A Guide for Achieving Flexibility in Highway Design May 2004 American Association of State Highway and Transportation Officials 444 North Capitol Street, NW Suite 249 Washington, DC 20001 www.transportation.org © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. ISBN: 1-56051-259-8 Publication Code: FHD-1 ©2004 American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. contents Acknowledgments ............................................................................................................ xi Introduction .................................................................................................................... xiii 1. The Project Development Process ............................................................................ 1 1.1 Overview of the Process ................................................................................................ 1 1.1.1 Concept Definition ........................................................................................ 2 1.1.2 Planning and Alternatives Development ........................................................... 2 1.1.3 Preliminary Design ........................................................................................ 4 1.1.4 Final Design and Construction ........................................................................ 5 1.2 Philosophy of Geometric Highway Design ........................................................................ 5 1.3 Design Criteria and Guidelines ...................................................................................... 6 1.3.1 Historical Background ................................................................................... 7 1.3.2 Research Basis ............................................................................................. 8 1.3.3 Intended Use of AASHTO Green Book ............................................................. 8 1.3.4 Background on Design Criteria ....................................................................... 9 1.3.5 Design Exceptions—Introduction .................................................................. 10 1.4 Highway Design Controls .............................................................................................. 12 1.4.1 Functional Classification .............................................................................. 12 1.4.2 Terrain ....................................................................................................... 13 1.4.3 Location .................................................................................................... 13 1.4.4 Traffic Volume ............................................................................................ 13 1.4.5 Level of Service .......................................................................................... 15 1.4.6 Design Driver and Vehicle ............................................................................ 16 1.5 Speed—A Fundamental Input to Design ........................................................................ 17 1.5.1 Selecting a Design Speed ............................................................................ 17 1.5.2 Design in the Lower Speed Environment ........................................................ 19 1.5.3 Design Speed and Traffic Calming ................................................................. 19 1.6 Project Types .............................................................................................................. 20 1.6.1 New Construction ....................................................................................... 20 1.6.2 Reconstruction of Existing Highways .............................................................. 21 1.6.3 Resurfacing, Restoration, and Rehabilitation (3R) Projects ............................... 21 1.7 Design Constraints ...................................................................................................... 22 1.8 Design Decision Making ............................................................................................... 22 1.9 References ................................................................................................................. 23 2. Context-Sensitive Solutions through Community Involvement ............................... 25 2.1 Introduction ................................................................................................................ 25 2.1.1 Identify All Stakeholders .............................................................................. 27 2.1.2 Maintain Timely and Coordinated Stakeholder Input ........................................ 27 2.1.3 Commit to an Open, Creative Approach to Problem Solving .............................. 28 2.2 Establishing Purpose and Need ..................................................................................... 28 2.3 Conducting Project Scoping .......................................................................................... 30 v © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. 2.4 Building an Effective Public Involvement Program ............................................................ 30 2.4.1 Develop a Public Involvement Plan ................................................................ 30 2.4.2 Tailor the Public Involvement Program to Meet Specific Project and Public Needs ...................................................................................... 32 2.4.3 Build Community Consent through Open Communications .............................. 33 2.4.4 Strive for Inclusiveness ................................................................................ 33 2.4.5 Maintain Continuity in the Public Involvement Program .................................... 34 2.4.6 Provide and Communicate Clear, Structured Decision-Making Processes ........... 34 2.4.7 References for Developing an Effective Public Involvement Program .................. 35 2.5 Planning and Conducting Public Meetings ...................................................................... 35 2.5.1 Effective Public Notification .......................................................................... 36 2.5.1.1 Project Web Sites .................................................................. 36 2.5.1.2 Reaching Nonresident Stakeholders ........................................ 37 2.5.2 Public Meeting Content and Format .............................................................. 38 2.5.2.1 Open-House Format .............................................................. 39 2.5.2.2 Formal Meeting Format .......................................................... 40 2.5.2.3 Other Meeting Formats .......................................................... 41 2.5.2.4 Visualization as a Tool for Public Meeting Communications ......... 41 2.5.2.5 Communications at the Meetings ............................................ 42 2.5.2.6 Discussing Real Estate Issues ................................................. 43 2.5.2.7 Follow-Up Activities After Public Meetings ................................. 