Study On The Influence Rules Of Severe Weather On Traffic State Of Urban Expressway Networks

Severe weather is one of the most frequent natural disasters, in recent years, frequent traffic congestion and large area network paralysis accidents have been caused due to the severe weather like snow and rainfall. In the urban road transport system, the urban expressway networks undertake the main daily-motor vehicle traffic. Thus, studying the spatial and temporal distribution of the traffic state of urban expressway networks under severe weather condition and obtaining the occurrence and propagation rules of traffic congestion, has great significance for alleviating the traffic congestion and avoiding large area networks paralysis under severe weather.This paper was selected from the National Natural Fund. Firstly, the severe weather’influence on the road networks’traffic state was analyzed and corresponding research results of the current experts were summarized, by deeply dissecting the severe weather’s effects on the constituent three elements and road traffic flow characteristic parameters of urban road transport system. Secondly, vehicle speed was standardized based on the maximum speed limit, speed performance indicators were proposed to divide road section traffic state and the road networks’spatial and temporal traffic state evaluation system was established. Also, the evaluation indicators of road networks’ traffic state for different weather conditions were compared based on the sample data of Beijing expressway, thus, the spatial and temporal variation rules of the traffic state for urban expressway networks under severe weather can be obtained. Lastly, for the traffic congestion state, the network congestion originated road section recognition model based on tree structure was established, and congested road section recognition database was set up based on the platform of Oracle database. Based on the above analyses, the fixed and random traffic bottleneck sections, and the caused congestion’s spatial spread degree of Beijing expressway networks under severe weather can be got. The conclusions find that:from the time perspective, the severe weather has a greater influence on the traffic state of road networks between 6:00 to 22:00, with the increase of rainfall (snowfall), the severe weather sees a greater influence. From the space perspective, the congested road sections spread from the 3rd ring road to the whole networks, and the spread degree for workdays performs more significant than holidays under snow and rainfall. Meanwhile, random traffic bottlenecks will arise due to snow and rainfall and spread over the east, west and north areas of expressway networks, which locate in Haidian and Chaoyang Districts for the most bottlenecks. The spatial spread range of road sections congestion shows a discrete distribution within one hour, for workdays and holidays, the spread range is between 100km to 1000km and 100km to 900km respectively.