Accidents at 4-arm roundabouts

The report gives the findings of a study of personal injury accidents at a sample of 84 four-arm roundabouts on main roads in the UK. The study includes small roundabouts and roundabouts of conventional design, in both 30-40 and 50-70 mile/h speed limit zones. Tabulations are given showing accident frequencies, severities, and rates by roundabout type. The accidents are further analysed by type (entering-circulating, approaching, single-vehicle, etc) and by road-user involvement (cyclist, motorcyclist, pedestrian, etc). The accident frequencies by type are related to traffic flow and roundabout geometry using regression methods. Equations are developed to enable roundabout accidents to be predicted to use in design and appraisal. The report illustrates the features of the prediction model, and includes a discussion of prediction errors. (A)