44 2.6 Role of the Design Professional in the Environmental Process .......................................... 44 2.6.1 Develop Safe, Effective, Creative Alternatives ................................................. 44 2.6.2 Communicate Stakeholder Concerns and Issues to Decision Makers ................ 45 2.6.3 Participate in the Project Decision Process ..................................................... 45 2.6.4 Incorporate Public Input with Environmental Documents .................................. 45 2.6.5 Document Project Decisions ........................................................................ 46 2.6.6 Assure Community Issues Are Addressed through the Construction Phase ......... 46 2.7 Effective Public Involvement is Necessary to Produce Appropriate Outcomes ...................... 47 2.8 References ................................................................................................................ 47 3. Highway Geometric Elements—Design and Safety Considerations For Context-Sensitive Project Solutions................................................................... 49 3.1 Introduction ................................................................................................................ 49 3.2 Horizontal Alignment .................................................................................................... 50 3.2.1 Background on the AASHTO Design Model ..................................................... 51 3.2.2 Risk Assessment Guidelines ......................................................................... 52 3.2.3 Flexibility in the AASHTO Guidelines............................................................... 53 3.2.4 Mitigating Tight Curvature ............................................................................ 54 3.3 Vertical Alignment (Grades) .......................................................................................... 54 3.3.1 Background on AASHTO Green Book Assumptions .......................................... 55 3.3.2 Flexibility in AASHTO Guidelines .................................................................... 55 3.3.3 Mitigating Steep Grades .............................................................................. 55 3.4 Coordination of Horizontal and Vertical Alignment ............................................................ 56 3.5 Sight Distance ............................................................................................................ 56 3.5.1 AASHTO Stopping Sight Distance (SSD) Guidelines ......................................... 56 3.5.1.1 Background on the AASHTO Stopping Sight Distance Model .................................................................... 58 3.5.1.2 Risk Assessment Guidelines .................................................... 58 vi © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. 3.5.1.3 Flexibility in the AASHTO Guidelines ......................................... 60 3.5.1.4 Mitigating Limited Stopping Sight Distance ............................... 60 3.5.2 AASHTO Intersection Sight Distance (ISD) Guidelines .....................................60 3.5.2.1 Background on the AASHTO Intersection Sight Distance Model .................................................................... 60 3.5.2.2 Flexibility in the AASHTO Guidelines ......................................... 61 3.5.2.3 Mitigating Limited Intersection Sight Distance ........................... 61 3.5.3 AASHTO Passing Sight Distance (PSD) Policy ................................................. 61 3.5.3.1 Background on the AASHTO Passing Sight Distance Model ..................................................................... 62 3.5.3.2 Flexibility in the AASHTO Guidelines ......................................... 62 3.5.3.3 Mitigating Limited Passing Sight Distance ................................. 62 3.5.4 AASHTO Decision Sight Distance (DSD) Guidelines ......................................... 62 3.5.4.1 Background on the AASHTO Decision Sight Distance Values .................................................................... 62 3.5.4.2 Flexibility in the AASHTO Guidelines ......................................... 63 3.5.4.3 Mitigating Insufficient Decision Sight Distance .......................... 63 3.6 Cross Section Elements ............................................................................................... 63 3.6.1 Lane Width ................................................................................................ 64 3.6.1.1 Background on the AASHTO Lane Width Guidelines ................... 64 3.6.1.2 Flexibility in the AASHTO Guidelines ......................................... 65 3.6.1.3 Mitigating Narrow Lanes ......................................................... 65 3.6.2 Shoulder Width .......................................................................................... 65 3.6.2.1 Flexibility in the AASHTO Guidelines ......................................... 66 3.6.2.2 Mitigating Narrow Shoulder Widths .......................................... 66 3.6.3 The Roadside ............................................................................................. 67 3.6.3.1 Clear Zone ............................................................................ 68 3.6.3.2 Roadside Elements ................................................................ 70 3.6.3.3 Roadside Design for Existing Facilities ...................................... 72 3.6.3.4 Roadside Design in the Urban Environment ............................... 76 3.6.3.5 Flexibility in the AASHTO Guidelines ......................................... 77 3.6.4 Medians .................................................................................................... 78 3.6.4.1 Medians on Rural Highways .................................................... 78 3.6.4.2 Medians on Urban Highways ................................................... 78 3.6.4.3 Flexibility in the AASHTO Guidelines ......................................... 79 3.6.4.4 Mitigating the Effects of Narrow Medians .................................. 80 3.7 Bridges ...................................................................................................................... 80 3.7.1 Flexibility in the AASHTO Guidelines ............................................................... 81 3.8 Intersections ............................................................................................................... 81 3.8.1 Design Vehicles Control Intersection Features ................................................ 82 3.8.2 Flexibility in the AASHTO Guidelines .............................................................. 83 3.8.3 Mitigating Nontraditional Intersection Design Treatments ................................. 83 3.9 Access Control ............................................................................................................ 83 3.9.1 Flexibility in the AASHTO Guidelines ............................................................. 84 3.10 Pedestrian and Bicycle Facilities .................................................................................. 