KAI led an international team of experts to develop methods for estimating the safety and operational impacts of U.S. roundabouts and 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 U.S.; evaluated existing international operational and safety analysis models using U.S. Data; created computational procedures to estimate capacity, delay, and queue lengths for approaches to single- and multilane roundabouts using U.S. 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 consideration 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.