Study On Traffic Flow State Identification And Congestion Mechanism Of Bottleneck On Urban Expressway

With the increasing contradiction between traffic supply and demand,the problem of urban traffic congestion has become serious in large city areas in China,and the expressway bottlenecks are the major cause of congestion.Taking the traffic bottlenecks congestion on urban expressway as the studied object,this dissertation in depth studied the model and method of state identification and resolving congestion mechanism of urban road traffic flow.It was expected that the findings would provide some hints for traffic management and control in urban expressway system.In order to completely understand the basic characteristics of urban expressway traffic flow,the basic parameters of traffic flow were summarized from macroscopic and microcosmic angles,and the characteristics and applicability of each parameter were analyzed.Then,analysis on the characteristics of urban expressway traffic flow parameters based on traffic flow data curve diagram,it was found that the Van Aerde model could describe the relationship between the traffic flow parameters of urban expressway more accurately and comprehensively.In order to analyze the kinematic wave and traffic capacity of urban expressway traffic bottlenecks,the concept of urban expressway traffic bottleneck was elaborated,and the traffic wave theory was used to analyze the traffic wave propagation process from the point of view of traffic flow parameter relationship.It was found congestion and the capacity of traffic bottlenecks are closely related.By analyzing the influencing factors of urban expressway capacity,the calculation formula of capacity correction coefficient was constructed,and the simulation method of traffic bottleneck regional traffic capacity was put forward.In regards to the identification problems of traffic flow conditions on expressway networks,this paper analyzed the characteristics of urban expressway traffic flow by using the cusp catastrophe theory,and introduced the concept of "chaotic state" and "mutation interval" into the traffic state identification model,constructed based on the cusp catastrophe theory.The model determined the upper and lower thresholds of the velocity and density of the chaotic flow state as the criterion of the free flow state and the congested flow state.Moreover,combining with the simulation data,the criterion of the urban expressway traffic flow statuswas given,so as to achieve the purpose of evaluation and early warning of the actual traffic state.In order to explore the congestion mechanism of the bottleneck on urban expressway,the basic parameters of the Van Aerde traffic flow model were calibrated based on the VISSIM simulation data.Then,the congestion spreading speed velocity,the congestion dissipation speed velocity and the real-time queuing length estimation velocity of the urban expressway traffic bottlenecks were constructed.And based on the example analysis,the effectiveness and reliability of the velocities being used to analyze the characteristics of traffic congestion spreading speed and queuing length were verified.