85 3.10.1 Flexibility in the AASHTO Guidelines ............................................................. 86 3.11 Traffic Calming .......................................................................................................... 87 3.11.1 Overview of Traffic Calming ......................................................................... 87 3.11.2 Leading a Traffic-Calming Study .................................................................. 88 vii © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. 3.11.2.1 Establish Purpose ................................................................ 88 3.11.2.2 Offer Alternatives to Traffic Calming ........................................ 88 3.11.3 Application of Traffic-Calming Techniques ..................................................... 89 3.11.3.1 Consider Route Diversion Effects ........................................... 90 3.11.3.2 Address Overall Public Safety ................................................ 91 3.11.3.3 Implementing Traffic-Calming Plans ....................................... 91 3.12 Developing and Documenting Safety Sensitive Solutions ................................................ 92 3.12.1 Overall Guidance ...................................................................................... 92 3.12.1.1 Avoid Combinations of Geometry Outside Typical Ranges .......................................................... 92 3.12.1.2 Maintain a Reasonable Design Speed .................................... 92 3.12.1.3 Mitigate the Expected Operational Effects ............................ 93 3.12.2 Demonstrating a Commitment to Mitigate Safety Concerns ............................ 93 3.12.3 Documenting Design Exceptions ................................................................. 93 3.13 References ............................................................................................................... 95 4. Legal Liability and Highway Design........................................................................... 97 4.1 Introduction................................................................................................................. 97 4.2 Overview of Tort Liability ................................................................................................ 97 4.3 Basic Principles of Tort Liability ...................................................................................... 99 4.4 Sovereign and Public Employee Immunity ..................................................................... 101 4.5 Discretionary Function Immunity .................................................................................. 101 4.6 Design Immunity ....................................................................................................... 103 4.7 Absence of Decision Making ....................................................................................... 104 4.8 Design Decisions, Negligence, and the Duty of Care ...................................................... 105 4.9 Importance of Fully Evaluating and Documenting Design Decisions .................................. 107 4.9.1 Responsibility for Decision Making ............................................................ 108 4.9.2 Risk Management ................................................................................... 108 4.10 What Context-Sensitive Design Practices will Reduce an Agency’s Exposure to Successful Claims? ........................................................................................... 109 4.11 References ............................................................................................................. 110 Appendix A U.S. Federal Regulations on Environmental Protection Affecting Highway Design ........... 115 Tables 1-1 Evolution of AASHTO (AASHO) Design Policies in the United States ................................ 7 1-2 Guide for Selection of Design Levels of Service ........................................................... 16 1-3 AASHTO Recommended Ranges in Design Speeds ...................................................... 18 2-1 Resource and Other Agencies Typically Involved in Project Scoping ............................... 31 2-2 Public Meeting Formats ............................................................................................ 40 3-1 Controlling Geometric Design Criteria ......................................................................... 50 3-2 Acceptable Shoulder Width Values for Shoulder Functions—Values in Feet (Meters) ....... 67 3-3 Alternative Safety Mitigation Measures ....................................................................... 94 Figures 1-1 Typical Project Development Process ............................................................................. 1 1-2 Public Information Meeting at which Design Alternatives Are Being Shown and Discussed ............................................................................................................. 3 viii © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. 1-3 Alternative Design Hour Volume Curves .......................................................................... 14 1-4 Transit Bus May Be Appropriate Design Vehicle for Urban Intersection Design ..................... 16 2-1 Web Site Page for a Highway Corridor Study .................................................................... 37 2-2 Informal, Open House Public Information Meetings Generate Effective One-on-One Discussions ............................................................................................. 39 2-3 Visualizations Assist Public Understanding of Alternative Design Proposals ......................... 41 2-4 Visualizations Aid Understanding of Design Complexities .................................................. 42 3-1 AASHTO Horizontal Curve Model .................................................................................... 51 3-2 Models for Stopping Sight Distance (SSD) and Parameters for Vertical Curves..................... 57 3-3 Example Stopping Sight Distance Profile ........................................................................ 58 3-4 Major Elements of Rural Highway Cross Sections ............................................................. 63 3-5 Placing Utilities Underground Improves Urban Clear Zones and Corridor Aesthetics ..................................................................................................... 72 3-6 Special Aesthetic Barrier and Guardrail Meeting NCHRP Report 350 Test Requirements ...................................................................................................... 75 3-7 The Urban Roadside Environment Includes Pedestrians, Utility Poles, and Other Objects Close to the Edge of Pavement ......................................................... 76 3-8 Relationship of Access Control to Functional Classification ............................................... 84 3-9 Conversion of Four-Lane Roadway to Two-Lane Roadway with Center Turn Lane and Directional Bike Paths ........................................................................................... 