| With the rapid increase of the number of motor vehicles in China,the scale of urban road network is expanding day by day.As the main framework of urban road traffic system,urban expressway bears a lot of traffic demand.With the increasing mileage of urban expressway,congestion and conflict often occur in its own weaving area,which has a negative impact on the traffic operation status of urban expressway and even the upstream section of the main road.Therefore,the study of the relationship between the urban expressway weaving area and the upstream section of the main road has a certain practical significance for improving the operation efficiency of urban expressway and alleviating urban traffic congestion.This paper selects the section of Hangtian bridge on the West Third Ring Expressway in Beijing for field investigation.The section is composed of main road and class a short weaving area.The traffic condition of the section from 06:00 to 20:00 is continuously photographed by video method,and the traffic flow data such as traffic flow,speed and density of the expressway are extracted.On this basis,the influence of urban expressway weaving area on the traffic state of the upstream section of main road is studied.Firstly,based on the survey data,the traffic flow characteristics of urban expressway are analyzed.the internal relationship between the basic parameters of urban expressway traffic flow is studied,and the traffic characteristics of the weaving area and the upstream section of the main road are studied and the traffic flow relationship model is established.The results show that the density and velocity of the road section are linear function.Among them,the upstream traffic volume fluctuates greatly in the early peak stage,then rises steadily to a relatively stable state until the end of the late peak;the density decreases after the early peak,and increases with the increase of the passing vehicles before the late peak;the speed is maintained at a lower level in the early peak stage,and the speed fluctuation increases after the peak period,and the vehicle after the end of the late peak period.The speed is falling.Secondly,the traffic state of urban expressway is divided into free flow,stable flow and saturated flow by using fuzzy c-means clustering algorithm.Factor analysis is used to determine the key influencing factors of the weaving area,that is,the weaving flow and non-weaving flow.Based on the survey data,this paper analyzes the influence of the key influencing factors of the weaving area on the traffic flow of the upstream section of the main road,constructs a mathematical model that can reflect the influence characteristics of the weaving area,and determines the value range of the key influencing parameters of the weaving area under different traffic conditions of the upstream section of the main road.The results show that in the state of free flow and saturated flow,there is only one parameter relationship between interweaved flow and non-interweaved flow,while in the state of stable flow,there are two parameter relationships;and when the interweaved flow ranges of free flow,stable flow and saturated flow overlap,the specific traffic state can be determined according to different parameter relationships.Finally,VISSIM is used for simulation.The simulation results show that the composition of different incoming and outgoing traffic flow in the weaving flow has similar influence on the traffic operation state of the upstream section of the main road,and the different traffic states of the upstream section of the main road can be obtained by changing the weaving flow and nonweaving flow.Through theoretical research and simulation analysis,we reveal the operation characteristics of A-level short weaving section of urban expressway,and determine the influence range of key parameters of weaving section on urban expressway traffic state.The results of this paper provide a theoretical basis for the in-depth study of the impact of urban expressway weaving area on the operation status of the main road upstream traffic flow,and provide theoretical support for the construction of urban expressway weaving area management mechanism and the improvement of expressway traffic operation status. |
