The capacity and traffic safety of one lane and two lane roundabouts in West Germany have been investigated in a research project carried out at the Ruhr-University Bochum. Based on observations of real traffic conditions, a set of provisional formulae for the prediction of roundabout capacity under West German conditions has been developed. These formulae are also used in practice for capacity calculations of roundabouts in West Germany. They have been implemented into the computer program KREISEL which is also able to calculate capacities according to the English (Kimber 1980) and French (Louah 1988) formulae as well as to gap acceptance techniques. On the whole, the capacities of roundabouts in Germany seem to be considerably lower than the values predicted by the English formulae. The range of the German results is between 0.7 and 0.8 of the English values. However, there is a good agreement between French and German results. In accordance with foreign experience, roundabouts in West Germany also provide a considerable increase in traffic safety compared to normal signalised or unsignalised junctions. Above all, accident severity is reduced at roundabouts. However, particular attention must be paid regarding the design of zebra crossings and bicycle paths at roundabouts, since pedestrians and cyclists sometimes do not benefit as much as motorists from the improvements in traffic safety (A).
Abstract