86 3-10 Speed Table in Conjunction with Pedestrian Crossing on Local Street .............................. 90 ix © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. 1 chapter The Project Development Process The construction of a highway or street project is the culmination of a design process that is often lengthy, complex, and involves many agencies and individuals. During each stage of the process, important decisions are made that affect subsequent stages and the overall design outcome. This chapter provides an overview of the entire highway project development process. It includes a discussion of the major stages of a highway project, background on the major inputs to highway design criteria and design, differences in types of projects, and the design decision-making process. 1.1 Overview of the Process The highway project development process can be characterized as having four distinct stages, as illustrated in Figure 1-1. The four stages—concept definition, planning and alternatives devel- opment, preliminary design, and final design—generally apply to all projects from inception through construction and maintenance. Note that, depending on the size and complexity of a project, the overall process can take months to several years. FIGURE 1-1 Typical Project Development Process 1 © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. Departments of Transportation (DOTs) and other transportation agencies utilize a range of termi- nology to describe their process. The process outlined in Figure 1-1 and the terminology employed here are generally accepted. For the purposes of discussion, the process and terminology are as follows: • Concept Definition—The identification of a project, including its need, geographic limits, and other specifics to enable studies to begin. • Planning and Alternatives Development—The broad range of activities that result in the selection of a preferred plan that meets regulatory requirements and is sufficiently detailed to proceed with final design and construction. • Preliminary Design—The initial stage of the final design process to confirm right-of-way needs. • Final Design—Completion of design documents and specifications for construction of the project. 1.1.1 Concept Definition In the concept definition stage, the purpose and need for a project or improvement is identified. Such need may come from regular performance monitoring (e.g., pavement condition, congestion, safety history), from a local governmental request made necessary by actions of others (e.g., in response to land use changes or development), by legislative direction, or by response to an emergency. Concept definition involves defining the need and purpose of an improvement, the lim- its of the project, and often the schedule and funding of the project. A key to context-sensitive planning and design is developing a clear understanding during concept definition of the need for a project, which involves an understanding of the transportation problem and the context of the project area that requires addressing. In short, the concept definition stage represents an important decision of project stakeholders to take action by committing to solving a problem on a specific route or in a specified area or corridor. The details of the solution(s) are arrived at in subsequent project development stages. 1.1.2 Planning and Alternatives Development The planning and alternatives development stages involve that part of the process in which alternatives are proposed and studied, environmental and community impacts are assessed, and decisions are reached about the key physical, environmental, community need, and operational aspects of the proposed project. During this stage, the greatest opportunities and challenges for a flexible transportation solution occur. Once the purpose and need for a project have been determined with public input, design criteria are selected by the transportation agency and reviewed with the project stakeholders. Note that this occurs early in the overall project development process. The basis for the project design criteria will generally be the transportation agency’s design guidelines. Project design criteria should recognize both the functionality of the roadway improvement (its use once it has been improved) and the values of the community. 2 © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law. During the planning and alternatives development stages, designers, working with planners, envi- ronmental specialists, the public, and agencies, have the greatest latitude to propose, study, and evaluate a full range of alternatives. Clearly, it is during this stage of the project that the designer can have the greatest influence on the quality of the design, which includes not only its traffic- carrying capability and safety performance, but also its effects on the community and surrounding land uses. The no-build or no-action alternative is usually considered during this stage. As the designers and community consider various plans, it is always possible that no acceptable solution will be reached that addresses the purpose and need. Each build alternative proposed for the project must satisfy the purpose and need agreed to by the full range of stakeholders. This understanding should be forged in the earliest stages of the project and modified as needed during project development. Appropriate consideration should be given to the environmental, scenic, aesthetic, historic, cultural, and natural resources of the area in addition to serving the motorists and other users in a safe and efficient manner. Accordingly, special attention should be paid to developing and/or refining design alternatives, transportation solutions, or features that are consistent with local interests and values while still addressing the safety and operational needs of the facility. FIGURE 1-2 Public Information Meeting at which Design Alternatives Are Being Shown and Discussed The alternatives development stage normally includes key aspects of geometric design. A feasible alternative is one that meets the project’s purpose and need and is considered constructable and maintainable within the social, economic, and environmental constraints of the project area. This determination normally requires that an alternative be developed to sufficient detail to enable reasonable resolution of construction costs, right-of-way requirements, environmental effects, and traffic operational quality. In most cases, the highway designer prepares a “functional” geometric plan for each alternative to enable such analyses. Thus, geometric design plays a substantive role in this early planning stage. (For more detail on geometric design elements, refer to Chapter 3.) Incorporating public input into the project begins early on during the planning and alternatives development stage (Figure 1-2). Indeed, context-sensitive project teams make an effort to fully understand community values before any concepts or solutions are proposed. This assures that 3 © 2004 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.