Research On Improved Perimeter Feedback Control Strategy Of Urban Traffic Sub-region

With the rapid development of economy,the number of cars in our country is increasing.The following problems,such as traffic congestion,road safety and air pollution,in turn restrict the speed of economic development.In China with high population density,it is impossible to solve the increasingly serious traffic congestion problem simply by road construction.Therefore,effective traffic control strategies are indispensable to solve the problem of urban traffic congestion.According to the theory of Macroscopic fundamental diagram(MFD),when the traffic flow of the road network reaches the maximum,the cumulative number of vehicles reaches the critical cumulative number.At this time,the road network is saturated and the traffic efficiency of vehicles is the highest.It is found that the control signal will affect the shape of the MFD of the traffic sub-region when the characteristics of the MFD are studied.In this paper,BP neural network is used to model the nonlinear correspondence between the signal timing of the sub-region and the peak of the flow in the MFD,the signal timing of the MFD at the peak of the flow is obtained,and the signal timing of the traffic sub-region is optimized.When modeling the traffic flow in the subarea,the vehicle balance equation with parking element is established by fully considering the parking condition of vehicles in the sub-region.Then,a feedback control strategy is proposed to control the number of vehicles in the sub-region near the critical cumulative number of vehicles for maintaining the highest traffic efficiency in the sub-region.Aiming at the problem of queue overflow outside the perimeter intersection caused by the perimeter feedback control,this paper proposes the concept of extended perimeter and gives the extended perimeter signal control strategy under the perimeter feedback control.According to the green light duration and queue length of the perimeter intersection,the green light duration of the extended perimeter intersection is adjusted to prevent the overflow caused by the queue length exceeding the length of the road section.By using the value of the sub-region travel completion flow and the average vehicle delay as the evaluation index,the VISSIM simulation results show that the perimeter feedback control strategy in this paper can effectively improve the value of the sub-region travel completion flow and reduce the average vehicle delay,and improve the traffic efficiency of the road network.Compared with the perimeter control feedback strategy without the extended perimeter control strategy,the average queue length outside the simulation perimeter using the extended perimeter control strategy is significantly reduced,reducing the risk of queue overflow.Taking the value of the sub-region travel completion flow and the average delay of vehicles as the evaluation indexes,the VISSIM simulation results show that the perimeter feedback control strategy in this paper can effectively improve the value of sub-region travel completion flow and reduce the average delay of vehicles,and improve the traffic efficiency of the road network.