Research On Urban Expressway Work Zone Variable Speed Limit Control Method

Nowadays,the number of urban expressway reconstruction project is continuously increasing with the speeding up of urbanization process and fastly growing car ownership.The reconstruction project always sets work zone which reducing the vehicle travel space and traffic capacity,coupled with the higher expressway traffic flow,construction personnel,guardrail and machinery,work zone is extremely easy to cause traffic jams and accidents that becomes the expressway bottleneck.The traditional speed limit method is a static speed limit method that can't adapt to the traffic environment,its accuracy is poorer and unreasonable which leads to overspeed vehicles.Variable speed limit is a dynamic speed limit method that through the advanced traffic flow detection technology,ensures the optimal speed limit value to achieve active intervention in the traffic flow and improve the efficiency of traffic and security level.The method of variable speed limit control was adopted to the expressway work zone in the paper which mainly researched in four step:theory,simulation,strategy and optimization.Firstly the basic characteristics of expressway work zone and the variable speed limit control theory were summarized.Then the work zone traffic flow model was established based on cell transmission model.After the variable speed limit control method of work zone was put forward,and through simulation evaluated the effect.Finally the intelligent method was used to optimize the variable speed limit control strategy.The following aspects of the paper specific research contents were include:Firstly,the basic composition,the form and basic features of expressway work zone were summarized,and the traffic parameter characteristics of the work zone were analyzed based on the real traffic flow data.The variable speed limit control theory,the variable speed limit's impacts to traffic safety,traffic efficiency and traffic basic figure were introduced.Secondly,the cell transmission model was selected as the expressway work zone traffic flow model,and combined with the special properties of work zone and the characteristics of variable speed limit control,the cell transmission model was improved considering the capacity decline and variable speed limit.Then,basic method,process,optimization model and constraint condition were put forward.At last,the key parameters of the traffic flow model were calibrated using the real traffic flow data.Thirdly,variable speed limit control system of work zone was built,system composition and functions were introduced.Based on setting up the variable speed limit signs,the single objective variable speed limit control method based on safety and efficiency respectively,and multi-objective variable speed-limit control method based on both safety and efficiency were raised,and the differences and effects among different control methods were compared.Fourthly,the neural network was applied to work zone variable speed limit control,the genetic algorithm to optimize the BP neural network and RBF neural network variable speed controller were designed.The effects of different control method were analyzed and evaluated.