function of the design speed of the roadway. The clearance zone requirements impact the placement and size of trees and shrubs located near the street. Figure 6.36 is from GDOT’s Design Policy Manual and provides the minimum horizontal clearance for trees and shrubs related to roadway posted design speeds and context. The minimum horizontal clearance, also referred to the lateral horizontal offset, is between the location of a proposed tree or landscape element measured from the adjacent edge of pavement or face of curb to the center of the tree trunk or plant. For “on system” and state route roadways, trees and shrubs within the horizontal clear zone should be limited to a maximum height of 30 inches. For “off system” streets under the jurisdiction of local agencies refer to local ordinances that may apply. If local ordinances do not exist, refer to GDOT’s Design Policy Manual for horizontal clearances for trees and shrubs.

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Figure 6.36. GDOT Chart - Horizontal Clearance for Trees and Shrubs

Deviation from the requirements for “on system” streets shall be approved by GDOT in writing through the design variance process (see Chapter 2). Refer to GDOT Policy 6755-9, Policy for Landscaping and Enhancements on GDOT Right of Way for further guidance on landscape enhancements on state rights-of-way. For “off system” streets under the jurisdiction of a local agency, refer to local design standards if available. Street trees within medians and in pedestrian traffic areas should be pruned so that the limbs are a minimum of 7 feet above grade. Utilities and intersection sight distance requirements may affect the location of proposed trees in the horizontal clear zone. Additional requirements for clearance setbacks are provided by GDOT’s Design Policy Manual. Within a streetscape setting, large mature trees should be pruned to provide a minimum of 80 inches of clear visibility and should be maintained to not obstruct traffic signals or traffic signs. Prior to proposing a tree or plant material for a project, the practitioner must become familiar with the existing and proposed site conditions. Careful consideration should be made to determine the appropriate tree for the given context. The practitioner should evaluate the mature size of the proposed tree or plant so that essential elements such as traffic signals and signs are not blocked by the proposed tree or plant. A conservative approach is best for determining the right tree or plant for a location so that safety measures are not impacted by the installed landscape element.

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For example, a Live Oak could be planted 4 feet from the face of curb to the center of the tree trunk within the horizontal clear zone on a low speed street of 35 mph or less within a Central Business District. However, the Live Oak’s growth habit and size at maturity may result in an encroachment on the travel lane during its life, and therefore should be either set back further or replaced with a more suitable tree with a smaller size at maturity. In this case, the tree may suffer due to the limited soil volume, the sidewalk could be undermined and lifted, and roadway elements such as the curb and roadway base could be impacted. Countermeasures such as “root panels” may help mitigate the root system, however over time, the Live Oak roots will overcome the panels due to the root growth habit.

6.5.5 Tree and Plant Approval Prior to Installation The project landscape architect should be retained by the client to tag trees and approve plant material at the nursery, prior to shipping or transporting items to the project site. The landscape architect should verify the specified design intent and quality is achieved. In some instances, it may not be practical to send the landscape architect to the nursery; in those cases, at a minimum, the landscape contractor should provide the landscape architect with pictures of the landscape material with a measuring tape or measuring rod to verify the height and form of the tree for review, comment, and final approval.

6.5.6 Tree Protection during Construction Soil compaction is the number one reason trees die as part of streetscape projects. Trees should be protected from soil compaction to mitigate damage that occurs to soil structure due to construction activities. Soil compaction from heavy construction equipment reduces the soil’s capability to hold and absorb water, impedes and stunts root growth, increases runoff, and severely impacts the health of the tree. When a tree is within the project limits and there is a risk of construction activity occurring around the root zone of a tree that is to be saved, it should be included in the tree protection zone or (TPZ). The TPZ zone extends to the far ends of the tree canopy. The Figure 6.37. Tree Selection at a Nursery critical root zone (CRZ) is measured from the center of the tree, for every 1 inch of diameter of tree or caliper, extend the radius 1 foot out to the entire diameter of the existing tree. For example, a 36 inch diameter or caliper tree trunk will have a 36 foot radius CRZ. Whichever is further, the TPZ or the CRZ, is where to start the tree protection or orange barrier fencing and encircle the existing tree. Another option for protecting the tree roots of an existing tree is to place 6 inches of gravel underneath the sidewalk or pavers to minimize soil compaction over the root system. This is an effective and low

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cost method to provide additional benefits to the environment during and after a streetscape project is completed.

Figure 6.38. Tree Root Protection to Minimize Compaction

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Figure 6.39. Tree Protection During Construction Table 6-3 provides guidance on how to monitor trees during different phases of construction to ensure that the Critical Root Zone, or CRZ, is not damaged by soil compaction.

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Table 6-3. Monitoring Trees During Construction

Survey Phase

 The surveyor should locate specimen trees, typically determined by the local municipality within their tree protection ordinance, within the project limits, noting at minimum the location, species, and caliper inches.  Surveyor should review the local tree ordinances to ensure that the survey picks of existing trees that meet the local tree ordinance as related to replacement and recompense requirements.  Site boundaries, required zoning, easements, and environmental setbacks should be marked on survey plans.  A tree inventory should include the location, size, and relative health of each tree.

Planning Phase

 Location and integration of long-term tree protection and site design should be discussed with the client and project team.  Assessment of existing utilities should be made to identify any conflicts between future street trees and existing utilities.

Design Phase

 Coordination between utility providers and street tree locations should be coordinated and approved by project team and utility providers.  Trees to be preserved onsite should be determined and trees should be conserved in groups where possible.

Pre-construction Phase

 Contractor ingress and egress of the project site should be discussed. The contractor’s equipment and parking should be outside the fenced TPZ.  Potential laydown areas of soil/construction material and proximity to tree protection fencing should be discussed prior to construction.  Durable tree protection fencing (orange barrier or chain link fence as specified) should be placed to restrict entry into the TPZ in the construction zone.  Weatherproof signage should be placed along the tree protection barrier, at 6- to-8-foot intervals, stating “KEEP OUT TREE PROTECTION AREA.”  Prior to construction activities, branches or trees that may pose an immediate risk to people or structures should be removed.  Soil health and past site damage should be surveyed, sampled, and assessed.  Each stage of construction should be photo documented.

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Construction Phase

 Maintenance staff should be engaged in early decision making, and educated about the care of retained and proposed trees and their requirements for protection during construction.  TPZs should not be disturbed during construction activities.  If roots 2 inches or greater in diameter are exposed outside of the CRZ, contractors should use root wrap to further aerate and hydrate roots as feasible.

Site Monitoring

 Tree protection barriers should be kept until the project is completed.  Contractor should inspect the TPZ a minimum of once per week to ensure fencing is compliant and intact. Contractor should correct fencing if damaged or unlocked.

Post-Construction Phase

 TPZ fencing may be removed.  A final inspection should be performed. Mulch thickness and soil moisture should be monitored. Tree damage should be assessed and inspected for insects and pests, and fertilization if needed.

 Dines and Brown, Time-Saver Standards for Landscape Architects (latest edition)  FHWA, A Guide for Maintaining Pedestrian Facilities for Enhanced Safety (latest edition)  GDOT, Design Policy Manual (latest edition)  ISA, Managing Trees During Construction (latest edition)  University of Florida, Landscape Plants (latest edition)  Urban, Up by Roots: Healthy Soils and Trees in the Built Environment (latest edition)

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Pedestrian Safety in Work Zones - Contents

Pedestrian Safety in Work Zones - Contents ...... 7-i 7.1 Temporary Traffic Control and Detour Plans ...... 7-1 7.2 Components of an Accessible Work Zone ...... 7-3 7.2.1 Separation Devices ...... 7-3 7.2.2 Sidewalk Closure and Detour Signs ...... 7-3 7.2.3 Temporary Pedestrian Crossings ...... 7-4 7.2.4 Temporary Pedestrian Walkways ...... 7-4 7.3 Maintenance of Pedestrian and Bicycle Infrastructure in Work Zones ...... 7-6

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Pedestrian Safety in Work Zones

The most common interruptions impacting the sidewalk are work zones from development-related construction projects, roadway and streetscape construction projects, and utility work in the public right-of-way, which may last for months or even years. Work zones may be particularly challenging for pedestrians, introducing unfamiliar conditions, confusion, noise, delay, and the potential for conflicts with vehicles. When a work zone disrupts pedestrian travel through the partial or full closure of the sidewalk, a convenient and accessible alternative route must be provided, guiding the pedestrian around the work site and back to the original sidewalk or walkway. This chapter provides guidance on alternative routes for pedestrians in construction work zones.

7.1 Temporary Traffic Control and Detour Plans When roadway or development projects are in the planning phase, a plan should be developed to minimize pedestrian disruptions during construction. Temporary traffic control and detour plans should consider accessibility for pedestrians, bicyclists, and public transit. For further guidance, please refer, GDOT, Special Provision Section 150 – Traffic Control (latest edition)

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 Existing pedestrian facilities, including access to transit stops, should be maintained. Where pedestrian routes are closed, alternate routes should be provided.  Closures of existing, interim, and final pedestrian facilities should have the prior written approval of the Engineer, as specified in GDOT Special Provision Section 150.  Whenever a sidewalk is to be closed, the Engineer should notify the maintaining agency two weeks prior to the closure, as specified in GDOT Special Provision Section 150.  Prior to closure, barriers that are detectable by a person with a visual disability traveling with the aid of a long cane, as described by the MUTCD, should be placed across the full width of the closed sidewalk.  When existing pedestrian facilities are disrupted, closed, or relocated in a temporary traffic control zone, the temporary facilities should be detectable and should include accessibility features.  The alternative route should be located adjacent to the existing sidewalk where possible. Separation devices should be placed between the alternative route and the construction site, and between the alternative route and moving traffic.  The sidewalk should be fully closed on only one side of the street at a time.  Alternative pedestrian routes should be prioritized over parking and vehicle lanes.  Efforts should be made to keep transit stops operational, and pedestrian pathways to transit stops and boarding locations must remain clear.  Pedestrian detours and accommodations should not affect access to businesses during operating hours, and scaffolding and equipment must not block accessible electronic door opening panels. The agency or developer overseeing the project should consider the access needs of affected businesses and notify affected businesses and property owners.

Preferred prioritization for alternative pedestrian accommodations: 1. Separate the pedestrian walkway (or a portion thereof) from the work site with a separation device. 2. Create a temporary pedestrian walkway or shared use path in an adjacent parking lane and separate it from vehicle or bike traffic. 3. Create a temporary pedestrian walkway or shared use path in an existing bike lane adjacent to the sidewalk, separate it from vehicle traffic, and either merge bicycles with traffic or with pedestrians on a shared use path. 4. Create a temporary pedestrian walkway in an adjacent vehicle lane and separate it from vehicle traffic 5. Close the full sidewalk and detour the pedestrian across the street to the opposite sidewalk. 6. Close the full sidewalk and detour the pedestrian on a different route.

