Study On Variable Speed Limit Control In Bottleneck Area Of Highway

In recent years,the expressway network was in a stage of continuous improvement and optimization,but it still could not meet the rapid growth of freeway travel needs.In the bottleneck areas of highways,such as the main line connected with ramp and the area of traffic incidents(accidents,construction sites,etc.),congestion problems were increasingly serious and tended to be normalized,which had greatly increased travel costs and travel time.Variable speed control was considered as one of the effective methods to relieve traffic jams,improve traffic efficiency and improve traffic safety in highway bottlenecks.First of all,this paper analyzed the type and discriminating method of the highway bottleneck area,and analyzed the influence of the traffic flow characteristics in the bottleneck area of highway and the influence of variable speed limit control on the traffic flow in the bottleneck area.Secondly,the Cell Transmission Model(CTM)was selected as the basic traffic flow model for the paper's variable speed limit control.Combined with the traffic flow characteristics of the bottleneck area of the highway and the analysis of the effect of variable speed limit on traffic flow to the CTM,the model was improved to simulate the decline in traffic capacity and the state of traffic flow under variable speed control conditions.The parameter of the model were calibrated and verified.Then,the closed-loop control system was used to describe the relationship between the real-time traffic flow information of the freeway and different variable speed limit control strategies.The value combination of the change range of the speed limit value,the change period of the speed limit value and the speed difference of the adjacent variable speed limit board was used as different variable speed limit control strategies,while the traffic efficiency was used as the target of the variable speed limit system.In order to avoid the one-sidedness of a single index,the paper chose integrated index of the total travel time and the total turnover as the optimized objective function of the variable speed limit system.In order to guarantee the proactiveness of the speed limit strategy,the paper chose the model predictive control(MPC)algorithm to design the speed limit value of the controller in the closed-loop control system.Based on the MPC algorithm,the paper established the relationship between the control target and the control strategy to obtain the optimal variable speed limit strategy.Finally,the model established in this paper was verified by the example of the Xi Han Expressway in China.According to the actual data,the paper calibrated the improved Cell Transmission Model and determined multiple variable speed control strategies.The simulation analysis of different control strategies showed that: using integrated index of the total travel time and the total turnover as the control objective function could improve the reliability of the optimal strategy selection.