Speed Limit Control And Simulating Evaluation On Freeway Under Foggy Weather

Foggy weather is one of the main causes of serious traffic accident on expressway, according to statistics, traffic accidents happened in foggy weather accounted for about 9% of the total accidents associated with the weather every year, but accounted for 14% of the deaths. Thus it can be seen that the fog’s influence on traffic safety, so we must study and take measures to reduce the accident severity, improve the driving safety in foggy weather. The thesis put forward a speed zone division and classification method, as the expressway is speed limited, coordinating with on-ramp traffic control, so as to better improve the traffic efficiency and achieve the dual goal of traffic safety in foggy weather. Study is developed from the following aspects:First of all, we hold a traffic investigation on the Beijing-Zhuhai Expressway and Changsha Belt Expressway, investigation period is divided into foggy weather and normal weather conditions, obtain the following data:traffic volume, traffic composition, the speed and the headway in different visibility conditions, use statistical analysis to get the influence of visibility on the speed and distance distribution.Secondly, in view of the defects of various methods, the thesis proposes a speed zone division and classification method, which is more specific. The thesis will introduce the specific characteristics of the speed limit method, the partition basis, the determination of the characteristics of each partition and segment length, grading basis and method, and then, based on AASHTO and NCHRP parking stadia model compute safe speed under different conditions, revise and determine the limit speed in different visibility in core of speed zone.Then, considering that there is a close relationship between speed and flow rate, the speed limit management need to reduce the traffic efficiency as little as possible at the same time, the traffic flow- speed coordinated control model is put forward. According to the limit speed and the safety distance of the expressway’s main line to determine its capacity, then on the basis of the surplus capacity to compute ramp rate, control the traffic capacity of the expressway’s main line, to keep the safest and the best traffic operation state.Finally, in order to verify the validity of the speed zone division and classification speed limit method, and the scientificity of the traffic flow- speed coordinated control model, using VIS SIM to simulate and evaluate. With the investigate data to calibrate the related parameters, and on this basis, simulate the no speed limit, partitioned speed limit 80Km/h, non-partitioned speed limit 80Km/h, partitioned speed limit 60Km/h, and non-partitioned speed limit 60Km/h traffic condition. Select the average speed, travel time, lane changing times and front spacing as evaluation index, the simulation results show that:partition can be more effective in reducing the speed of speed, and let the traffic flows more stable.