Study On Congestion Mechanismof Urban Expressway Ramp And Junction Intersection

The urban expressway system should have the traffic characteristics of unimpeded,fast and comfortable,but in the main cities of our country,these characteristics are gradually disappearing.The traffic congestion occurs frequently in the connection area of ramp and the adjacent intersection especially during the traffic peak period.Research and analysis on congestion mechanism and traffic coordination,making reasonable management and control methods are significant for improving traffic congestion and operation efficiency of expressway system.Based on a large number of related literature,this paper summarizes the research results of scholars at home and abroad,grasps the latest research trends,and conducts a comprehensive and in-depth study of the coordination control in the connection area of ramp and the adjacent intersection.The main contributions are as follow:1.The characteristics of urban road network in Xuzhou are discussed from four aspects: the development of urban spatial form,road network structure,railway system and current urban expressway system.The urban spatial form of Xuzhou has been established,but its hierarchical function of road network is missing.Although the basic urban expressway system has been completed,its construction is far behind the expansion of the urban area and the development of the economy.The number of main roads and sub-main roads is sufficient,but the proportion is not coordinated.2.The traffic characteristics of the ramp and related intersections are analyzed,and the conclusion is reached that the main factors that influence the service level of weaving section are four factors,such as length of weaving section,width of weaving section,weaving flow ratio and weaving type.Considering the timing of signalized intersection,the evolution process of traffic congestion in the connecting area is divided into four stages in this paper: the stage of congestion formation,the stage of congestion diffusion,the stage of congestion dissipation and the stage of congestion disappearance.And the four processes are analyzed in detail.Based on the traffic wave theory,the congestion mechanism of the ramp and related intersection is thoroughly analyzed.When the traffic density is less than the optimal density,the traffic flow is in a free-running state;when the traffic density tends to or equals the optimal density,the traffic flow appears to follow;when the traffic density is greater than the optimal density,the traffic flow is in a congested state,and traffic congestion occurs.3.Select on-ramp S5 and off-ramp N5 of Cheng Dong Avenue expressway and the intersection of Zhen Xing Road and Cheng Dong Avenue Expressway as a typical simulation test section,and analyzes the traffic congestion problem of Cheng Dong Avenue Expressway and the connection area.Traffic organization and channelization are studied,and a coordinated control system is established which is aimed at the overflow in the connecting area during the traffic peak period.At last,VISSIM is used to vertify the validity of the established model.The research results can provide theoretical asis for alleviating the congestion of urban expressway,and provide engineering design method for the new construction or rebuilding and upgrading projects of urban expressway.