The Insurance Institute for Highway Safety came out with a report evaluating safety at existing roundabouts in Maryland. They found that most crashes, whether at single lane or double lane roundabouts, occurred on the approaches into the roundabouts not within the circulatory part of the roundabout. In a nutshell, they recommend better landscaping within the middle of the roundabout along with better signing/pavement markings in advance of the roundabout. Both measures are to clue drivers in that there is a roundabout ahead before it is too late for them to slow down.
The report did confirm the safety benefits of roundabouts. Only 25% of the crashes in Maryland at roundabouts between 1993 and 2005 involved injuries. More importantly, there were no fatalities at the 38 roundabouts studied. This isn’t a large sample, but the safety track record is encouraging compared to the safety at intersections controlled with traffic signals. According to the Minnesota Office of Traffic Safety there were 25 fatal crashes at traffic signals in Minnesota in 2006. A very low number, but maybe a few of them would have been avoided with roundabouts.