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Sidewalk closure should only be considered when no other solution is possible. When closure is required, work crews and utility construction should be coordinated to minimize pedestrian impacts and avoid peak times.

7.2 Components of an Accessible Work Zone Traffic control devices used during the construction of “on system” projects should meet the standards utilized in the MUTCD, and should comply with the requirements outlined in GDOT Special Provision Section 150, Georgia Construction Standards and Details, Project Plans, Design Manuals, and Special Provisions. All traffic control devices used during the construction of “off system” projects by local agencies should meet the standards utilized in the MUTCD and the project construction documents. The GDOT requirements should be considered to provide an accessible work zone consistent with the standard practice used on construction projects in Georgia, or better.

7.2.1 Separation Devices Temporary pedestrian walkways and shared use paths should have continuous physical separation from vehicular traffic (except at crosswalks) and active work zones.

 Barriers used along a temporary pedestrian route should comply with the MUTCD Section 6D.01-.02.  Barriers must be ADA detectable and highly visible with retroreflective markings.  Barriers with a hand rail should be between 34 inches and 42 inches high, allowing pedestrians to use the hand rail as a guide for their hands.  Separation devices may be barriers, fencing, or other stable, continuous, non-flexible channelization devices; caution tape and flexible fencing do not provide sufficient separation.

7.2.2 Sidewalk Closure and Detour Signs In the case of a sidewalk closure that requires a detour, advanced signage should be provided directing pedestrians to the detour. Clear signage should be provided at the nearest intersection and on both sides of a sidewalk or detour to alert pedestrians and guide them back to the original sidewalk.

 Sidewalk closure and detour signs should comply with GDOT Construction Detail T-21.  Sidewalk closure signs should be cane-detectable and extend across the width of the sidewalk.  Signage should not block the minimum pedestrian travel-way requirements.

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7.2.3 Temporary Pedestrian Crossings During construction near pedestrian crossings, advance signage should be placed at intersections to alert pedestrians of construction work sites that may be located at intersections or mid-block locations and direct them to safe alternate routes.

 Avoid closing crosswalks if possible. If a street crossing is closed, the crosswalk should be blocked with continuous Type II or Type III barriers. Pedestrian signal heads should be removed, covered, or turned, on both sides of the closed crosswalk, and sidewalk closure signage should be provided.  Where temporary signals need to be included in the traffic control plan, pedestrian phases should be included in the temporary signals.  Temporary marked crosswalks require an engineering study, and should meet crosswalk requirements in Section 4.4.8 of this Guide.  Parking should be restricted within 50 feet of a temporary mid-block crosswalk, and within 20 feet of a temporary marked crosswalk at a permanent crossing for increased visibility.  Where a temporary pedestrian walkway begins or ends at a crosswalk, temporary markings must be provided to align pedestrians with the legal crossing.  Where a temporary pedestrian walkway includes a crosswalk that remains open, a barrier should be provided to align pedestrians with the legal crossing.  The visibility of the pedestrian signal heads should be maintained from all points in the crosswalk.  Access to pedestrian pushbuttons should be maintained if possible. Otherwise, the signal must temporarily be changed to include an automatic pedestrian crossing phase.

7.2.4 Temporary Pedestrian Walkways During the construction of structures that are adjacent to sidewalks, a temporary covered walkway may be installed to protect pedestrians from falling debris. Temporary covered walkways should provide sufficient lighting for nighttime use, be designed to be robust and provide clear sight distances at intersections and crosswalks.

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 Pedestrian walkways should comply with GDOT Sidewalk Diversion Detail T-20.  Pedestrian walkways should be 5 feet wide (minimum 4 feet) for constrained areas.  Pedestrian walkways should meet PROWAG requirements, including width, slope, and cross slope requirements.  Grade changes greater than ½ inch must provide temporary ADA-compliant ramps.  Temporary multiuse paths should be a minimum of 8 feet wide in confined areas for a limited distance, if not the temporary shared use paths should be a minimum of 10 feet.  A 96-inch vertical clearance should be maintained along the length of a temporary shared use path.  Covered pedestrian walkaways should maintain an 80-inch vertical clearance to overhead obstructions.  Surface materials should be firm, stable, and slip resistant.

Figure 7.1. Example of Pedestrian Circulation Adjacent to a Construction Site Rev 3.0 7. Pedestrian Safety in Work Zones 4/25/19 Page 7-5 Pedestrian and Streetscape Guide

7.3 Maintenance of Pedestrian and Bicycle Infrastructure in Work Zones Pedestrian and bicycle facilities in and adjacent to work zones should be maintained to provide safety and functionality. Proper maintenance will maximize the safety, effectiveness, and life of work zone alternative routes or detour facilities. Inadequate maintenance activity may result in increased work zone accidents. The contractor should maintain existing and temporary traffic control devices as specified in the traffic control plan, and should have them routinely inspected by a knowledgeable person for adequate compliance, visibility, and condition of the traffic control devices. Local jurisdictions should train construction inspection staff to recognize improper and unsafe pedestrian facilities.

 Walkways and bike route surfaces should be inspected regularly and be free of construction debris, including gravel, dirt, or mud.  The contractor should inspect after storms for blown over construction signage, construction fencing, and barricades.  Pathways should remain clear and passable and free of obstacles such as parked equipment and vehicles, temporary storage of construction materials, traffic control signs, overhead or encroaching obstructions, and misaligned construction fencing.  Surfaces with holes, cracks, or vertical separation should be replaced.  Damaged or misaligned traffic barriers should be replaced or repositioned to be consistent with the traffic control plan.  If the pedestrian or bicycle route changes during construction, the detour signing should be inspected to ensure a clearly understood pathway.

 AASHTO, Guide for the Development of Bicycle Facilities (latest edition)  City of Chicago , Rules and Regulations for Construction in the Public Way (latest edition)  City of Portland, Traffic Design Manual Volume 2: Temporary Traffic Control (latest edition)  FHWA, MUTCD Section 6G.05 (latest edition)  GDOT, Special Provision Section 150 – Traffic Control (latest edition)  HDOT, Hawaii Pedestrian Toolbox Section 11: Safety in Work Zones and Maintenance (2013)  NACTO, Urban Street Design Guide: Curb Extensions (latest edition)  US Access Board, PROWAG (latest edition)

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References - Contents

References - Contents ...... 8-i

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AASHTO. 2004. Guide for the Planning, Design, and Operation of Pedestrian Facilities. American Association of State Highway and Transportation Officials. https://store.transportation.org/Item/CollectionDetail?ID=131 AASHTO. 2005. Roadway Lighting Design Guide. American Association of State Highway and Transportation Officials. https://store.transportation.org/Item/PublicationDetail?ID=1412 AASHTO. 2008. Guide Specifications for Design of FRP Pedestrian Bridges. American Association of State Highway and Transportation Officials. https://store.transportation.org/Item/CollectionDetail?ID=5&gclid=EAIaIQobChMIvOP-4u- I3gIVl8BkCh3HKAz2EAAYAiAAEgJ-XvD_BwE AASHTO. 2011. Roadside Design Guide. American Association of State Highway and Transportation Officials. https://store.transportation.org/Item/CollectionDetail?ID=105 AASHTO. 2012. Guide for the Development of Bicycle Facilities. American Association of State Highway and Transportation Officials. https://store.transportation.org/Item/CollectionDetail?ID=116 AASHTO. 2017. LRFD Bridge Design Specifications, 8th Edition. American Association of State Highway and Transportation Officials. https://store.transportation.org/Item/CollectionDetail?ID=152 AASHTO. 2018. A Policy on Geometric Design of Highways and Streets. Green Book. American Association of State Highway and Transportation Officials. https://store.transportation.org/Item/CollectionDetail/180?NoCategory AmericanHort. 2014. American Standard for Nursery Stock. https://cdn.ymaws.com/americanhort.site-ym.com/resource/collection/38ED7535-9C88- 45E5-AF44-01C26838AD0C/ANSI_Nursery_Stock_Standards_AmericanHort_2014.pdf APBP. 2015. Essentials of Bike Parking: Selecting and installing bicycle parking that works. Association of Pedestrian and Bicycle Professionals. September 2015. https://cdn.ymaws.com/www.apbp.org/resource/resmgr/Bicycle_Parking/EssentialsofBikePa rking_FINA.pdf ARC. 2016. Georgia Stormwater Management Manual. Prepared by AECOM, Atlanta Regional Commission, Center for Watershed Protection, Center Forward, Georgia Environmental Protection Division, and Mandel Design. https://cdn.atlantaregional.org/wp- content/uploads/2017/03/gsmm-2016-final.pdf ARC. 2016. Walk. Bike. Thrive! A regional vision for a more walkable, bikeable, and livable metropolitan Atlanta. Prepared by Alta Planning + Design. https://atlantaregional.org/plans- reports/bike-pedestrian-plan-walk-bike-thrive/ California Department of Transportation. 2010. Complete Intersections: A Guide to Reconstructing Intersections and Interchanges for Bicyclists and Pedestrians. https://nacto.org/docs/usdg/complete_intersections_caltrans.pdf

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FHWA. 2016. Road Diets/Roadway Reconfiguration. Federal Highway Administration. https://safety.fhwa.dot.gov/road_diets/ FHWA. 2017. Guide for Improving Pedestrian Safety at Uncontrolled Crossing Locations. FHWA- SA-17-072. Federal Highway Administration. https://www.fhwa.dot.gov/innovation/everydaycounts/edc_4/guide_to_improve_uncontrolled _crossings.pdf FHWA. 2017. Medians and Pedestrian Crossing Islands in Urban and Suburban Areas. FHWA-SA- 17-064. Federal Highway Administration. https://safety.fhwa.dot.gov/provencountermeasures/ped_medians/ FHWA. 2017. Rumble Strips and Stripes. https://safety.fhwa.dot.gov/roadway_dept/pavement/rumble_strips/bike_fs/ FHWA. 2017. Traffic Calming ePrimer. Federal Highway Administration. https://safety.fhwa.dot.gov/speedmgt/traffic_calm.cfm FHWA. 2018. Bicycle and Pedestrian Program. Federal Highway Administration. https://www.fhwa.dot.gov/environment/bicycle_pedestrian/ FHWA. 2018. Pedestrian & Bicycle Safety. Federal Highway Administration. https://safety.fhwa.dot.gov/ped_bike/ FHWA. n.d. State Best Practice Policy for Medians. FHWA-SA-11-019. https://safety.fhwa.dot.gov/ped_bike/tools_solve/fhwasa11019/fhwasa11019.pdf Foltz, Mark A. 1998. Designing Navigable Information Spaces. University of Leeds Department of Electrical Engineering and Computer Science. Thesis. http://www.ai.mit.edu/projects/infoarch/publications/mfoltz- thesis/node8.html#SECTION00817000000000000000 GDOT Construction Detail A-3. http://mydocs.dot.ga.gov/info/gdotpubs/ConstructionStandardsAndDetails/A-3_A-3.pdf GDOT Construction Detail A-4. http://mydocs.dot.ga.gov/info/gdotpubs/ConstructionStandardsAndDetails/A-4.pdf GDOT Construction Detail T-11A. http://mydocs.dot.ga.gov/info/gdotpubs/ConstructionStandardsAndDetails/T11A_T11a.pdf GDOT. 2008. Construction Detail T-21: Traffic Control Pedestrian Accessibility Around Work Zone- Sidewalk Detour. Georgia Department of Transportation. October 16, 2008. http://mydocs.dot.ga.gov/info/gdotpubs/ConstructionStandardsAndDetails/Forms/AllItems.as px GDOT. 2008. Sidewalk Diversion Detail T-20: Traffic Control Pedestrian Accessibility Around Work Zone-Sidewalk Diversion. Georgia Department of Transportation. October 16, 2008. http://mydocs.dot.ga.gov/info/gdotpubs/ConstructionStandardsAndDetails/Forms/AllItems.as px GDOT. 2010. Environmental Procedures Manual. Georgia Department of Transportation. July 2010. http://www.dot.ga.gov/PS/DesignManuals/EnvironmentalProcedures

