Theory Model for Traffic Capacity of Unsignalized Roundabout in Urban Road

Many unsignalized roundabouts with multi-entry-lane and multi-circulating-lane are still used in urban road of China, where the situation of traffic flow running is very complicated, and the calculation of traffic capacity of unsigalized roundabout needs further research. The fact that most entry vehicles only cross outside two circulating lanes is found by studying video data collected at the unsignalized roundabout. On the basis of gap-acceptance theory, theory model for traffic capacity of the unsignalized roundabout with multi-entry-lane and multi-circulating-lane under the multi-vehicle-type mixed traffic flow condition is established by assuming that the headway of circulating vehicles obeys M3 distribution and probability analysis. Furthermore, cross-street pedestrians and non-motor vehicles interference and vehicles on the entry lanes giving way to each other are considered to modify the model. The accuracy of this model is verified by a case study. This paper provides a method for calculating the traffic capacity of unsignalized roundabout with multi-entry-lane and multi-circulating-lane.