Study On Speed Limit Of Freeway In Foggy Day Based On Traffic Flow Condition And85%th Speed

With the rapid development and construction, peoples’ travel is more convenient and efficient than before. At the same time, the accidents caused by disastrous weather like snow, fog and rain is keeping increasing. And the severity of accidents on freeway is much greater than that on highway. According to annual statistical reports of Road Traffic Accident, the accidents caused by rain, snow and fog account for39%of total accidents on freeway. And fog is the second only to rain as an important disastrous factor among all the disastrous weather. The paper mainly studies the traffic flow characteristics and the method of calculating speed limit value under low visibility condition in foggy day.First, the paper analyses the characteristics of traffic flow on freeway under low visibility condition in foggy day. Through classifying vehicles and lanes into different types, the paper analyses the changes of speed, density, volume, and concludes some general characteristics of traffic flow.Second, based on the influence of volume and visibility on the speed, the paper fits an average speed model, whose independent variables are volume and visibility. Then the paper uses200pcu as incremental unit to calculate average speed under different visibility.Finally, based on the average speed model and relationship between85%th speed and average speed, the paper derives a model to calculate speed limit value. Then the paper uses200pcu as incremental unit to calculate speed limit value under different visibility. Because the model is built on observed date, the speed limit valve calculated by model conforms well to practical traffic condition.