A microscopic computer simulation model of roundabout entry operation, which can simulate the phenomena that vehicles leaving by the previous exit disturb entry vehicles, is built to study the influences of leaving vehicles on entry capacity and the determination of entry capacity formula in Switzerland. The comparisons between simulation results and field observations indicated that the simulation model can reproduce the real situations adequately in terms of maximum entry flow. The model is applied to study the influences of leaving vehicles on entry capacity and to determine the entry capacity formula. The results show that the larger the travel distance between the conflict point of exit and conflict point of entry, the fewer the disturbance of leaving vehicles on entry vehicles. If the distance is large enough, then the disturbance will disappear. The entry capacity formula obtained from the simulation study can take account of the influence. Field observations made in Switzerland have confirmed this formula gives better predictions than the formulae proposed by Kimber, CETUR and Harders. This new entry capacity formula has been adopted in the new Swiss Guide On Roundabout Design.
Abstract