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GDOT. 2011. Policy for Landscaping and Enhancements on GDOT Right of Way. Policy 6755-9. Georgia Department of Transportation. December 1, 2011. http://mydocs.dot.ga.gov/info/gdotpubs/Publications/6755-9.pdf GDOT. 2015. External Right of Way Manual. May 2015. http://www.dot.ga.gov/PartnerSmart/DesignManuals/ROW/00ExternalRightofWayManual.pdf GDOT. 2015. Stormwater System Inspection and Maintenance Manual. Prepared by ARCADIS U.S., Inc. for Georgia Department of Transportation. April 2015. http://www.dot.ga.gov/PartnerSmart/DesignManuals/Drainage/I%20and%20M%20Manual.p df GDOT. 2016. Context Sensitive Design Online Manual. Georgia Department of Transportation. December 2016. http://www.dot.ga.gov/PartnerSmart/DesignManuals/ContextSensitiveDesign/GDOT_CSD_ Manual.pdf GDOT. 2016. Local Administered Project (LAP) Manual. Georgia Department of Transportation. October 2016. http://www.dot.ga.gov/PartnerSmart/Local/Documents/LAPManual/Manual/LAPManual.pdf GDOT. 2016. Public Involvement Plan for NEPA Projects. Georgia Department of Transportation. http://www.dot.ga.gov/PartnerSmart/DesignManuals/Environmental/Public%20Involvement %20Plan/PublicInvolvementPlan.pdf GDOT. 2016. Regulations for Driveway and Encroachment Control. Georgia Department of Transportation. March 2016. http://www.dot.ga.gov/PartnerSmart/DesignManuals/Encroachment/Driveway.pdf GDOT. 2016. Utility Accommodation Policy and Standards. http://www.dot.ga.gov/PartnerSmart/utilities/Documents/2016_UAM.pdf GDOT. 2017. Intersection Control Evaluation (ICE) Policy. Georgia Department of Transportation. http://www.dot.ga.gov/PartnerSmart/DesignManuals/Intersection%20Control%20Evaluation/ ICE%20Policy.pdf GDOT. 2017. Plan Development Process. Georgia Department of Transportation. September 2017. http://www.dot.ga.gov/PartnerSmart/DesignManuals/PDP/PDP.pdf GDOT. 2017. Plan Presentation Guide. Georgia Department of Transportation. July 2017. http://www.dot.ga.gov/PartnerSmart/DesignManuals/Plan/Plan_Presentation_Guide.pdf GDOT. 2017. Special Provision, Section 150 – Traffic Control. February 2017. Georgia Department of Transportation. http://www.dot.ga.gov/PartnerSmart/Business/Source/special_provisions/shelf/sp150.pdf GDOT. 2018. Bridge and Structures Design Manual. August 2018. http://www.dot.ga.gov/PartnerSmart/DesignManuals/BridgeandStructure/GDOT_Bridge_and _Structures_Policy_Manual.pdf GDOT. 2018. Design Policy Manual. Georgia Department of Transportation. April 2018. http://www.dot.ga.gov/PartnerSmart/DesignManuals/DesignPolicy/GDOT-DPM.pdf

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NACTO. 2016. Bike Share Station Siting Guide. National Association of City Transportation Officials. https://nacto.org/wp-content/uploads/2016/04/NACTO-Bike-Share-Siting- Guide_FINAL.pdf NACTO. 2016. Global Street Design Guide. National Association of City Transportation Officials. October 2016. https://islandpress.org/book/global-street-design-guide NACTO. 2016. Transit Street Design Guide. National Association of City Transportation Officials. April 2016. https://nacto.org/publication/transit-street-design-guide/ NACTO. 2017. Urban Street Stormwater Guide. National Association of City Transportation Officials. June 2017. https://islandpress.org/books/urban-street-stormwater-guide National Safety Council. 2013. Near Miss Reporting Systems. https://www.nsc.org/Portals/0/Documents/WorkplaceTrainingDocuments/Near-Miss- Reporting-Systems.pdf NCDOT. 2015. North Carolina Pedestrian Crossing Guidance. July 2015. https://connect.ncdot.gov/resources/safety/Teppl/TEPPL%20All%20Documents%20Library/ Pedestrian_Crossing_Guidance.pdf PEDS. 2014. Safe Routes to Transit: Toolkits for Safe Crossings in Metro Atlanta. Pedestrians Educating Drivers on Safety. http://peds.org/wp-content/uploads/2014/06/4729-SR2T- toolkits_Final.pdf PEDS. 2016. Identifying, Assessing, and Improving Uncontrolled Intersections for Pedestrian Access. Pedestrians Educating Drivers on Safety. https://www.fhwa.dot.gov/innovation/everydaycounts/edc_4/guide_to_improve_uncontrolled _crossings.pdf Rails to Trails Conservancy. 2018. Tunnels and Underpasses. https://www.railstotrails.org/build- trails/trail-building-toolbox/design/tunnels-and-underpasses/ Reliance Foundry. 2018. The Essential Guide to Bike Parking: Site planning and installation for bike racks, lockups, and lockers. January 2018. https://www.reliance-foundry.com/blog/bike- parking-guide#gref San Francisco Municipal Transportation Agency. 2015. Bicycle Parking: Standards, Guidelines, Recommendations. San Francisco Municipal Transportation Agency. Created November 18, 2011. Updated December 3, 2015. https://www.sfmta.com/sites/default/files/reports-and- documents/2017/12/1_sfmta_bicycle_parking_guidelines-updated-01-17-2017.pdf Schroeder, Bastian. 2015. Observations of Pedestrian Behavior and Facilities at Diverging Diamond Interchanges. North Carolina State Institute of Transportation Research and Education. http://onlinepubs.trb.org/Onlinepubs/webinars/150819.pdf Slaney, S. 2016. Stormwater Management for Sustainable Environments. Australia : The Image Publishing Group Pty Ltd. Tefft, Brian C. 2013. “Impact Speed and a Pedestrian’s Risk of Severe Injury or Death.” Accident Analysis and Prevention. https://www.sciencedirect.com/science/article/abs/pii/S000145751200276X

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TRB. 2006. Improving Pedestrian Safety at Unsignalized Crossings. National Cooperative Highway Research Program Report 562. Transit Cooperative Research Program Report 112. https://nacto.org/wp-content/uploads/2010/08/NCHRP-562-Improving-Pedestrian-Safety-at- Unsignalized-Crossings.pdf TRB. 2010. NCHRP Report 672, Roundabouts: An Informational Guide– Second Edition. National Cooperative Highway Research Program. Transportation Research Board. Washington, D.C. https://nacto.org/docs/usdg/nchrprpt672.pdf University of Florida. 2015. Landscape Plants. Last Modified February 27, 2015. https://hort.ifas.ufl.edu/woody/appropriate-tree-pits.shtml University of Georgia. 2014. Shade and Street Tree Care. University of Georgia Extension Service. UGA Extension Bulletin 1031. http://extension.uga.edu/publications/detail.html?number=B1031&title=Shade%20and%20St reet%20Tree%20Care Urban, James. 2008. Up by Roots: Healthy Soils and Trees in the Built Environment. International Society of Arboriculture. http://www.jamesurban.net/up-by-roots/ US Access Board. 2011. Proposed Accessibility Guidelines for Pedestrian Facilities in the Public Right-of-Way. PROWAG. July 26, 2011. https://www.access- board.gov/attachments/article/743/nprm.pdf US Access Board. 2014. Detectable Warning Update. https://www.access-board.gov/guidelines- and-standards/streets-sidewalks/public-rights-of-way/guidance-and-research/detectable- warnings-update

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Appendix A. Mid-Block Pedestrian Crossing Evaluation

A.1 Introduction A.1.1 Goals of this Guide The goal of this guide is to assist engineers, planners, and other professionals in evaluating the placement of pedestrian crossings, and selecting traffic control and other design elements at uncontrolled locations. Uncontrolled pedestrian locations occur where a sidewalk or pedestrian path intersects a roadway at a location where no traffic control (i.e., stop sign or traffic signal) that requires a stop condition in advance of the pedestrian crossing. Pedestrians often desire to reach the opposite side of the roadway at more frequent intervals than crossing at existing signalized or stop controlled intersections permit. When deciding where to cross the street, pedestrians constantly judge whether their personal safety will be improved by walking to the nearest crosswalk versus crossing at a point outside of the marked crossing. In urban areas with large volumes of pedestrians and high crossing demand, a lack of pedestrian crossing opportunities can result in unsafe crossing behavior (PEDS, Identifying, Assessing, and Improving Uncontrolled Intersections for Pedestrian Access: Draft Recommendations). On the other hand, simply marking a crosswalk without including other pedestrian crossing treatments such as lighting, pedestrian hybrid beacons, curb extensions, etc., does not necessarily improve pedestrian safety. In some situations, the marked crosswalk alone may increase the potential for pedestrian-vehicle crashes. Before installing a marked crosswalk at an uncontrolled location, agencies should complete a pedestrian crossing evaluation. This guide outlines a step-by-step process and provides data collection worksheets to assist with the evaluation. This guide provides recommendations for situations where marked crosswalks:  May be installed  If placed alone are not sufficient  May be supplemented with additional traffic control and pedestrian safety infrastructure, such as lighting, curb extensions, a median refuge island, etc. A.1.2 Agency Application There are many factors to consider when deciding whether a marked pedestrian crossing is recommended at a specific location and what type of treatment is appropriate. Because every situation is unique, it is difficult to prescribe a “one size fits all” evaluation process. The evaluation process and criteria presented in this guide are GDOT’s guidance and recommendations. The final decision to install pedestrian crossing infrastructure is based on engineering judgment. A.1.2.1 Agency Feedback Developing a methodology that supports consistent evaluation and installation of pedestrian infrastructure is a collaborative effort that requires continuous feedback. The process described in this guide is continually evolving and becoming more refined as more emphasis is placed on pedestrian safety and more pedestrian infrastructure is installed.

