The aim of this paper is to give an overview of safety effects of roundabouts. Emphasis is put on effects for bicyclists. Roundabouts have proven to contribute to traffic safety. On average, reconstruction of an intersection into a roundabout causes a considerable decrease in the number of injury accidents. The effects on accidents with deaths and serious injuries are higher than effects on accidents with slight injuries. The effects on accidents with property damage only are uncertain. Further research is needed to determine more clearly differences of effects depending on the before-types of intersections or the location properties such as the road category or the location within or outside built-up area. The safety effects of roundabouts are considered to be caused by effects on speeds and effects on conflicts. Redesigning of an intersection into a roundabout causes a significant speed reduction in the neighbourhood of the intersection. There exists a correlation between speed and lateral displacement on the roundabout. The effects on conflicts however are not clear. There are indications that roundabouts cause an injury accident reduction also for bicyclists. However, there is a lack in the evidence. At least the observed decrease in accident numbers is smaller for bicyclists' accidents compared to accidents with other road users. No final evidence exists about the differences in safety level between different types of cycle facilities. The available research results indicate that roundabouts with separated cycle lanes are safer than roundabouts with mixed traffic or roundabouts with adjacent cycle lanes. The rate of bicycle accidents (number of bicycle accidents per vehicle kilometre) on roundabouts with separated cycle lanes and priority for bicyclists is somewhat higher compared to separated cycle lanes with no priority for bicyclists. A larger central island appears to be safer for bicyclists. For the covering abstract see ITRD E137489.
Abstract