Cyclists at roundabouts : the effects of `Continental' design on predicted safety and capacity. Prepared for Department of the Environment, Transport and the Regions DETR, Driver Information Traffic Management Division DITM.

Cyclists are over-represented in accidents at roundabouts in the UK. Large or heavily-trafficked roundabouts are difficult for cyclists to negotiate safely and can be a deterrent to cycling. Recently, roundabouts have become more common on Continental Europe, in countries with high levels of cycle use. The Continental design has a tighter geometry than UK design, typically with radial approach arms, minimal flare on entry and a narrow circulatory carriageway to discourage overtaking. This study modified (on paper) six UK roundabouts, varying from 30m to 90m external diameter, to a "Continental" design. The existing and Continental designs were then compared using the TRL computer traffic model ARCADY/3 (Assessment of Roundabout Capacity and Delay / Version 3). The Continental designs predicted reductions in accidents at the four smaller sites; no overall change at one site and increases at the largest roundabout. Roundabout capacity was reduced and delays were increased on some arms. It is concluded that, at roundabouts with flows below about 2,500 veh/h, and where cycle safety is of concern, modification to a continental design may be a useful option. (A)