Despite the demonstrated safety benefits of roundabouts, some crashes still occur. An Institute study of crashes at 38 roundabouts in Maryland found that four crash types (run-off-road, rear-end, sideswipe, and entering-circulating) accounted for almost all crashes. A common crash type at both single-lane and double-lane roundabouts involved vehicles colliding with the central island. These crashes, which often involved unsafe speeds, accounted for almost half of all single-vehicle run-off-road crashes. Collisions occurred more frequently at entrances to roundabouts rather than within the circulatory roadway or at exits. About three-quarters of the crashes involved property damage. There were no right-angle or head-on collisions, potentially severe crash types that commonly occur at traditional intersections.4
In the study of crashes at Maryland roundabouts, Institute researchers concluded that unsafe speeds were an important driver crash factor. Some drivers may not have seen the roundabout in time. Measures to alert drivers of the need to reduce speeds (e.g., speed limit signs well in advance of roundabouts) and increase the conspicuity of roundabouts (e.g., larger roundabout ahead signs and YIELD signs, enhanced landscaping of center islands, pavement with reflector markings) may help to reduce crashes at roundabouts. Certain design features such as adequate curvature of approach roads also may aid in reducing speeds.