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A.2 Pedestrian Crossing Evaluation Process Overview The evaluation process may be applied to the concept-level design phase for the following situations: . Road construction and reconstruction . 3R (resurfacing, restoration, rehabilitation) projects . Corridor or intersection restriping . Targeted safety improvements . Road safety audit . Traffic engineering studies . Corridor planning projects . Response to public requests

A.2.1 Evaluation Process Overview The process presented in this guide is intended to assist agencies with evaluating the appropriate location and design elements of pedestrian crossings and increase consistency in the decision- making process. Evaluation of an individual location or multiple locations along a corridor for potential crossing treatments should include the following basic steps, which are further defined below: . Step 1: Review GDOT Complete Streets Policy . Step 2: Collect Data and Make Field Observations . Step 3: Evaluate the Location . Step 4: Select the Pedestrian Crossing Treatment

A.2.2 Documenting the Pedestrian Crossing Evaluation Every pedestrian crossing evaluation should be documented, and relevant material should be prepared in the form of an engineering study for GDOT. The engineering study should include: . GDOT Complete Streets Policy checklist (step 1) . Data collection sheets (step 2) . Crosswalk location evaluation (step 3) . Pedestrian crossing treatment selection (step 4)

A.2.2.1 Step 1: Review GDOT Complete Streets Policy The first step in the evaluation process is to review GDOT’s Complete Streets Policy and determine whether pedestrian infrastructure should be provided at a specified location. The GDOT Complete Streets Policy establishes standards and guidelines for when to incorporate bicycle, pedestrian, and transit accommodations into transportation infrastructure projects. GDOT’s Complete Streets Policy should be reviewed at the beginning of the concept development phase of a transportation project or planning study, on GDOT-owned facilities, to determine whether pedestrian infrastructure should be considered as part of the project. Streets under the jurisdiction of a local agency should also be considered for pedestrian accommodations. Refer to Chapter 9 of the GODT Design Policy Manual to review the Complete Streets Policy. Table A-1 presents a series of questions that break down GDOT’s Complete Streets Policy: Pedestrian Warrants. This table can be used as a tool to check whether pedestrian infrastructure is

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warranted on GDOT-owned roadways. This checklist is intended to help engineers and planners interpret the warrants, the final determination, but should still be made in the context of the warrants. Table A-1. Pre-Evaluation Screening Questions

Questions Y/N Standard Is the project If located in an urban area, is the project a planning study, located in an reconstruction, new construction, capacity-adding, or resurfacing urban area? project which include curb and gutter as part of an urban border area? (Refer to Section 6.7 of the GDOT Design Policy Manual for more information on urban border areas). Is the project If located in a rural, are there existing or planned pedestrian travel located in a generators and destinations along the segment of roadway under rural area? evaluation? (Generators and destinations can include but are not limited to residential neighborhoods, commercial areas, schools, public park, transit stops and stations, and convenient stores). If located in a rural, is there evidence of pedestrian traffic (e.g., a worn path along roadside) at any point along the segments of roadway under evaluation? If located in a rural, have there been pedestrian crashes equal to or exceeding the rate of 10 crashes per ½ mile segment of roadway over the most recent five years for which crash data is available? If located in a rural, has a local or regional adopted planning study identified the need for pedestrian accommodations for any point along the segment of roadway under evaluation? Guidelines Is there a school, college, university, major institution, shopping center, convenience store, park, or another major pedestrian generator along or within close proximity to the segment of roadway under evaluation? Is there a shared use path or transit stop along the segment of roadway under evaluation? Is there an approved development that may generate pedestrian traffic in the future within close proximity to the segment of roadway under evaluation? Is the project in an urbanized area or an area projected to be urbanized by an MPO, regional commission, or local government prior to the design year of the project? Have one or more pedestrian fatalities ever occurred along the segment of roadway under evaluation? Has a vehicle-pedestrian crash occurred in the past five years along the segment of roadway under evaluation? Do any city, county, MPO, or regional commission plans (comprehensive transportation plans, livable community, community development plans, etc.) identify the need for pedestrian accommodations along the segment of roadway under evaluation? Has reasonable community interest related to pedestrian infrastructure been received in the past two to four years?

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A.2.2.2 Step 2: Collect Data and Make Field Observations This section describes the data that may be collected to evaluate crossing locations and select a crossing treatment (steps 3 and 4). Review the following subsections, collect the data described in these subsections, and record the observations/data on the data collection sheets, which are included at the end of this document. These sheets can be printed or used as fillable forms. A.2.2.2.1 Compile Previously Adopted Plans Background information from transportation or community development plans related to the site will help identify previous discussions, assumptions, and decisions made related to pedestrian infrastructure. Proposed and approved site development plans will provide insight into where future pedestrian activity is likely to occur. Together, these documents will help evaluators understand the history, provide direction for future modifications (if any), and support the final recommendation. At the onset of a project, designers should ask the following questions: . Do previously adopted plans and/or concept design documents mention the need for or provide recommendations for pedestrian infrastructure in the study area? . How much pedestrian activity will future developments generate? A.2.2.2.2 Document Existing Infrastructure and Developments Knowledge of the existing roadway configuration, pedestrian accommodations, and adjacent land uses and developments is necessary to determine the type and location of pedestrian infrastructure. When assessing the existing site conditions, consider the following questions found in Table A-2: Table A-2. Existing Site Conditions Assessment

Questions Pedestrian What are the existing pedestrian accommodations (i.e., shared use path, sidewalk, worn Path foot)? Where are the existing pedestrian accommodations (i.e., both sides of the street, one- side)? What is the existing roadway configuration including the width of roadway (from curb to curb), number of lanes, turn lanes, and the presence of painted or raised medians? What is the type (painted, raised, planted, etc.) and dimensions of the median (if applicable)? Are physical barriers present either along the roadway or leading up to the roadway that are channelizing pedestrians to certain crossing points (fences, ditches, vegetation, etc.)? Traffic Are there traffic controls (stop signs, traffic signals, marked crosswalks, rectangular rapid Control flashing beacons [RRFB], pedestrian hybrid beacons [PHB], warning signs, etc.) along the corridor? If there is a traffic signal along the corridor, how long is the pedestrian signal phase? Lighting Are there street lights along the corridor? If so, what is their primary function (i.e., roadway or sidewalk illumination)? Land Uses What are the adjacent land uses or developments (i.e., multi-family housing, grocery store, educational institution, etc.)? Transit Where are the transit (bus or train) stops along the corridor?

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Questions Non- Are there shared use path entrances along the corridor? motorized users Special Are special events (sports games, farmers markets, concerts, etc.) held on adjacent events properties along the corridor? A.2.2.2.3 Observe Pedestrian Activity In order to design useful pedestrian infrastructure, an engineer should have an understanding of the level and type of pedestrian activity along a corridor. This information can be used to identify the infrastructure, traffic operations, and places to install pedestrian crossings. When collecting traffic data, it is important to consider the following questions in Table A-3. Table A-3. Pedestrian Activity Assessment

Questions Pedestrian Where are pedestrians walking and crossing the street? path Are pedestrian crossings at intersections or mid-block? Pedestrian What are the pedestrian volumes during the peak hours of pedestrian use along the volumes segment of roadway, crossing, or corridor under evaluation? When are the peak hours of pedestrian activity (weekends, lunch time, at night, etc.)? Pedestrian What is the pedestrian compliance rate (i.e., are pedestrians crossing at a marked Behavior pedestrian crossing or during a designated pedestrian phase)? Driver What is the driver compliance rate (i.e., are drivers yielding to pedestrians crossing or Behavior waiting the cross the street at a marked crosswalk)? Are drivers frequently exceeding the speed limit?

Peak hours of pedestrian use typically occur during fair weather conditions and could be different than peak hours of vehicular use. The developments and recurring community events in the study area may serve as indicators to determine the best time to collect data. For example, in some scenarios, pedestrian activity may be elevated on weekends or at night, if there are places of worship or restaurants in the study area. Multiple days of data collection may be necessary to observe peak pedestrian volumes. Three days of data collection is recommended but this may be shortened to one day if sufficient data are obtained based on engineering judgment. It is recommended to count pedestrians separately from bicyclists and to take note of the percentage of pedestrians who are under the age of 16, elderly, or disabled. Other questions to consider include the following: . When are the peak hours of pedestrian activity (weekends, lunch time, at night, etc.)? . What is the pedestrian compliance rate (i.e., are pedestrians crossing at a marked pedestrian crossing or during a designated pedestrian phase)? . What is the driver compliance rate (i.e., are drivers yielding to pedestrians crossing or waiting the cross the street at a marked crosswalk)? . Are drivers frequently exceeding the speed limit?

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A.2.2.3 Step 3: Evaluate the Crossing Location This section presents the criteria to consider when recommending a pedestrian crossing be installed along the segment of roadway or corridor and when determining where along the segment of roadway or corridor a pedestrian crossing may be installed. The placement of marked pedestrian crossings at uncontrolled locations depends on several factors, including but not limited to adjacent land uses, pedestrian behavior, current and projected pedestrian volumes, proximity to other marked crossings, presence of a transit stop or shared path, and stopping sight distance. Since every situation is unique, it is not possible to provide a completely standardized process for determining whether a crosswalk may be placed at a given location. Thus, this section is not prescriptive. Instead it describes the criteria to account for when determining where to install a crosswalk. For all scenarios, engineering judgement should be used to evaluate the criteria, situation, and potential for crashes. Review the criteria presented in the subsections and document the evaluation on the location evaluation sheets. A.2.2.3.1 Adjacent Land Uses and Multimodal Transportation Connections Criteria The adjacent land uses are significant factors to consider when determining the need for a pedestrian crossing. Land uses such as commercial shopping centers, convenience stores, schools and parks tend to generate more pedestrian activity than others. The adjacent land uses and the presence of active transit stops (bus or rail), multiuse (shared) paths, or trails can be a used as supplemental data to justify the need for a marked pedestrian crosswalk. If the answer to any of the following criteria in Table A-4 is “yes”, the need for a pedestrian crossing at an uncontrolled location could be justified and the engineer should review the guidance (see Chapter 3) for where to install pedestrian crossing treatments. . Is there a transit stop or multiuse (shared) path/trail along the segment of roadway under consideration? . Are there more than two adjacent land uses (existing or planned) that generate significant pedestrian activity? . Are there special events on a regular basis that generate pedestrian activity? Table A-4. Adjacent Land Use Criteria

Criteria Questions Y/N Is there a transit stop or multiuse (shared) path/trail along the segment of roadway under consideration? Y/N Are there more than two adjacent land uses (existing or planned) that generate significant pedestrian activity, such as commercial shopping centers, convenience stores, schools, and/or parks? Y/N Are there special events on a regular basis that generate pedestrian activity?

