Research On Variable Speed Limit Control Of Expressway In Bad Weather

In recent years,because of its advantages of high speed,high traffic volume and high service level,the expressway has been developing continuously.However,due to bad weather,the situation of traffic congestion,traffic safety and environmental pollution is very serious.Fog,thundershower,local rainstorm,snow,ice and other adverse weather will seriously affect the highway traffic system which will adverse highway traffic efficiency and driving safety.For example,influencing the driver’s psychology and physiology,reducing visibility and road friction coefficient,damaging the smooth running of vehicles.Now common speed limit methods like lane speed limit and speed limit by vehicle are mainly fixed speed mode,which can not adjust the speed value according to the weather condition and real-time traffic flow.And as a dynamic speed limit method,variable speed limit can judge the traffic flow operation status based on short-term traffic flow prediction,then adjust the corresponding road section,effectively reduce the vehicle speed differences,and ensure the highway driving safety and efficiency.This paper firstly analyzes the theory of variable speed limit of expressway in bad weather.On this basis,a dynamic traffic flow model of expressway with variable speed limit that can reflect the influence of bad weather is established.Then,considering both traffic and environmental conditions,a variable speed limit multi-objective model is proposed.Finally,using VISSIM software to simulate and evaluate the effect of variable speed limit control in bad weather combined with MATLAB program.The main works are as follows:(1)Classifying the common bad weather,then analyzing the influence of bad weather on the expressway traffic system.Taking the Whitemud Drive expressway as an example,the principle and goal of variable speed limit control are explained.(2)Based on the original METANET model,after considering the impact of bad weather visibility,driver non-compliance and variable speed limits influence on traffic flow,the basic dynamic traffic flow model is improved.Then using the Genetic algorithm to calibrate the model.The results show that the improved METANET model can better reflect and predict the operating state of expressway traffic flow under the control of variable speed limit in adverse weather environments.(3)In terms of traffic and environment,after maximizing the total traffic volume of the simulated road section and minimizing the total traffic time of the road section based on the traffic efficiency,minimizing the space-time speed difference of the road section based on safe driving,minimizing the vehicle exhaust emission based on environmental protection,an objective function is established.Based on the maximum vehicle speed and the speed smoothing limit,the constraint conditions are determined,and the genetic algorithm is selected to determine the optimal speed limit value.Among them,for the target of vehicle exhaust emissions,the vehicle acceleration is determined by discreting the speed parameters of the METANET traffic flow model,the vehicle acceleration is used to determine the vehicle specific power,and the vehicle exhaust emissions are calculated through the vehicle specific power calculation.(4)Using VISSIM software and MATLAB program to simulate and analysis.The results show that compared with static speed limit,the variable speed limit control method can effectively reduce the adverse effects of traffic congestion and speed dispersion caused by bad weather,lower the number of traffic conflicts and vehicle exhaust emissions under bad weather.The research results of this article can provide technical means for highway management under bad weather,and it also can be regarded as a reference for improving highway traffic efficiency,traffic safety and environmental benefits under bad weather.