Evidence of Mixed Safety Performance Among Roundabouts Converted from Signalized Intersections

Over the past few decades, roundabouts have become increasingly popular in the Unites States as alternatives to conventional stop-controlled or signalized intersections. Roundabouts reduce the number of conflict points from 32 to 8 as compared to traditional 4-leg intersections and have been shown to reduce crashes and injuries in a number of past studies. However, evaluations of safety performance at roundabout locations with high annual average daily traffic (AADT), are not as conclusive. This study analyzes the safety performance of all roundabouts in Michigan that were known to have been converted from signalized intersections using a before-after empirical Bayes analysis. The study included before and after data for 22 roundabouts and control location data for 56 signalized intersections that were located in the same geographic regions and had comparable AADT. The roundabouts evaluated as a part of this study had generally higher AADT, particularly on the minor road, than roundabouts in previous analyses of this nature. It was found that total crashes significantly increased after conversion, but the results for injury crashes were not conclusive. The results indicate roundabouts may not always improve safety after conversion from a conventional intersection and care should be taken when planning for such conversions, especially at higher volume intersections.