Variable Speed Limit Control Method For Non-Recurrent Bottleneck Zone

As the aorta of the urban traffic,expressway provides large volume and long-distance transportation services for urban traffic.However,with the increasing demand of Expressway traffic,the non-recurrent bottlenecks caused by unexpected accidents,road construction and other emergencies on expressways are becoming more and more common,which seriously affects the efficiency and service level of expressways,and brings many inconveniences to the normal work and life of pedestrians.At the same time,with the frequent occurrence of unusual traffic congestion,the upstream traffic flow in the bottleneck area has a sudden drop in speed when approaching the bottleneck,which seriously affects the driving safety of the main line traffic flow.Therefore,it is of great practical significance to study this kind of non-recurrent traffic congestion.Variable speed limit control,as an important means of main line control,can effectively alleviate the traffic congestion on the main line of expressway,so it can be applied to the improvement strategy of congestion in non-recurrent bottleneck areas.However,it should also be considered that the variable speed limit control will also have an impact on the surrounding road network when the speed limit is applied to the main line.The main manifestation is that the speed limit will affect the route choice of the main line travelers,thus changing the flow input of the main line of the expressway.In view of the above,this paper establishes a bilevel programming model based on the above analysis to study variable speed limit control and analyze its control effect.The main research work in this paper is as follows:(1)Traffic flow model of non-recurrent bottleneck area.This paper introduces the related concepts and characteristics of Expressway non-recurrent bottlenecks,and defines that the control period is divided into two parts,namely,the period from bottleneck occurrence to bottleneck recovery and the period from bottleneck recovery to normal traffic flow recovery.This paper summarizes the macro traffic flow model of Expressway main line,introduces the cell transmission model(CTM),and improves the cell transmission model accordingly.This paper analyses the traffic efficiency and security in the non-recurrent bottleneck area,and calculates the main line traffic efficiency and security index by using cell transmission model(CTM),which lays the foundation for the model construction.(2)Research on Road Network Equilibrium under Variable Speed Limit Control.Taking the expressway network composed of main road,auxiliary road and peripheral main and secondary road as the research object,this paper summarizes the regulating effect of speed limit on the flow of sections in the expressway network,and discusses the problem of user balanced distribution under speed limit.Finally,combined with non-recurrent bottlenecks and variable speed limit control,the equilibrium of road network from bottlenecks to recovery process is analyzed.(3)Bi-level programming model of road network equilibrium under variable speed limit control.The lower layer is the user equilibrium assignment model under speed restriction,and the upper layer is the optimization model with the minimum total travel time and the minimum change range of traffic flow velocity as the control objective.For the above bilevel programming model,Frank-Wolfe algorithm and genetic algorithm are used to solve it.According to the different control objectives,the control flow charts from bottleneck occurrence to bottleneck recovery and from bottleneck recovery to normal traffic flow are given.(4)Solving the model and doing VISSIM simulation.Firstly,the cell transmission model(CTM)is used to simulate the evolution of traffic flow after the occurrence and recovery of the main line’s non-recurrent bottlenecks.Secondly,the variable speed limit and flow distribution scheme are solved by using MATLAB.At last,the simulation results of VISSIM are compared and analyzed.One is the comparative analysis of cell transmission model and VISSIM simulation results,the other is the comparative analysis of the control effects of variable speed limit and variable speed limit in VISSIM.The results show that the difference between cell transmission model and VISSIM simulation results is small.At the same time,variable speed limit control can effectively improve the traffic efficiency and safety of the main line of expressway.