Research On Variable Speed Control Of Urban Expressway

The rapid development of urban expressway in China has become an important part of urban traffic network.However,traffic accidents such as rollover,scratches,collision often occur at its entrance ramps,exit ramps and congestion sections,which are mainly caused by high-speed vehicles.These traffic accidents not only bring losses to the lives and property of the people,but also lead to road congestion,the low utilization of road resources and high vehicle emissions.Variable speed limit control(VSL)is an expressway control system used to prevent traffic accidents and improve road capacity.In order to reduce traffic accidents and vehicle travel time due to high-density traffic flow and make the most of road capacity,the main purpose of variable speed control is to achieve the best traffic flow and density under the condition of traffic safety.First,taking the bottleneck sections of expressway as the research objects,this paper analyzes their traffic flow characteristics,and proposes the control strategy,process and application range of variable speed limit.Second,considering drivers' safety,based on analysis of CTM model,this paper analyzes the influence of the rain and snow weather on variable speed limit,and put forward the methods for determining the safety speed limits with respect to the road alignment and the vehicle stability respectively.Finally,a variable speed control optimization model of the bottleneck area of urban expressway is formulated with the macro traffic flow model.Its algorithm is designed for finding the optimal speed limit value through several iterations.Its effect is analyzed through VISSIM simulation,and then its efficiency is verified.