A.2.2.3.2 Pedestrian Volume Criteria The number of pedestrians crossing the segment of roadway or corridor under evaluation may be used to support the recommendation for a pedestrian crossing at an uncontrolled location. If new

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developments are planned along the roadway or corridor under evaluation, projected pedestrian volumes may be used as a surrogate for observed pedestrian volumes. The pedestrian volume thresholds are generally as follows: . 20 pedestrians per hour in any one hour, or . 18 pedestrians per hour in any two hours, or . 15 pedestrians per hour in any three hours Youth, elderly, and disabled pedestrians may count as 1.33 times their numerical value towards the pedestrian volume thresholds. The factor accounts for weighting users that potentially have needs that are materially greater than the typical, able-bodied person. . Youth are generally those younger than 16 years old. . Elderly pedestrians are generally those over 65 years old that cannot maintain a minimum 3.5 feet per second walking speed. . Disabled pedestrians are generally those that cannot maintain a minimum 3.5 feet per second walking speed, or who use a wheelchair, walker , cane, or other mobility assistance device. . If a family with an elderly, disabled, or a child under 16 crosses in a group, multiply the whole family by a factor of 1.33. Pedestrian Volume Summary Apply the pedestrian data collected in the field to the thresholds. If the observed pedestrian volumes meet or exceed the thresholds, the need for a marked pedestrian crosswalk may be justified. In this case, the engineer should review the guidance for where to locate the crosswalk and what specific pedestrian crossing treatments to install. Meeting or exceeding the pedestrian volume thresholds does not require the installation of a marked crosswalk nor does it immediately justify the need for specific crossing treatments such as pedestrian hybrid beacons or pedestrian signals; additional data should be applied to guidance in chapter 2 to determine the appropriate treatment. If the observed pedestrian volumes do not meet the thresholds, the need for a marked pedestrian crosswalk cannot automatically be justified. In this case, the engineer may use adjacent land use data to supplement the pedestrian volume data and justify the need for a marked pedestrian crossing. If projected pedestrian volumes are used as a surrogate for observed volumes, follow the recommended actions depending upon whether the projected volume meets or falls short of the thresholds. If projected pedestrian volumes are used to justify the installation of a marked pedestrian crossing, the crossing should be observed one year after the installation of the crossing treatments to verify the pedestrian crossing volumes. Depending on the circumstances, it may take more than a one year for the predicted pedestrian volumes to be realized. Engineering judgement should be applied for the one-year evaluation of the pedestrian crossing facility. A.2.2.3.3 Vehicle and Pedestrian Sight Distance Considerations Pedestrian crossings should shall only be installed at locations with adequate stopping sight distances. AASHTO defines stopping sight distance (SSD) as the distance needed for a driver to see an object in the roadway and bring their vehicle to a safe stop before colliding with the object. The stopping sight distances (SSDs) should be measured and checked against AASHTO minimum SSDs (provided in Tables A-2 and A-3) for locations under consideration. AASHTO defines SSD as the

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distance needed for a driver to see an object in the roadway and bring their vehicle to a safe stop before colliding with the object. In places where drivers must make complex or instantaneous decisions, where information is difficult to perceive, or when unexpected or unusual maneuvers are needed, the minimum SSD may not provide sufficient visibility distances for drivers to respond and perform appropriate maneuvers. In these instances, AASHTO recommends using decision sight distances, as shown in Table A-4. Decision sight distance is the distance needed for a driver to detect an unexpected or otherwise difficult-to-perceive information source or condition in a roadway environment that may be visually cluttered, recognize the condition or its potential threat, select an appropriate speed and path, and initiate and complete complex maneuvers (AASHTO Green Book). Use the design speed, posted speed, or 85th percentile speed of the roadway to look up the minimum SSD and/or the decision sight distance recommended by AASHTO, provided in Tables A-52, A-63, and A-74. It is recommended that the highest value of the design speed, posted speed, or 85th percentile speed is used to determine the minimum SSD. A.2.2.3.4 Vehicle Sight Distance Requirements Pedestrian crossings should be installed at locations with adequate stopping sight distances. The stopping sight distances (SSD) should be measured and checked against AASHTO minimum SSDs (provided in Tables A-2 and A-3) for locations under consideration. AASHTO defines SSD as the distance needed for a driver to see an object in the roadway and bring their vehicle to a safe stop before colliding with the object. In places where drivers must make complex or instantaneous decisions, where information is difficult to perceive, or when unexpected or unusual maneuvers are needed, the minimum SSD may not provide sufficient visibility distances for drivers to respond and perform appropriate maneuvers. In these instances, AASHTO recommends using decision sight distances, as shown in Table A-4. Decision sight distance is the distance needed for a driver to detect an unexpected or otherwise difficult-to-perceive information source or condition in a roadway environment that may be visually cluttered, recognize the condition or its potential threat, select an appropriate speed and path, and initiate and complete complex maneuvers (AASHTO Green Book). Use the design speed, posted speed, or 85th percentile speed of the roadway to look up the minimum SSD or the decision sight distance recommended by AASHTO provided in Tables A-2, A-3, and A-4. It is recommended that the highest value of the design speed, posted speed, or 85th percentile speed is used to determine the minimum SSD.

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Table A-5. Minimum Stopping Sight Distance on Level Roadways

Design Speed (mph) Stopping Sight Distance on Level Roadways (feet) 15 80 20 115 25 155 30 200 35 250 40 305 45 360 50 425 55 495 60 570 65 645 AASHTO, A Policy on Geometric Design of Highways and Streets, 2011

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Table A-6. Minimum Stopping Sight Distance on Grades

Stopping Sight Distance on Grades (feet) Design Speed Downgrades Upgrades (mph) 3% 6% 9% 3% 6% 9% 15 80 82 85 75 74 73 20 116 120 126 109 107 104 25 158 165 173 147 143 140 30 205 215 227 200 184 179 35 257 271 287 237 229 222 40 315 333 354 289 278 269 45 378 400 427 344 331 320 50 446 474 507 405 388 375 55 520 553 593 469 450 433 60 598 638 686 538 515 495 65 682 728 785 612 584 561 AASHTO, A Policy on Geometric Design of Highways and Streets, 2011

Table A-7. Decision Sight Distances

Decision Sight Distance (feet) Design Speed Avoidance Maneuver (mph) A B C D E 30 220 490 450 535 620 35 275 590 525 625 720 40 330 690 600 715 825 45 395 800 675 800 930 50 465 910 750 890 1,030 55 535 1,030 865 980 1,135 60 610 1,150 990 1,125 1,280 65 695 1,275 1,050 1,220 1,365 70 780 1,410 1,105 1,275 1,445 75 875 1,545 1,180 1,365 1,545 80 970 1,685 1,260 1,455 1,650 AASHTO, A Policy on Geometric Design of Highways and Streets, 2011 Avoidance Maneuver A: Stop on rural road – t=3.0s Avoidance Maneuver B: Stop on urban road – t=9.1s Avoidance Maneuver C: Speed/path/direction change on rural road – t varies between 10.2 and 11.2 s Avoidance Maneuver D: Speed/path/direction change on suburban road – t varies between 12.1 and 12.9 s Avoidance Maneuver E: Speed/path/direction change on urban road – t varies between 14.0 and 14.5 s Rev 3.0 A. Draft Specification and Industry Meeting Summary 4/25/19 Page A-10 Pedestrian and Streetscape Guide

Locate the point on the edge of the lane where the pedestrian would step into the vehicle travel lane. Draw a straight line representing the length of the minimum SSD and/or the decision sight distance and measure to a point in the center of the approaching travel lane(s). Lanes should be checked to ensure the “worst case” scenario is accounted for. Check that the area in the SSD and/or decision sight distance triangle is clear of objects that could obstruct the sight distance. Check that the measured stopping sight distance and/or decision sight distance is not obstructed by horizontal or vertical curves in the roadway. If there is on-street parking but currently no vehicles occupying the space, consider if the presence of a parked vehicle would obstruct the sight distance. If there is more than one lane, consider that a vehicle in a through travel lane that has stopped for a pedestrian in the crossing can obstruct the visibility for drivers in other travel lanes. When evaluating the SSD, consider the night-time lighting conditions at the proposed location(s). If illumination at the location is inadequate, then a value of twice the minimum sight distance could be considered to see a pedestrian in the roadway and safely bring the vehicle to a stop in advance of the marked crosswalk. The value of twice the minimum sight distance is most appropriate for a speed of 30 mph or less, based on the typical distance limitation for vehicle headlight illumination. While vehicle sight distance represents sight distance from the driver’s perspective, pedestrian crossing sight distance represents sight distance from pedestrian’s perspective. The pedestrian crossing sight distance is the distance required for a pedestrian to see a vehicle that could potentially conflict with the pedestrian crossing the street (PEDS 2014). Typically, pedestrian crossing sight distance is greater than minimum SSD and decision sight distance. The pedestrian crossing sight distance takes into consideration the pedestrian start up and clearance time, the average pedestrian walking speed, the crossing distance, and the travel speed of vehicles (Minnesota Local Road Research Board 2014). Pedestrian crossing sight distance is defined in Equation 1 where: PedSD = Pedestrian Crossing Sight Distance

S = Design Speed (mph) L = Crossing distance (ft)

Sp= Average pedestrian walking speed (ft/s), default = 3.5 ft/s* (refer to Section A.2.2.3.2 for more information on appropriate walking speeds for older adults and pedestrians with disabilities)

ts= pedestrian start-up and end clearance time (s), default = 3.0 s Equation 1: Pedestrian Crossing Sight Distance 푳 푷풆풅푺푫 = ퟏ. ퟒퟕ푺 ( + 풕풔) 푺풑 Accommodating pedestrian crossing sight distance may be considered for marked crosswalks. Since the crossing distance is a variable in the calculation for pedestrian crossing sight distance, a long pedestrian crossing distance may prove challenging to achieve pedestrian crossing sight distance. On the other hand, treatments that shorten the functional crossing distance (e.g. refuge islands, curb extensions, etc.) can result in lower calculated values of pedestrian crossing sight distance and thereby ease some of the challenges in achieving pedestrian crossing sight distance at a given location.

