This article presents the main results of studies carried out in France to ascertain changes in roundabout design, especially in the use of mini roundabouts in Europe. The results will be published in full in a report entitled "General guide for urban crossroads: technical guide on mini roundabouts". The first section presents criteria which enable engineers to determine whether a roundabout is the best option or not. Indicators which suggest that a roundabout may be the best solution include: (a) intersections with more than 4 branches; (b) need to reduce traffic speed along a trunk road; (c) accident rate (accident black spot); (d) considerable fluctuations in daily or seasonal traffic; (e) visual intrusion. Indicators which suggest that roundabouts may not be the correct solution include: (a) steep gradients; (b) large numbers of pedestrians coupled with 2 lane traffic; (c) large numbers of heavy goods vehicles or buses; (d) two wheeled traffic combined with large numbers of lorries; (e) very poor balance of traffic between a main road and a secondary road; (f) the proximity of level crossings or traffic lights; (g) site or layout requiring an oval shape; and (h) the vicinity of shops which would encourage parking on the roundabout. The second section describes the design and layout of roundabouts in France, with brief details of experiments carried out at 4 sites on mini roundabouts, all in urban areas (Grenoble, Valence and Nantes). Before and after studies were carried out to ascertain whether the roundabouts had any effect upon accident rates, speed, traffic flow, and to improve the safety and comfort of pedestrians, cyclists and motorcyclists. Detailed analysis of the results is yet to be carried out, but preliminary findings suggest that traffic flow is improved, speed has decreased, but pedestrians do not like them.
Abstract