The objective of the research project described in this paper was to develop a formula for calculating the capacity of roundabouts. These formulae were developed by use of an empirical procedure and regression techniques. Therefore, traffic flow at several roundabouts was observed and recorded by video equipment. Based on the assumption that the entry flow was saturated, traffic flows of entering and circulating vehicles were analyzed and counted in 1-minute intervals. Based on these data samples, a provisorial formula has been developed for the prediction of roundabout capacity. Four different curves have been specified according to dependence upon the number of lanes in the circular and the entry. These curves are used in practice for capacity calculations of roundabouts in Germany. Furthermore, an investigation of accident data is described in this paper. In particular the accident research confirmed considerable increase in traffic safety at roundabouts compared to signalised or unsignalised intersections. Accident severity is reduced at roundabouts. It was found that the roundabout is a good solution to increase traffic safety.
Abstract