Exploration On Capacity Estimation Of Roundabout Of Beijing

Weaving sections at roundabout have been shown to have an effect on capacity atroundabout approaches, because at weaving sections traffic flow interweave mutuallyand bring out merging points, diverging points, and conflict points, and with theincrease of traffic volume, conflict and interference escalate, resulting in a reductionof speed and increasing delay. The weaving section is the bottleneck of the trafficmovement. Therefore, it should be given the highest priority in the capacity analysis.The current method of calculating the approach capacity at a roundabout mainlyutilizes information about entry and exiting traffic. Few studies are currentlyconducted from view of the weaving section in capacity estimation of roundabout.Based on the existing deficiencies and problems, the dissertation mainly focuseson the weaving section to estimate the capacity of roundabout by modeling weavinggap acceptance. For this reason, a total of21roundabouts that are located at thedowntown and the suburb of Beijing are selected to conduct data collection. By takinggeometric conditions and traffic conditions into account, a new method is proposed toestimate the capacity of roundabouts. The contents include the following aspects:Putting forth some relevant concepts about the capacity of roundabouts. Thisthesis presents the Quasi-saturation condition of roundabout concept and on thisbasis further clarifying the concept of the capacity of roundabouts as the standard todo correlation calculation and build model; The correction factor of the proportion offollowing cars is introduced to evaluate the impacts of the proportion of followingcars on different inner lanes, and the model can be modified with the correction factor.The geometric characteristics and traffic characteristics of roundabouts areanalyzed from two aspects. The paper uses SPSS software to analyze the change ruleof headway with radius on different lanes of roundabouts, the critical headway underquasi-saturation condition can be determined. The regression models of the headwayand the radius on both the outer lanes and the inner lanes are established respectively.Moreover, the relationship between the radius and headway on the capacityof roundabouts is established. Based on the theory of saturation flow rate, themultivariate nonlinear regression of single-lane roundabouts and multi-laneroundabouts are conducted using MATLAB software. And then the real data are takento validate this model. With practical example，the recommended values of the basiccapacity of roundabouts that with different radius and lanes are given.Based on the Quasi-saturation condition of roundabout, the findings from this research demonstrate that capacity estimates with weaving section vehicles result inimproved prediction of the actual capacity of a roundabout, and can better reflect thegeometric characteristics and traffic characteristics. Therefore, this conclusionprovides a theoretical basis and reference point for the city road traffic planning andmanagement and the feasibility study of traffic engineering.