Research On Variable Speed Limit Control Strategy Of Expressway Traffic Flow

In the context of new urbanization,the increase in the size of the urban population has placed higher demands on the supply of urban transportation.As a high-speed connection bridge between urban areas,urban expressways play an increasingly important role in the urban transportation network.However,due to the rapid growth of urban car traffic,as well as the fast road itself has a large traffic volume,fast speed,short distance between the road,etc.,urban expressways is faced with frequent traffic accidents and traffic congestion.The inherent static speed limit control can effectively control the vehicle speed and increase road safety during the urban traffic peak time,but the control effect is not ideal for the sudden increase in traffic and congestion during the rush hour.The variable speed limit control can make short-term predictions of the road according to the real-time traffic flow conditions,and optimize the speed limit control to relieve the congestion pressure of the traffic flow on the bottleneck area during the rush hour.It is an important part of precise and scientific urban traffic management system.This paper takes the expressway traffic flow at rush hour as the research objective.Based on the improvement of the cell transmission model,a predictive control algorithm is used to establish a variable speed limit control strategy selection model.First,the realization of the basic traffic flow simulation function and speed limit control function of the CTM model was completed through python programming,and the simulation model was constructed by taking the Chengdu Riyue Avenue Expressway as an example.Then the predictive control algorithm is used in the simulation model to realize the variable speed limit control of the system,and12 different variable speed limit control strategies are formed by using different control periods and speed limit value change ranges,and simulation experiments are carried out respectively.Finally,the total system delay time(TTD),total vehicle turnover(TTF)and the total ideal speed difference(TVD)between the bottleneck area and the upstream area are used as evaluation indicators to evaluate the simulation results of different speed limit control strategies.The results show that the variable speed limit control has a significant optimization effect on reducing the total delay time(TTD)and the total ideal speed difference(TVD)of the system in congestion,but the optimization effect on the total vehicle turnover(TTF)is not ideal.Among them,control strategies 5 and 6 have the best effect on system improvement,reducing the total delay time of the system by more than 35%,reducing the total ideal speed difference by 55%,and effectively reducing the adverse impact of the traffic jam on the expressway system at peak times.