Research On Control Strategy Of Continuous Merging Of Complex Ramp Into Urban Freeway Mainline

Urban expressway is the main artery of road traffic that bears high-capacity traffic demand within the city,and with the increase of car ownership,the congestion problem of urban expressway becomes more and more serious.Entrance ramp control is an important means to alleviate traffic congestion on urban expressways,but the existing entrance ramp control strategies all take the entrance of expressways as the research object,without considering the complex interweaving of multiple ramps inside the entrance.In hilly urban expressways such as Chongqing and Shenzhen,multiple entrance ramps are connected to the mainline of the expressway from a single entrance through large interchanges,and vehicles are intertwined in the interior of the entrance,which makes a large number of traffic flows converge at a single node of the urban expressway,and vehicles merge into the mainline of the expressway at low speed,which reduces the road operation efficiency and causes traffic congestion.The impact of continuous complex ramp convergence on traffic operation is extremely obvious,and in this regard,this paper investigates the problem of continuous convergence of complex ramps into the expressway mainline.First,the paper reviews the existing entrance ramp control methods,analyzes and summarizes the existing single entrance ramp control methods and multiple entrance ramp coordination control methods for urban expressways,and points out the shortcomings of existing studies on the control of complex ramps inside the entrance of expressways.And on this basis,the research direction and research content of the complex ramp continuous convergence control strategy in this paper are determined.Second,to address the research problem of the paper,the characteristics of urban expressways,congestion characteristics of urban expressways and the main control algorithms of urban expressways are described,and the structural characteristics of complex entrance ramps,congestion characteristics and the shortcomings of existing control methods are analyzed to lay the foundation for modeling the traffic flow of complex entrance ramps and expressway mainline.Then,based on the basic principles of the traditional model,a model considering the decreasing capacity and variable cell length after congestion is proposed;based on the operation characteristics of complex ramps of urban expressways,a method is proposed to build a continuous complex ramp traffic flow model of urban expressways based on the consideration of hysteresis.On the basis of the established expressway traffic flow model,a coordinated optimal control strategy is established with the minimum composite index of total travel time and traffic flow density as the control objective and the biogeographic optimization algorithm as the entrance ramp regulation rate solution method.Finally,using the Yanggongqiao Interchange to Shimahe Interchange section of Chongqing Inner Ring Expressway as the simulation object,MATLAB software is applied to establish a metacell topological road network based on the complex ramp continuous merging into the mainline traffic flow model of the expressway,and VISSIM software is used to calibrate the parameters and verify the reliability of the metacell road network.The operating states of the metacell road network under the uncontrolled scenario,ALINEA control strategy,and coordinated optimal control strategy are compared,and the application effects of each control method are analyzed and evaluated in terms of traffic throughput,ramp queue length,and overall delay of the road network.The simulation results show that compared with the no-control scenario,ALINEA can improve the traffic operation efficiency to a certain extent,and the coordinated optimal control strategy can alleviate the traffic congestion well,improve the road traffic volume by 15.3% during the peak period,and reduce the overall delay of the road network by 18%.