Research On Variable Speed Limit Method Based On Tunnel Traffic Density Classification

In recent years,the number of tunnel traffic accidents has been increasing in China.In order to find out the causes of tunnel traffic accidents,scholars have made a lot of statistical analysis on tunnel traffic accidents.It is found that rear end collision accounts for the highest proportion of tunnel accidents.The large difference between the driving speed and the specified speed limit value of the tunnel is the main reason for the frequent occurrence of tunnel traffic accidents,which further reflects that the speed limit methods of many domestic tunnels are not suitable for the actual situation of local tunnel traffic.In view of this phenomenon,it is necessary to reasonably specify the tunnel speed limit value,scientifically and reasonably arrange the tunnel speed limit facilities,and formulate a reasonable speed limit mode.Based on the problems existing in the traditional speed limit mode of tunnel,in order to reduce the number of tunnel accidents and improve the traffic efficiency of vehicles,this thesis introduces the hierarchical variable speed limit mode to study the speed limit of tunnel.This research is divided into four parts: tunnel traffic safety impact analysis,variable speed limit method research based on traffic density classification,tunnel variable speed limit technology setting and effect analysis,and Chengdu Chongqing Ring Expressway case study.In the first part of this thesis,the accident characteristics and traffic flow characteristics of the tunnel section of Chengdu Chongqing Expressway are statistically studied,and the relationship between the tunnel traffic flow and the number and severity of traffic accidents is analyzed.In order to study the impact of speed limit on traffic safety,the simulation road section is established in VISSIM software and the basic parameters are calibrated at the same time.Under the effect of speed limit,the changes of various indicators are observed and the effect of speed limit on tunnel traffic safety operation is analyzed.In the second part of this thesis,a hierarchical variable speed limit scheme is proposed to make up for the shortcomings of the traditional fixed speed limit mode.The improved METANET is taken as the basic traffic flow model of the tunnel,and a variable speed limit model is established on the basis of the traffic flow model to specify the speed limit value range of the tunnel and determine the speed limit target.The mixed genetic simulated annealing algorithm is used to solve the objective function value in the variable speed limit model.The third part of this thesis studies the length calculation of tunnel speed limit zone,the setting of tunnel speed limit facilities,and the design of general speed control technology,and then combines the speed limit technology with the speed limit model studied in the previous article.In order to prove that the variable speed limit can guarantee the tunnel traffic safety more effectively than the traditional speed limit,the contrast experiment between the traditional speed limit and the variable speed limit is conducted in the case analysis to observe the effect of the two speed limit modes on the speed limit target under the high-density and low-density traffic conditions of the tunnel.In the last part of this thesis,in order to prove that the hierarchical variable speed limit method studied in this thesis can be applied to tunnels of different lengths,the research object in the case study is extended to the whole tunnel section of Chengdu Chongqing Ring Expressway.According to the traffic congestion level of the tunnel,it can be divided into low-density and high-density tunnels.Under the two tunnel traffic density conditions,a comparative experiment of fixed speed limit and variable speed limit is conducted to observe the change of the target function value of speed limit.In the tunnels of different lengths of Chengdu Chongqing Ring Expressway studied in this thesis,no matter the tunnel traffic is congested or smooth,the graded variable speed limit mode is more effective than the traditional fixed speed limit mode to improve the speed limit target value,thereby improving the tunnel traffic safety and efficiency.From the perspective of traffic safety,the standard difference of vehicle speed in the tunnel is reduced,the dispersion of vehicle speed is reduced,the headway distribution between vehicles meets the safety requirements more,the number of tunnel traffic accidents is effectively reduced,the loss of personnel and property is minimized,and the traffic safety coefficient is improved;From the perspective of traffic efficiency,the adoption of variable speed limit shortens the time for vehicles to pass through the tunnel.During the simulation time,vehicles can travel a longer distance,reduce the time for congestion and queuing,make the tunnel vehicles run more smoothly,and improve the traffic efficiency of vehicles in the tunnel.