Converting intersections to roundabouts: effects on accidents with bicyclists

Abstract

A before-and-after study of injury accidents with bicyclists on 95 roundabouts in Flanders-Belgium was carried out. The study design accounted for effects of general safety trends and regression-to-the-mean. Conversions of intersections into roundabouts turn out to have caused a significant increase of 29% in the number of injury accidents with bicyclists on or nearby the roundabouts. The increase is even higher for accidents involving fatal or serious injuries (50%). Compared to the formerly proven favourable effects of roundabouts on safety in general, this result is unexpectedly poor. However, the effects of roundabouts on bicycle accidents differ depending on when these roundabouts are built inside or outside built-up areas. Inside built-up areas the construction of a roundabout did increase the number of injury accidents involving bicyclists by 48%. For accidents inside built-up areas with fatal or serious injuries, we see an average increase of around 80%. However, outside built-up areas the zero-hypothesis of ‘no safety effect for bicyclists’ cannot be rejected, but also there the best estimate is an increase of accidents by 5% although not significant.