Research On Variable Speed Control Method Of Expressway In Fog And Haze Weather

With the continuous development of economy and society,the total mileage of Expressway in China is increasing rapidly.However,the extensive economic model brings about severe negative influence on the environment,which is particularly demonstrated by the haze in autumn.The Chinese people would become quite upset whenever haze is mentioned.As the mode of static speed limit is widely adopted in the expressway of China presently,when visibility is reduced by heavy haze,the administrative departments tend to close the expressway to guarantee peopled security,which,however,causes great inconvenience.To solve this problem,we intend to turn to intelligent transportation system,change static speed limit to dynamic speed limit and use variable speed limit strategy to regulate the dynamic speed limit value,thereby realizing smooth traffic in hazy weather.This thesis firstly analyzes the research status and project application of variable speed limit,based on which it studies the traffic flow data in normal weather and hazy weather by means of actual survey to obtain the influence of different visibilities on traffic flow parameters such as speed,space headway,etc.Then,the cell transmission model which can accurately indicate traffic running state is chosen as the basic model of this thesis and API is introduced to exhibit the influence of hazy weather on the traffic operation.On this basis,the basic model is modified and dynamic traffic flow models when the visibility in hazy weather is less than 200 meters and between 200 meters to 500 meters is respectively established.The variable speed limit control strategy of expressway in haze weather is made based on the modified model,and an optimized one is built with the minimum passage time,maximum traffic capacity and least delay as optimization target and the maximum safety speed,speed difference between adjacent sections and variable speed rangeability as constraint conditions.This model is solved by means of genetic algorithm.At last,the Wanping section of Shanghai-Xi'an expressway(G40)is selected as the simulation section and the software VISSIM and MATLAB is respectively used to realize analog control and online simulation experiment of algorithm to conduct analysis on the simulation experiment data.In order to verify that the method of variable speed limit can effectively improve expressway's passage capacity,reduce traffic duration,solve traffic jams of hazy sections within a short period,smooth the traffic flow and enhance passage efficiency and safety whether the haze is light or heavy.The research results of this paper show that the application of variable speed limit control method in haze weather with visibility less than 200 meters and visibility greater than 200 meters and less than 500 meters can improve the traffic capacity of expressway,reduce traffic time and reduce the probability of traffic congestion.It can provide reference information and basis for the formulation of variable speed limit for bottleneck section of Expressway in haze weather.It has certain practical significance to improve the social benefit of expressway.