nchrp_rpt_672

NCHRP Project 03-65: Applying Roundabouts in the US

KAI led an international team of experts to develop methods for estimating the safety and operational impacts of US roundabouts, and to refine the design criteria used for them. The project was completed in May 2006. The research addressed and developed several topics and tools. The project team updated site inventory and data collection at roundabouts around the US; evaluated existing international operational and safety analysis models using US data; created computational procedures to estimate capacity, delay, and queue lengths for approaches to single- and multilane roundabouts using US data (suitable for inclusion in an update to the Highway Capacity Manual).

In addition, the project team created crash prediction models and methods that relate crashes to traffic and geometric characteristics for all roundabout sizes and types (suitable for inclusion in the Highway Safety Manual); refined geometric and traffic control design criteria; conducted an observational analysis of pedestrian and bicycle behavior at roundabouts; and generated marketing materials to communicate roundabout concepts to elected officials.

KAI then led a team of U.S. and international professionals to produce a second edition of Roundabouts: An Informational Guide as part of NCHRP Project 03-65A. This edition includes a comprehensive update to all chapters, reflecting the new research and advances in best practices that have evolved over the previous decade. This includeed a new roundabout capacity methodology, US specific safety data and safety analysis procedures, updated design guidance, and updated guidance on signing and markings.