Research on Capacity of Roundabouts in Beijing

Weaving section have b1een shown to have an effect on capacity at roundabout approaches, because at weaving sections conflict and interference increases, resulting in a reduction of speed. The weaving section is the bottleneck of the traffic flow. Therefore, it should be given the highest priority in the capacity analysis. The current method of calculating the approach capacity at a roundabout mainly utilizes information about entry and exiting vehicles. Few studies are currently conducted from view of the weaving section in capacity estimation. The purpose of this research is to estimate the capacity of roundabout by modeling weaving gap acceptance at the weaving sections. For this reason, a total of 21 roundabouts which are located at the downtown and the suburb of Beijing are selected to conduct data collection. Significance analysis of speed at weaving sections has been conducted by means of the variance analytic method. Regression models of the entry vehicles and circulating vehicles are built up. Based on gap acceptance theory a new method is proposed to estimate the capacity of roundabouts. Furthermore, the relationship between the left turn and through movements on the capacity of roundabouts is established. The findings from this research demonstrate that capacity estimates with weaving section vehicles result in improved prediction of the actual capacity of a roundabout. Furthermore, the geometrical design of roundabout is another important factor which influence the capacity of roundabout, needs to be further explored.