Research On The Method Of Setting Variable Speed Limits On Highway Under Adverse Conditions

In recent years, the road traffic safety is in a severe situation in our country, although the total number of traffic accidents and death toll has the trend of descending. According to the statistics data from Ministry of Public Security Traffic Management Bureau, speeding is the most serious traffic violations leading to traffic accidents and deaths, therefore, applying suitable speed limit strategies is significant to reduce road traffic accidents and ensure traffic safety.In this article, the model of variable speed limit on highway is studied based on the investigation of current developments of domestic and overseas speed limit management control systems and related models of speed limit. Considering the influences of road alignment, traffic flow, weather situation and other factors on speed and capacity in adverse conditions, the variable speed limit model on highway and its evaluation method are presented, which are as follows:(1) Analyzing the influences of road alignment, traffic flow, weather situation and other factors on speed limit management control in adverse conditions on highway. The influences of various factors on speed are analyzed to determine the maximum safe speed from the point of safety. The influences of various factors on capacity are analyzed to determine the bottleneck area from the point of efficiency.(2) Calculating the maximum safe speed on highway under the influence of multi-factors. Firstly the reference value of the maximum safe speed on highway is determined from the point of driver's psychology and physiology. Secondly the reference value of the maximum safe speed is revised based on the analysis of the multi-factors'influences on speed.(3) Establishing the variable speed limit control strategies on highway by analyzing the influence of adverse conditions on capacity of highway. Taking the potential maximum queue length as the speed limiting control area and aiming at the traffic volume before the bottleneck area which is close to the maximum traffic capacity in the bottleneck area, the coordination control of the traffic flow is carried out to calculate the optimal transitional sequence of the speed limit values in upper section before the bottleneck area which will be dynamically adjusted according to the detected speed distribution and flow information.(4) Evaluating the safety for the speed limiting model by traffic conflict theory and microscopic traffic simulation technology. The traffic safety evaluation process, evaluation index selection and quantitative evaluation method for expressway speed limiting control are presented. At last the evaluation is carried out by an example demonstration to show that the speed limit model has certain practicability.