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Sight Distance Considerations Summary To install a marked crosswalk, the minimum SSD shall be met from both directions of travel at the location. Decision sight distance is appropriate where drivers must make complex or instantaneous decisions, where information is difficult to perceive, or when unexpected or unusual maneuvers are needed. Achieving pedestrian crossing sight distance allows pedestrians entering a crosswalk to see approaching vehicles that are likely to conflict with the pedestrian’s crossing path moving at or below the selected speed. Based on a review of the proposed crossing, determine which criteria is most appropriate for developing the recommended sight distance in the given context. If the actual (measured) sight distance is less than the recommended sight distance, consider removing obstructions to accommodate the recommended sight distance. In addition to removing obstructions, other treatments such as curb extensions, bulb-outs, median refuge areas, traffic control enhancements, or other treatments may help mitigate certain aspects of the vehicle or pedestrian sight distance limitations. If the treatments prove to be impractical, consider relocating the crossing to another location that meets the sight distance requirements that is located as close as possible to the ideal location, and preferably within 300 feet of the location that provides the desired walking route. Other factors being equal, a marked crosswalk location that provides both decision sight distance and pedestrian crossing sight distance is preferred. A.2.2.3.5 Pedestrian Travel Paths and Transit Stop Locations Use the pedestrian behavior data collected to identify a specific location(s) for pedestrian crossing treatments. Consider current pedestrian travel paths and anticipated travel paths; where are people coming from and going to? Is there a logical location for a crossing that would connect the origins and destinations? Consider the appropriate placement of a crossing in relation to transit stops and meet with the transit provider to review pedestrian crossing location options. A.2.2.3.6 Pedestrian Sight Distance Requirements In addition to considering the distance required for a vehicle to stop when the driver notices a pedestrian in the road, it is important to account for the distance required for a pedestrian to see vehicles that could potentially conflict with them crossing the street (PEDS 2014). The latter distance is referred to as the pedestrian crossing sight distance. Typically, the pedestrian crossing sight distance is longer than the vehicle stopping sight distances, and in turn is not satisfied by the minimum stopping sight distance. The pedestrian crossing sight distance takes into consideration the pedestrian start up and clearance time, the average pedestrian walking speed, the crossing distance, and the travel speed of vehicles (Minnesota Local Road Research Board 2014). Pedestrian crossing sight distance is defined in Equation 1 where: PedSD = Pedestrian Crossing Sight Distance

S = Design Speed (mph) L = Crossing distance (ft) Sp= Average pedestrian walking speed (ft/s), default = 3.5 ft/s* (refer to Section A.2.2.3.2 for more information on appropriate walking speeds for older adults and pedestrians with disabilities) ts= pedestrian start-up and end clearance time (s), default = 3.0 s Equation 1: Pedestrian Crossing Sight Distance Rev 3.0 A. Draft Specification and Industry Meeting Summary 4/25/19 Page A-12 Pedestrian and Streetscape Guide

푳 푷풆풅푺푫 = ퟏ. ퟒퟕ푺 ( + 풕풔) 푺풑

A.2.2.3.7 Pedestrian Travel Paths and Transit Stop Locations Use the pedestrian behavior data collected to identify a specific location(s) for pedestrian crossing treatments. Consider current pedestrian travel paths and anticipated travel paths; where are people coming from and going to? Is there a logical location for a crossing that would connect the origins and destinations? Consider the appropriate placement of a crossing in relation to transit stops and meet with the transit agency provider to review pedestrian crossing location options. A.2.2.3.8 Presence of a Median or Two-Way Center Turn Lane Use the physical site data collected to assess whether there is a median located in the vicinity of the logical crossing location. An existing raised median, painted median, two-way left-turn lane, or landscaped area can be retrofitted to provide a pedestrian refuge area by creating a cut-through or providing an ADA-compliant curb ramp. For design guidance on how to convert raised medians, painted medians, and two-way center turn lanes into pedestrian refuge areas, refer to the Pedestrian and Streetscape Guide Chapter 3. When installing or converting to a raised median, consider the impact of vehicular access to driveways and streets, as well as impacts to drainage, parking, etc. A.2.2.3.9 Location of Parcel Access (Driveways) Use the physical site data collected to assess whether there are heavily used vehicular access points (driveways) adjacent to the logical crossing location. Consider whether there is a potential for pedestrian conflicts with right turning or left turning vehicles. Assess the appropriate spacing between the access points and the pedestrian crossing to avoid these conflicts. A.2.2.3.10 Proximity to Other Marked Pedestrian Crossings The appropriate spacing between an uncontrolled pedestrian crossing to the nearest marked crossing is dependent on the site context (i.e., rural, suburban, and urban), the presence of a raised median, pedestrian volume, and traffic flow conditions. Use the physical site data collected to determine the location of the nearest marked pedestrian crossing. Given the site context classification for the segment of roadway under investigation, use the minimum crosswalk spacing guidelines below to determine whether a marked crosswalk can be placed at the desired location. Engineering judgment that includes consideration for site-specific factors should supplement the guidance provided by the table. The guidelines for minimum crosswalk spacing from an existing marked crosswalk or traffic signal installation are provided in Table A-8.

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Table A-8. Minimum Crosswalk Spacing Guidelines

Site Context Street Type Minimum Crosswalk Spacing (feet) Urban Core, Urban, or Local and collector (30 mph or less) with median that 200 Rural Town could be used as a pedestrian refuge island Local and collector (30 mph or less) without median 300 that can be used as a pedestrian refuge island Arterial (intended to serve traffic with posted speed of 300 35-45 mph) Suburban Local and collector (35 mph or less) with median that 300 could be used as a pedestrian refuge island Local and collector (35 mph or less) without median 400 Arterial (intended to serve traffic with posted speed of 400 40-50 mph) Rural Local and collector (40 mph or less) with median that 400 could be used as a pedestrian refuge island Local and collector (40 mph or less) without median 400 Arterial (intended to serve traffic with posted speed of 500 45-55 mph)

Recommended Actions If there is an existing marked pedestrian crossing within the minimum spacing, the installation of another crosswalk is typically not recommended. Instead, it is recommended to take action to direct pedestrians towards the existing marked crossing(s), which will require a field review of actual pedestrian crossing behavior. If the nearest marked pedestrian crossing is farther away than the minimum distance, a marked crossing may be considered for the identified location. If the section of roadway under investigation has the potential for future pedestrian crossing demand, the data collection may be conducted in a manner to provide an opinion as to whether a single crossing would serve a minimum of 75 percent of the total pedestrian activity. If not, then consideration may be given to providing multiple pedestrian crossings. When evaluating the need for multiple crossing locations along a corridor, use the minimum spacing between crossings listed above as a guide, but not a rule. The spacing guidelines (listed above) are minimums, not maximums. Consider the impacts of multiple marked pedestrian crossings on motorist compliance and traffic flow. As noted in Table A-3, the presence of pedestrian refuge island provides the opportunity for closer spacing of marked crosswalks, since the pedestrian refuge island simplifies the crossing task for pedestrians.

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A.2.2.4 Step 4: Select the Pedestrian Crossing Treatment Once the need for a pedestrian crossing treatment is established and the location is identified, the next step is to select the appropriate crossing treatment. The appropriate crossing treatment is determined based on roadway configuration, vehicle volumes and speeds, and presence of a median. This section presents the FHWA baseline recommendations and additional treatments for consideration. To determine the appropriate crossing treatment, use the data collected to identify the basic treatments recommended by FHWA and review the additional design considerations. Design recommendations for the treatments listed in the table can be found in Chapter 3 of the GDOT Pedestrian and Streetscape Guide. A.2.2.4.1 FHWA Pedestrian Crossing Treatment Recommendations Table A-9 is the baseline guide for evaluating treatment types given the vehicle volumes, vehicle speeds, and roadway configuration at the specified location. Use the traffic and roadway data collected to determine FHWA’s baseline recommendations for a crossing treatment (countermeasure). Table A-9: Potential Pedestrian Crossing Treatments and Safety Countermeasures

FHWA, Guide for Improving Pedestrian Safety at Uncontrolled Crossing Locations, 2017.

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A.2.2.4.2 ADA Compliance ADA design standards must be met for pedestrian crossings. See the GDOT Design Policy Manual and PROWAG for further guidance. A.2.2.4.3 Lighting for Pedestrian Crossings Lighting at pedestrian crossing locations significantly increases the visibility of pedestrians during night-time/dark conditions. When installing lighting at a pedestrian crossing location it is important to consider the placement of the lights. Research suggests that the traditional placement of luminance at the crosswalk does not adequately illuminate the pedestrian. FHWA recommends that luminaries be offset from the crosswalk at about 10 feet and provides 20 vertical lux at the crosswalk, as illustrated in Figure A-1. It is recommended that luminance be placed in advance of the crosswalk from the drivers’ perspective. For roadways with traffic traveling in both directions or roadways wider than 44 feet, luminance may be used on both sides of the street (FHWA 2008).

Figure A-1. Crosswalk Lighting Location Recommendation

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A.2.2.4.4 Pedestrian Refuge Islands Providing pedestrian refuge islands at pedestrian crossings reduces the risk of pedestrian-vehicle crashes (Lindley 2008). In addition to the FHWA recommendations provided in Table A-3, pedestrian refuge islands are encouraged on two-way streets with: . A crossing distance of 44 feet or greater, . Vehicle speeds greater than or equal to 35 mph, or . AADT greater than or equal to 9,000 vehicles per day Table A-6 does not provide recommendations for a pedestrian refuge island on roadways with an existing raised median. However, an existing raised or painted median or a two way center turn lane may be retrofitted to accommodate a pedestrian refuge island. For further guidance on installing pedestrian refuge islands, refer to Chapter 3 of the Guide. For locations where a median refuge island cannot be accommodated with the existing roadway configuration, the following guidelines apply: . Consider evaluating a “road diet” or “lane diet’ to create space for a pedestrian refuge islands . Review opportunity for widening the road to provide a pedestrian refuge island, including the possibility of acquiring rights-of-way . Evaluate the potential use of additional pedestrian crossing treatments as listed in Table 3 and described in Chapter 3 of the Pedestrian and Streetscape Guide. A.2.2.4.5 Rectangular Rapid Flash Beacons Rectangular Rapid Flash Beacons (RRFBs), also known as Light Emitting Diode (LED) Rapid-Flash System, Stutter Flash, or LED Beacons, can be installed at mid-block pedestrian crossing locations to increase the driver yielding rate and awareness of potential pedestrian conflicts. In addition, RRFBs can be a lower cost alternative to traffic signals or PHBs. FHWA provides the following guidance on the application of RRFBs: . RRFBs shall be used to supplement a post-mounted W11-2 (Pedestrian), S1-1 (School), or W11-15 (Trial) crossing warning sign with a diagonal downward arrow (W16-7P) plaque, or an overhead mounted W11-2, S1-1, or W11-15 crossing warning sign located at or immediately adjacent to an uncontrolled crosswalk. . For any approach on which RRFBs are used to supplement post-mounted signs, at least two W11-2, S1-1, or W11-15 crossing warning signs (each with an RRFB unit and a W16-7P plaque) shall be installed at the crosswalk, one on the right-hand side of the roadway and one on the left-hand side of the roadway. On a divided highway, the left hand side assembly should be installed on the median, if practical, rather than on the far left-hand side of the highway. . Except for crosswalks across the approach to or egress from a roundabout, an RRFB shall not be used for crosswalks across approaches controlled by STOP signs, traffic control signals, or PHBs.

