The Analysis On Dynamic Features Of Road Traffic Flow In Poor Visibility Based On The Cellular Automata Model

With the rapid development of our country's economy, the national vehicle ownership and the total mileage of highway are growing quickly. The problem of traffic safety is becoming serious day by day while it has brought people immense convenience.According to analyse the traffic accidents in our country, the deaths caused by bad weather are increasing,especially in the dense fog,heavy rain, tunnel and other poor visibility conditions that the accident rate increases by more than 10 times.Therefore,the research of the dynamic characteristics of traffic flow in poor visibility and determining the maximum safety speed are the keys to ensure freeway travel safety. It has important practical significance to set up related criterion for our country.According to study the vehicle driving features under dense fog and tunnel with poor visibility, corresponding model rules are bulit based on Cellular Automata theory .and programme with VB6.0 to simulate the characteristic of traffic flow. The chief contents are as follows:(1)Firstly, the Human - vehicle - road - environmental characteristics in poor visibility on foggy days was analyzed; Secondly, according to these features, on the basis of the NS model and the two-lane CA model, the rules of safety shut-down was amended to establish appropriate rules of operation;Finally, according to the fog regulations of the National Highway , vehicles operation features are researched by changing the maximum limited speed in the condition of different road visibility and the conclusion of the optimal limited speed value was got with the standard of accident rate and traffic volume for safety and efficiency under different visibility.In the same visibility, when the density interval is in [0,0.4],the growth trend of traffic flow is basically linear with the increase of the maximum limited speed,but the growth trend of accident rate is divided into two parts: when the limited speed is higher than a certain degree,the accident rate remarkablely increased.When the visibility interval is in [<50],[50,100],[100,150],[150,200],[200,500](m),the recommended limited speeds are 30,50,70,90, 100km/h.(2) According to the character of changing speed when vehicles go through the tunnel and based on NS model, the corresponding CA model was built .Vehicles get into the system by a form of Poisson distribution using openly boundary contidion. the length of threshold zone in different acceleration probability and the length of transition zone in different deceleration probability are analysed on the condition that the visibility is100m and 150m . It provides foundation to the setting of lighting degree under variable speed limitation in the tunnel.According to analyse statistical data, the conclusions are got as follows:When the visibility of tunnel is 100m and the maximum limited speed is 60km/h,the recommended length of threshold zone is 42~50m,the length of transition zone 136~207m; When the visibility of tunnel is 150m and the maximum limited speed is 80km/h,the recommended length of threshold zone is 84~95m,the length of transition zone 181~287m;...