Research On The Evolution Characteristics Of Traffic Flow And Congestion Mechanism In Expressway Merging Area

As an important part of urban traffic network,expressway plays a great role in undertaking long-distance travel.In recent years,with the continuous increase of vehicle travel demand,the contradiction between supply and demand has become increasingly prominent.The congestion of the expressway system has become a serious problem faced by major cities.Due to the impact of on-ramp traffic flow,the traffic disorder and the decline of traffic capacity often occur in the expressway merging area,which has become the key node leading to the congestion of the expressway system.Therefore,in order to formulate efficient congestion mitigation strategies,it is of great significance to deeply study the evolution characteristics of traffic flow and the mechanism of congestion formation and propagation in the bottleneck of the merging area.The paper is supported by the content of National Natural Science Foundation of China "Optimum Self-Organization Mechanism and Relevant Design Parameters of Expressway Continuous Interchange Traffic Flow(No.51878236)" and Research Project of Hefei Key Engineering Construction Administration "Research on the Key Technology of Hefei Expressway System Evaluation and Traffic Design(No.2019FFCJ4364)".Firstly,a typical urban expressway merging area was selected as the research object,and continuous vehicle trajectory under various traffic flow states in the merging area were obtained by aerial photography with Unmanned Aerial Vehicle.Image processing technology was used to extract basic traffic flow parameters and vehicle operation characteristic data.Based on the measured data,the profound research has been conducted through descriptive statistics and parameter distribution testing methods at the microscopic and macroscopic levels,including the relationship between the basic parameters of the traffic flow in the merging area,the characteristics of parameters changing with time,the asymmetric behavior characteristics of car-following driving,and the lane-changing characteristics of the on-ramp traffic flow.Then the influence of asymmetric behavior and lane-changing behavior on the capacity of the merging area was analyzed qualitatively and quantitatively.Meanwhile,the reduction coefficient model of capacity under the action of microscopic behaviors was established.According to the research results of the microscopic behaviors and macroscopic characteristics of the merging area,the correlation analysis was carried out,and the general process of congestion formation and propagation was revealed.Finally,the traffic flow evolution characteristics of two consecutive expressways onramps merging area were studied by simulation methods.The driving behavior parameters in the VISSIM simulation system were corrected based on the measured data,and a simulation platform with higher reliability was built.The controlled variable method was used to study the critical distance between interractions of the two on-ramps under different main road and ramp flow combinations.The 500 m distance was used as the research scenario,and the traffic flow evolution characteristics of two consecutive onramps merging area were given.