Challenge
The original Federal Highway Administration (FHWA) Roundabouts: An Informational Guide, published in 2000, was a landmark document in the United States on roundabout planning, analysis and design practices. Following its publication, roundabout experience in the United States grew exponentially, with new and improved practices emerging around the country that, increasingly, were not reflected in the guide. In addition, a major national research study on roundabout operational, safety and design performance (NCHRP Report 572, led by Kittelson) needed to be incorporated. A second edition of the guide was needed to integrate the research and latest design practices.
Solution
Kittelson led the project team that produced the second edition, a document that would be published as NCHRP Report 672. We conducted a series of focus groups with practitioners to learn what worked well with the first edition and what needed updating. Kittelson also led the delicate effort to forge consensus across a wide spectrum of analysis and design philosophies and practices. A performance-based design process, building on the framework of the first edition, forms the foundation of the second edition, with emphasis on principle-based practices and balancing trade-offs that emerge with individual projects.
The Outcome
Presenting the State of the Art in National Roundabout Practices
NCHRP Report 672 includes a comprehensive update to all chapters, reflecting new research and advances in best practices that have evolved over the previous decade. The report outlines a new roundabout capacity methodology and U.S.-specific safety data and analysis procedures, and provides updated guidance on design and on signing and markings. FHWA adopted NCHRP Report 672 as the official update to the first edition, and the American Association of State Highway and Transportation Officials (AASHTO) and individual states have adopted it into their design standards and practices. NCHRP Report 672 is often held as a model for a performance-based design practices.
