December 21, 2018
The future 8th edition of A Policy on Geometric Design of Highways and Streets (Green Book 8) will reflect the dramatic evolution of the nation’s transportation systems.
In 1984, the American Association of State Highway and Transportation Officials (AASHTO) published the first edition of the Green Book, a compilation of specifications and guidelines for geometric design. Keeping pace with the industry, AASHTO publishes new editions every few years-the most recent being the 7th edition, released in 2018. AASHTO is now working toward the 8th edition.
Over the years, the Green Book has been a primary reference to provide design guidance on highways and streets. Continued shifts toward increasingly multimodal transportation networks, however, make it natural for this industry resource to shift too. Responding to a resolution to integrate further flexibility into design standards, even before the 7th edition was finalized, AASHTO knew the 8th edition had the potential for a comprehensive update. As transportation planners and designers work to meet the full range of road users, they need more than structured dimensional guidance for various land use contexts; they need performance metrics that embrace a comprehensive and flexible design approach to support project decision-making.
Green Book 8 Visioning Process
AASHTO selected Kittelson to lead the Green Book 8 Visioning Project-an effort to conduct outreach and an information review to first establish a “Green Book 8 Vision,” then a “Roadmap” to bring the vision to reality.
This project included evaluating substantive documents/resources for applying performance-based approaches, conducting numerous visioning sessions, and gathering feedback through conferences, webinars, conference calls, and supplemental meetings with practitioners throughout the country. The Green Book 8 Vision developed through this process served as a foundation for continued efforts to advance Green Book 8 development.
The goal of the visioning process was to help move the industry toward a true, performance-based approach in establishing roadway designs that are adaptive to their specific contexts.
Development of Green Book 8
This Green Book 8 Visioning Project resulted in an outline for the 8th Edition that was refined and adopted by the AASHTO Technical Committee on Geometric Design. Using this outline, the NCHRP Project 07-29 Project Team will develop the 8th edition of the Green Book and will integrate performance metrics that meet the full range of users and consider metrics that inform project decision-making comprehensively.
The Four Parts of Green Book 8
The adopted outline consists of four parts. Part I introduces performance-based design concepts and design decision-making. Part II provides performance metrics and an overview of applying a performance-based process framework. Part III covers geometric elements and configurations, using much of the detailed content from Green Book 7.
Part IV is a new set of chapters developed specifically for Green Book 8. These chapters focus on the specific considerations of integrating context classification into roadway planning and design. It will apply principles and guidance from Parts I, II, and III to each context and describe the qualities and characteristics of each context classification. We at Kittelson had the chance to develop this new section of the forthcoming guidebook through NCHRP Project 15-77: Aligning Geometric Design with Roadway Context, and the Draft Part IV Chapters can be accessed as NCHRP Web Only Document 320.
Research Activities Informing Green Book 8
Green Book 8 will be a monumental shift to multimodal, performance-based context sensitive design. As such, it is being informed by a number of outside research activities. Here are just a few:
- NCHRP Research Report 1022: Context Classification Application: A Guide assists transportation planners in identifying the appropriate context classification for an area or a transportation project.
- NCHRP Report 1036: Roadway Cross Section Reallocation: A Guide presents a six-step framework for determining tradeoffs, emphasizing the importance of context and community priorities when deciding which tradeoffs are acceptable and which are not..
- NCHRP Project 17-98, Guide for Intersection Control Evaluation, will assemble best practices and propose processes and tools for consistent evaluation of intersection control alternatives.
We’ve been honored to lead (in the case of Report 1036 and Project 17-98) and serve as a sub (in the case of Report 1022) on these meaningful projects. Each of them contributes a piece to Green Book 8, which will pull together a variety of best practices to provide practitioners with flexible, context-sensitive design guidance.
What’s Next
The NCHRP 07-29 Project Team, led by Texas A&M Transportation Institute (TTI), is currently developing chapters for Green Book 8 with close coordination with the AASHTO Technical Committee on Geometric Design. We look forward to seeing how this monumental document incorporates the Green Book 8 Vision and many other research activities and outcomes that serve as the foundation for this important next edition. Our industry has shifted toward a focused approach for multimodal and context-based design and this Green Book 8 can support practitioners to further develop projects that meet the needs of the wide range of users on our transportation system.