Urban Expressway Off-ramp And The Surrounding Road Network Coordinated Optimization Based On Bi-level Programming

Expressway system as the aorta of urban road network,is an important support and a main guarantee for the city traffic fast and efficient operation,its larger design capacity carries the main major transportation of each urban area.The on-ramp and off-ramp as links between the internal traffic flow and the external traffic flow of the expressway system,are the important nodes that the expressway main road and the urban ground traffic correlation cross.The connection is the area where the continuous flow and intermittent flow are interchanged and interact with each other,and it is easy to form a traffic "bottleneck",especially in the peak period,when the traffic congestion is serious,the ramp vehicle queuing even back to the expressway main road,and then affecting the whole smooth and system operating efficiency.Therefore,the coordinated optimization of urban expressway system and the surrounding road network,the city traffic resources sharing,complementary and successive development has a significant function.The main works of this paper are as follows:(1)Related researches on the domestic and foreign expressway and the surrounding road network system are summarized and combed.Additionally,the bi-level programming theory,user equilibrium assignment model,particle swarm algorithm,Frank-Wolfe algorithm and related traffic delay calculation method and so on are introduced.(2)This paper compares the traffic characteristics difference of the grade roads in the urban expressway corridor,analyzes the reasons of the traffic “bottlenecks” of the connection area,and demonstrates the necessity of integration managing the whole system road resources from the space.(3)Bi-level programming model with the idea of "balancing the road resources and dividing the traffic pressure" are constructed.The upper model is a dynamic traffic split-flow model.The traffic demand is taken as the control variable,the road capacity is the constraint condition and the objective function is determined by the minimum total system delay to determine the optimal splitting ratio of auxiliary road.The lower-level planning model is a standard traffic flow assignment model to determine the shortest path of the shunt vehicle and the distribution of traffic flow in each section.In the model,the parameters such as the bypassing delay of the auxiliary circuit,the waiting delay of the vehicles importing other lanes and the interleaving delay are taken into account in the model.Then building an example road network,the optimal proportion of the system under different traffic demand are solved,and the total delay ratio of the system is analyzed in the three cases such as no shunt,fixed shunt,shunted by model.(4)Yanshan Interchange and the surrounding road network in Jinan are taken as examples,and the Vissim simulation software is used to coordinate optimize and simulate the region.By comparing the before and after optimization delay of the expressway off-ramp and the total delay,the results show that the "bottleneck" congestion is improved greatly and the efficiency of the system is greatly improved,Which verifies the feasibility of proposed model in the process of actual road network optimization again.