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A.2.2.4.6 Right-of-Way Availability If there is not enough right-of-way available to provide ADA accommodations or support poles for traffic control devices (if applicable), consider relocating the crosswalk to a location with adequate right-of-way availability. The relocated crosswalk should be as close to the desired crossing location as practical, and preferably no more than 300 feet away. If crosswalk is relocated, sight distance requirements need to be rechecked. If crosswalk relocation is not a feasible option, right-of-way acquisition may be considered to accommodate the pedestrian crosswalk. A.2.3 Evaluating the Safety of Existing Pedestrian Crossings The application of the criteria and recommendations is largely based on the need to improve pedestrian safety. Pedestrian crash data are the mostly commonly used statistic for evaluating pedestrian safety. However, the frequency of pedestrian crashes is generally low enough that using pedestrian crash data as the sole method by which pedestrian crossings are evaluated may not be practical in some cases. Pedestrian compliance and pedestrian-vehicle near-miss data may be used to supplement pedestrian crash data. The following sections provide the Engineer with tools to evaluate surrogate safety data based on pedestrian behavior, which can be used to complement traditional safety data such as pedestrian crash history. These tools are suggested for application in cases where there is an existing pedestrian marked or unmarked crossing that is being formally reviewed for enhanced treatments. A.2.3.1 Measuring Pedestrian Compliance Pedestrian and vehicle compliance, which is a safety‐based performance measure, has proven to be a reliable metric that helps highlight the issues and measures the effectiveness of a solution. Pedestrian compliance measurements may be used to evaluate the safety of pedestrian crossing treatments. The following compliance rates at existing pedestrian crossing locations can be determined based on field-collected data:  Percentage (%) of pedestrians that crossed within the marked crosswalk  Percentage (%) of pedestrians that crossed during the pedestrian phase (WALK signal or active PHB)  Percentage (%) of motorists that stop for pedestrians at the marked crosswalk, as compared to the motorists that did not stop and should have stopped Pedestrian compliance is currently measured via field observations, or field conditions captured on video for manual data processing convenience. Video capture of the field conditions provides a better environment for the person that is performing the manual data processing and provides the opportunity to “review the tape” if there is a question about the data accuracy or reliability. At some time in the future, video processing of pedestrian and vehicle compliance may be available to reduce the level of effort currently required for manual processing. The compliance rates can be evaluated using Table A-10 as a guide. Note that pedestrian compliance will depend on many factors, including traffic volume, street width, traffic signal timing operations, and various pedestrian-specific factors.

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Table A-10: Pedestrian Compliance Rate Evaluation

A.2.3.2 Pedestrian Conflict Detection Potential pedestrian-vehicle conflict, also referred to as “near-miss,” may also be used to supplement pedestrian crash data and evaluate the safety of a pedestrian crossing. The National Safety Council refers to a near miss as an event that did not result in injury, but had the potential to do so. Potential pedestrian-vehicle conflict data can be collected and analyzed with video processing software. Video processing software has the ability to trace the pedestrian and vehicle travel paths and detect potential conflict scenarios. This technology expands the ability to quantify pedestrian behavior and, in turn, provides more data for evaluating the safety of pedestrian crossings. Further Guidance . AASHTO, A Policy on Geometric Design of Highways and Streets (2011) . City and County of Denver, Uncontrolled Pedestrian Crossing Guidelines (2016) . City of Boulder, Pedestrian Crossing Treatment Installation Guidelines (2011) . FDOT, Pedestrian Safety at Mid-block Locations (2006) . FHWA, Informational Report on Lighting Design for Midblock Crosswalks (2008) . FHWA, MUTCD (2009) . FHWA, Safety Effects of Marked Versus Unmarked Crosswalks at Uncontrolled Locations (2005) . FWHA, Guide for Improving Pedestrian Safety at Uncontrolled Crossing Locations (2017) . GDOT, Design Policy Manual, Complete Streets Design Policy, Pedestrian Warrants section 9.4.1 (2017) . GDOT, Intersection Control Evaluation (ICE) Policy (2017) . GDOT, Policy 6780-4: Establishment of Speed Zones . GDOT, Signing and Marking Design Guidelines (2018) . Governor’s Office of Highway Safety, Georgia Strategic Highway Safety Plan, Non-motorized Users (2015) . Lindley, Guidance Memorandum on Consideration and Implementation of Proven Safety Countermeasures (2008) . Minnesota Local Road Research Board, Pedestrian Crossings: Uncontrolled Locations (2014) . MnDOT, Minnesota’s Best Practices for Pedestrian/Bicycle Safety (2013)

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. National Safety Council, Near Miss Reporting Systems (2013) . NCDOT, North Carolina Pedestrian Crossing Guidance (2015) . PEDS, Identifying, Assessing, and Improving Uncontrolled Intersections for Pedestrian Access (2016) . PEDS, Safe Routes to Transit (2014) . TRB, Improving Pedestrian Safety at Unsignalized Crossings (2006)

The outcome of a pedestrian-vehicle conflict evaluation typically includes the number of incidents and/or a heat map showing the density and severity of the near misses, and sometimes short video clips are also provided. These reporting tools may be used to obtain a greater understanding of the conflict points and their relative impact on pedestrian operations, as well as perform before/after studies when targeted safety improvements are implemented.

A.3 Pedestrian Crossings at Uncontrolled Locations Template Engineering Study Contact Information: Project: Prepared by: Study Requested by: Date:

Project Location: GDOT District: Congressional District: County: City:

Street Name: Nearest Intersections: Cross Street Name: Signalized: Yes No Stop Signs: Yes No Cross Street Name: Signalized: Yes No Stop Signs: Yes No

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Reason for Pedestrian Crossing Evaluation:

A.3.1 GDOT Complete Streets Policy Pre-screening Form

Table 1. Pre-Evaluation Screening Questions Question Y/N History Have one or more pedestrian fatalities ever occurred along the segment of roadway under consideration?

Has a vehicle/pedestrian crash occurred in the past five years along the segment of roadway under consideration? Has a reasonable community interest been received in the past two to four years? Land-Use Is the site in an urbanized area or projected to be urbanized by an MPO, regional commission, or local government prior to the design year? Is there a school, major institution, shopping center, convenient store, park, or major pedestrian generator/destination along the segment of roadway or corridor under evaluation? Is there a multi-use path or transit stop on either side of the street along the segment of roadway or corridor under evaluation? Is there an approved development that may generate pedestrian traffic in the future? Physical Attributes Is there a sidewalk or evidence of pedestrian traffic (worn path) present? Is there an existing or has there ever been a marked pedestrian crossing? Projects/Funding Do any local government, MPO, or Regional Commission plans (i.e. transportation, livable community, community development plans, etc.) identify the need for pedestrian accommodations along the segment of roadway or corridor under evaluation? Are there construction or 3R projects planned?

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A.3.2 Data Collection Sheets Map / Site Plan: Some data may be better conveyed visually on a map. In this case, attach a copy of an aerial image, map, or site plan of the segment of roadway or corridor under evaluation and identify/call-out specific data point. Data points should include but are not limited to:  Transit stops  Trials or Share Use Paths  Major Pedestrian Generators and Attractors  New/Planned Developments  Roadway Configuration  Special Events  Pedestrian Travel Paths  Parcel Access or Driveways  Street Lighting  Sight Distance Details  Proposed Location for Marked Crosswalk

Site Context: (Record data below and on a map)

Site Context: Urban Core (Downtown) Urban Industrial/Office Park Suburban (Residential) Suburban (Commercial i.e. Shopping Center) Rural Town Rural

Transit Stops: Yes No Number of Transit Stops: Trail or Shared-use Path: Yes No Number of Entrances (trail heads): Adjacent Land Uses:

Major Pedestrian Generators and Attractors:

Special Events: Yes No Frequency of Occurrence:

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Traffic Data: Time of Peak Pedestrian Use: Day Time Peak Hour Pedestrian Volume: Peak Hour Bicycle Volume: Vehicle Volumes - Annual Average Daily Traffic (AADT) Count: Vehicle Speeds (Posted or 85th Percentile): Pedestrian Compliance Rate (if applicable): Driver Behavior: (Sheets for collecting pedestrian and bicycle volumes and pedestrian compliance are on page 5 and 6) Notes:

Roadway Configuration: Total Number of Lanes: Number of Through Lanes: Number of Turn Lanes: Two-Way Center Turn Lane: Yes No Width of Roadway (Curb to Curb): Median: Yes No If Yes, Median Type: Painted Raised Median Median Width ADA Compliance Median Available (4’x4’ landing): Yes No Physical Barrier (preventing pedestrians from crossings at a certain location): Yes No If yes, what is the physical barrier? Existing Marked Crossings: Existing Traffic Calming Devices: Notes:

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Pedestrian and Bicycle Volumes: In-field Data Collection Sheet Name of Street: Date: Day of Week: Time Interval: User Count Total

Youth, Elderly, and Disabled (YED) Pedestrians

Pedestrians (Non- YED)

Total Count

What are the major travel paths?

Where are people crossing the street?

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How are people crossing the street?

Pedestrian Compliance at Existing Mid-Block Locations (if Applicable): In-field Data Collection Sheet Name of Street: Date: Day of Week: Time Interval: Pedestrians Count Percent of Total

Non-compliant with crosswalk location

Non-compliant with crosswalk signal (if PHB or signal)

Total Count Notes:

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Specific Crossing Locations: (Once a specific crossing location has been identified, complete the follow questions) Street Lights at Crossing Location: Yes No Do they work? Yes No Vertical and Horizontal Luminance at Crossing Location:

Sight Distance Measurement Points:

Is the crossing location within horizontal or vertical curve? Yes No Minimum Stopping Sight Distance from AASHTO: SSD Met? Yes No If pedestrian crossings occur at night at this location, can twice the recommend SSD be met? Yes No If no, what objects are obstructing the sight distance?

Can they be removed? Yes No Nearest Marked Crosswalk: Feet Away To the: N S E W Is the Marked Crosswalk: Signalized Stop Sign Controlled Uncontrolled Do the vehicle access points or driveways create possible right/left turn conflicts? Yes No Previously Adopted Plans Are there previously adopted transportation planning and/or design documents related to the segment of roadway or corridor under evaluation? Yes No

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Names of the plans and agency:

Are there any new commercial or residential developments under construction or planned? Yes No Summarize recommendations (summary can be in bullet notes):

*Attach a copy of the recommendations to the evaluation packet.

