Study On Variable Speed Control Method For Expressway Under Ice And Snow Conditions

The expressway is an important component of urban transportation system.It provides a fast and efficient operating environment for the internal traffic of the city by improving the road conditions and the traffic environment so that the traffic flow can be quickly passed through in the form of continuous flow,for what it often plays an important role in the transportation system of a city.However,due to the relatively closed structural design characteristics and its strong attraction to the medium and long distance transportation vehicles in the city,a serious congestion area is often formed on the bottleneck of the expressway if it is not controlled in a timely manner during snowfall,and the congestion area may spread quickly to the upper reaches,eventually leading to a long-distance,large area,long-term obstruction on the expressway.As a relatively new control technology for the expressway,variable speed limit control technology has attracted the attention of a majority of scholars in recent years,and people has made a series of progress in practical applications.However,due to the differences in design conditions and traffic characteristics of the expressways in different regions,coupled with the impact of severe and variable weather conditions on expressway's operations,it often does not get the desired effect when apply a region's speed limit strategy to other regions.So,this article refers to the domestic and foreign scholars' research and application experience in this field and against the characteristics of the urban expressway in the north of China,beginning the study with the impact of ice and snow on expressway traffic.Firstly,we investigate and analyze similarities and differences of the traffic flow on the expressway under normal and ice and snow conditions,mastered the law of the evolution of traffic flow on the expressway under ice and snow conditions;secondly,according to the results of the first step,we build the model of the construction and the key phenomena of the traffic flow on the expressway under ice and snow conditions,and improve the traditional cell transmission model based on the needs;then we propose a variable speed limit control strategy based on Qlearning algorithm,the strategy can be applied to expressway's control under ice and snow conditions,and it is designed to ensure the safety of expressways and improve their traffic capacity;Finally,we take a bottleneck area of an expressway in a certain northern city in China for an example and describe the selection of speed limit sections,the setting of speed limit signs,and the calculation of speed limit values in detail.In addition,we use MATLAB as a platform and apply the improved cell transmission model to build a simulation system for the experimental expressway section.In the simulation system,three methods of no-control,model control,and variable speed control based on Q learning algorithm are simulated.The simulation results show that by using the variable speed limit control strategy proposed in this paper,the congestion time of the expressway is reduced by 93.2% and the efficiency of the expressway during the congestion is improved by 16.7%,what is the best result in the three situations.