Evaluation of Roundabout Safety

While roundabouts are still fairly new in the United States and Wisconsin, their safety benefits have been studied with varied results. In this study, 24 roundabouts built in 2007 or before were analyzed for their safety performance. Three years of before and after crash data were gathered as well as geometric and traffic volume data. An empirical Bayes (EB) analysis was used to examine the safety benefits for total crashes and injury (K, A, B, C) crashes. The EB analysis was performed using the Safety Performance Functions from the Highway Safety Manual. Mixed results were found for total crash frequency but a significant decrease in crash severity was identified. Wisconsin roundabouts had an unbiased estimate of a 9.2 percent decrease in total crashes. National numbers similarly show decreases in total crashes. Wisconsin roundabouts showed a significant 52 percent decrease in injury crashes. Roundabouts nationwide are also experiencing a significant decrease in severe crashes. When evaluating predictors, the speed limit of the approaches did not show a significant impact on the safety of the roundabout. While multi-lane roundabouts seemed to be safer than single lane roundabouts when considering fatal and injury crashes, single lane roundabouts saw the largest decrease in total crashes. Two-way stop controlled intersection conversion to a roundabout had the highest safety benefit compared to all-way stop controlled and signalized intersections.