A.3.2.1.1 Right-of-Way Availability If there is not enough right-of-way available to provide ADA accommodations or support poles for traffic control devices (if applicable), consider relocating the crosswalk to a location with adequate right-of-way availability. The relocated crosswalk should be as close to the desired crossing location as practical, and preferably no more than 300 feet away. If crosswalk is relocated, SSD requirements need to be rechecked. If crosswalk relocation is not a feasible option, right-of-way acquisition may be considered to accommodate the pedestrian crosswalk. A.3.3 Evaluating the Safety of Existing Pedestrian Crossings The application of the criteria and recommendations is largely based on the need to improve pedestrian safety. Pedestrian crash data are the mostly commonly used statistic for evaluating pedestrian safety. However, the frequency of pedestrian crashes is generally low enough that using pedestrian crash data as the sole method by which pedestrian crossings are evaluated may not be practical in some cases. Pedestrian compliance and pedestrian-vehicle near-miss data may be used to supplement pedestrian crash data. The following sections provide the Engineer with tools to evaluate surrogate safety data based on pedestrian behavior, which can be used to complement traditional safety data such as pedestrian crash history. These tools are suggested for application in cases where there is an existing pedestrian marked or unmarked crossing that is being formally reviewed for enhanced treatments.

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Appendix B. Landscape Maintenance Program

B.1 Example of a Landscape Maintenance Program . Edging: Maintain shapes and configurations of plant beds as installed. . Foreign Matter: Remove extraneous leaves, weeds, trash, limbs and debris from plant beds as necessary to constantly maintain a completely clean appearance. This shall occur at each maintenance visit. . Obtain soil samples from the site for analysis. Follow fertilizing and liming recommendations from testing laboratory. . Weed Control: Use chemical and mechanical means to prevent weeds and/or undesirable grasses from encroaching in mulched areas. Maintain a valid, Georgia pesticide applicator and operator’s license and use chemicals in strict accordance with federal, state and county directives on environmental control. Chemicals must have an EPA approval number. . Watering: The contractor is advised that manual irrigation is to be used as a supplement to rainfall. The contractor is responsible for carefully observing the water requirements for landscaped areas and maintaining healthy, vigorous plant material by manually watering. Water newly planted lawns as necessary to keep the top 2 inches of soil moist. After grass is established, apply water approximately 3 to 4 times weekly during summer (1/4 inch to ½ inch per application). Cut back during the fall, spring, and winter.

B.2 Safety and Chemical Use . All materials and performance of work must meet federal health and safety laws in effect. Chemicals to be used in performance of this contract must carry an EPA approval number. Chemicals must be approved by the City before purchase and implementation. . Contractor must provide and require the wearing of protective clothing, mask, eye protection, etc., during any operation as required or directed by applicable laws, regulations or ordinances, and/or directions of manufacturers of material or equipment. . All equipment must be properly maintained and is subject to inspection by the owner. Remove from premises equipment deemed inoperable or unsafe. Equipment must meet American Standard Safety Specification and OSHA requirements. . The Contractor shall adequately protect workers, adjacent property, and the public, and take necessary precautions for the safety of his employees on the job and of the persons employed at the visited facility.

B.3 Specifics Related to Pruning . Street Trees: Allow the tree to form a canopy type head (for shade), maintain a clear trunk of approximately 7 feet height to allow good visibility. The tree needs no pruning (except for deadwood or growth on the main tree trunk) unless the tree is disorganized and needs pruning in certain areas to achieve balance.

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. Flowering Trees: Allow this plant to form its natural shape. Remove foliage and sucker growth from the stems to approximately 1/3 height of the plant. Allow the tree to achieve a maximum height of approximately 12 feet. Prune stems of the tree each year before spring. . Tree-Form Evergreens: Always remove sucker growth from the stems of these plants to 1/3 the overall height of the plant. Prune the plants approximately two times each summer by removing the new shoots from the top of the plants and causing them to thicken up and spread out. (Do not make globe shapes out of these plants.) . Cherry, Fringe, and Chaste Trees: Remove suckers periodically to promote clear trunk. Prune as necessary to promote healthy growth habits. . Evergreen Shrubs: (Used as a hedge type plant): Allow to form a dense mass of plants. Height to be determined by Landscape Architect. . Low Shrubs: (Used as massed type plants). Do not prune into individual shrubs. Allow to form a dense mass of plants at height no larger than 24 inches. . Medium Shrubs: Prune twice a year minimum. Keep tight in character. Allow to grow such that plants will fill in as background. In medians allow plants to grow no larger than 30 inches, per GDOT/county regulations. . Daylilies and Daffodils: Remove dead blooms/growth once a year to create clean appearance. . Groundcovers: As specified on plant list, allow to fill in and create mass groundcover planting.

B.4 Typical Monthly Landscape Maintenance Guidelines January . Prune trees and shrubs that have become too large or out-of-shape. . Inspect plants, shrubs, and trees and remove any damaged or dead wood. . Inspect planting areas and remove any debris or litter. . Check staking and weather protection of first year plants. . Mulch bed areas as needed to replenish mulch levels. . Transplant any trees and shrubs. . Replace any damaged or dead trees and shrubs. . Check moisture level in planted areas and water if necessary. . Check drainage of planted areas, correct if excessive water persists. . Protect plants susceptible to winter damage where possible during extreme cold periods. . Clean up any litter in bed. . Hand weed beds.

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February . Prune trees and shrubs that have become too large or out-of-shape. . Inspect plants, trees, and shrubs and remove any damaged or dead wood. . Inspect planted areas and remove any debris or litter. . Check staking and weather protection for first year plants. . Mulch bed areas as needed to replenish mulch levels. . Apply pre-emerge herbicides to beds to prevent weeds (Treflan). . Replace any damaged or dead trees or shrubs. . Check moisture level in planted areas and water if necessary (weekly). . Protect plants susceptible to cold damage during excessive cold periods if possible. . Remove any staking on one-year old plantings. . Spot spray any existing weeds with Round-Up. . Reestablish a good edge on bed areas. . Clean up any litter in bed. . Hand weed beds. March . Inspect plants, trees, and shrubs and remove any damaged or dead wood. . Check moisture level in planted areas and water if necessary (weekly). . Start pruning where necessary to maintain shape and form (do not shear). . All Liriope should be cut back to allow new growth to come out and remove winter damage to old growth. . Hand weed bed areas as needed. . Deep-root feed trees (Peter’s 20-20-20). . Clean up any litter in bed. April . Fertilize shrubs, trees, and groundcover area with Nursery Special by Sta-Green or equal. . Cultivate and weed planted areas. . Inspect planted areas and remove any dead plants and replace. . Inspect plant material (shrubs and trees) and prune any dead limbs. . Spot spray any weed problem areas. . Inspect areas for insect and disease damage and treat as necessary. . Prune shrubs after they have bloomed. . Inspect plants and trees for insects and/or diseases and treat as necessary.

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. Clean up any litter in bed. . Hand weed beds. . Aeration, reseeding and fertilization of lawn areas. May . Water/Irrigate planted areas as needed. . Spot spray for weeds in planted areas with Round-Up. . Weed groundcover areas as necessary. . Plant annual color beds for the summer. . Prune shrubs and hedges as necessary to keep shape and form. . Prune any damaged plants. . Clean up any litter in bed. . Hand weed beds. . Reestablish a good edge on bed areas. . Lawn fertilization and weed control. June . Water/Irrigate planted areas as needed. . Spot spray for weeds in planted areas with Round-Up. . Weed groundcover and bed areas as necessary. . Fertilize bed areas. . Hand weed bed areas as needed. . Clean up any litter in bed. . Lawn fertilization and weed control. July . Water/Irrigate planted areas as needed. . Hand weed bed areas as needed. . Spot spray with Round-Up on weeds in planted areas where applicable. . Inspect plant areas for insect and/or disease and treat as necessary. . Prune shrubs and hedges as necessary to keep shape and form. . Prune any damaged plants. . Check bed areas for mulch replacement as needed. . Clean up any litter in bed. August . Water/Irrigate planted areas as needed. Rev 3.0 B. Landscape Maintenance Program 4/25/19 Page B-4 Pedestrian and Streetscape Guide

. Hand weed bed areas as needed. . Spot spray with Round-Up on weeds in planted areas where applicable. . Inspect plant areas for insect and/or disease and treat as necessary. . Prune shrubs and hedges as necessary to keep shape and form. . Fertilize groundcovers and bed areas. . Check bed areas for mulch replacement as needed. . Clean up any litter in bed. . Reestablish a good edge on bed areas. . Lawn fertilization and weed control. September . Water/Irrigate planted areas as necessary. . Hand weed bed areas as needed. . Inspect planted areas for insects and/or disease and treat as necessary. . Prune shrubs and hedges as necessary to keep shape and form. . Prune any damaged plants. . Apply pre-emergent to bed areas (Treflan). . Take soil test if necessary for lime and fertilizer requirements. . Clean up any litter in bed. . Lawn fertilization and weed control. October . Water/Irrigate planted areas as needed. . Inspect planted areas for insects and/or disease and treat as necessary. . Prune any damaged plants. . Remove leaves from planted and lawn areas. . Replace and/or plant any new trees or shrubs. . Clean up any litter in bed . Hand weed beds. . Reestablish a good edge on bed areas. . Aeration, reseeding, and fertilization of lawn areas. November . Check mulch in beds and replace where necessary. . Check planted areas for water requirements. . Hand weed beds.

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. Apply approved anti-desiccant to evergreen trees during the first two weeks . Clean up any leaf letter and trash litter in bed. . Lawn fertilization and weed control. December . Clean up litter and leaves on paved and bed areas. . Check planted areas for water requirements. . Hand weed beds. . Lawn fertilization and weed control.

. FHWA, A Guide for Maintaining Pedestrian Facilities for Enhanced Safety (latest edition) . GDOT, Design Policy Manual (latest edition) . GDOT, Maintenance Office . GDOT, Office of Traffic Operations . GDOT, Policy 6755-9: Policy for Landscaping and Enhancements on GDOT Right of Way (latest edition) . GDOT, Request for Qualified Contractors for Routine Maintenance Services

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Georgia Department of Transportation – Traffic Engineering/Traffic Forecast Projections Studies

The overall contract included four (4) separate task orders, which included sixty-five (65) individual traffic forecasting projects. Grice Consulting Group was responsible for providing professional services for data collection, field inventory and review, traffic forecasts and forecasting studies following the requirements as prescribed in the GDOT Plan Development Process (PDP) and Plan Presentation Guide (PPG). 

Each project scope included the development of existing average annual daily traffic (AADT), existing peak (AM and PM) hourly daily traffic volumes (DHV), base and design year build ADT and DHV and base and design year no-build ADT and DHV. In addition, ADTs and DHVs were developed with 24-hour truck percentages for single unit trucks and combination trucks. All project documentation, including a methodology technical memorandum and traffic forecasting MicroStation drawings were submitted for each project.