Over 3,300 modern roundabouts have been constructed in the U.S. since the 1990s, and most of them have exhibited good to excellent operational and safety performances. However, an issue is slowly but steadily emerging with some multi-lane roundabouts that are experiencing much higher than expected crash rates. The type of crash to be investigated is associated with drivers failing to yield properly at exit – vehicles entering the roundabout from the outside lane collide with vehicles exiting the roundabout from the inside lane. Multiple factors may have contributed to the rise in crashes, such as driver mis-judgement of the available gaps, and lack of positive guidance by lane marking in the circulating lane, etc. Urgent action is needed to determine the root cause of such crashes so that proper solutions can be developed to mitigate the problem before it becomes a widespread issue that may jeopardize the implementation of roundabouts around the country.

Investigate the factors contributing to crashes from Exit-Circulating path conflicts at multi-lane roundabout exits, and develop counter measures to cure this problem.

This study is limited to 2-lane roundabouts, and consists of crash study, site specific design review, speed study, traffic study, traffic conflict study, and developing counter-measures. Identify five or more multi-lane roundabouts that are experiencing Exit-Circulating path conflict crashes, and similar number of multi-lane roundabouts that have comparable traffic demands but are performing well in terms of traffic operation and safety. Study the crash patterns of each roundabout, and the geometric design, signing and pavement marking (on the approach and inside the roundabout), summarize their similarities and differences, and develop hypothesis of the leading causes of the crashes. Perform on-site study to determine if vehicle speeds at critical locations conform to design intent, and use suitable technology to record field traffic data than enables determination of lane-based origin-destination pattern at each multi-lane roundabout intersection and computer assisted semi-automated traffic conflict analysis to determine if the conflict patterns mirror the types of crashes observed at each site. Develop counter-measures in geometric design, signing, and/or pavement marking, etc. that help reduce conflicts, simplify driver task loads, and promote proper yielding at roundabout intersection. Develop training material that helps spread the knowledge. If sufficient funding is pooled together, a PHASE II project may be initiated to implement the proposed countermeasures at select multi-lane roundabout locations that have the exit conflict crashes, and verify the effectiveness of the counter-measures in reducing specific type(s) of traffic conflicts.

Study duration: 3 to 5 years Suggested contribution: $50,000 from each participating state DOT/local agency for the entire duration of the study. All state and local agencies are welcome to participate.