Study On Variable Speed Limit Control Strategy Of An Urban Expressway

In recent years, with the deterioration of urban traffic, urban expressway has gradually become one of methods to solve traffic problems. However, the number of motor vehicles is increasing at such a rapid speed that lead to the decrease of velocity, increase of fuel consumption, serious air pollution and low operation efficiency. More and more researchers have focused on urban expressway management control. At present, the study of urban expressway management is mainly about the building principle of urban expressway infrastructure, traffic flow guidance system, ramp control etc. The study of variable speed limit for urban expressway is still at initial stage. Therefore, how to design reasonable strategies and speed limit values to provide safe, fast, and efficient operation of the urban expressway according to the traffic conditions are the topic of this research.This thesis aims to analyze the traffic characteristics on urban expressway and establish variable speed limit model during night hour, off-peak hour, peak hour, and accident period, which lay the foundations for determine the speed limit value.To this end, strategies and implementations of variable speed limit are reviewed. The pros and cons of existing models are summarized. Then, the RTMS and GPS data are processed to analyze the spot speed, volume, spot speed-volume relationship and different vehicles’ running speed. The traffic characteristics should be considered when designing variable speed limit model and the implementation of variable speed limit shouid based on section, time of day, the type of vehicle, and speed limit on lane.During night and off-peak hour, models to reflect the transport efficiency and relationship between fuel consumption and speed are established. The objection function on minimizing transport cost and fuel consumption is formulated to to solve the variable speed limits. During peak hour, traffic flow model is used and factors which impact traffic flow parameters are analyzed in this thesis. The sections are divided into three parts which are the bottleneck sections, the upstream, and downstresm sections. Methods to calculate the speed limit of each section are proposed. During accident period, in order to reduce secondary accidents, methods to calculate speed limit on the section of incident and upsteam are poposed. A case study of Beijing urban expressway is used to calculate the speed limit during different period.Finally, based on the traffic simulation software VSSIM, Beijing West Third Ring Road Platform is built. The effect of variable limit speed is evaluated. The results show that the variable speed limit can reduce the discreteness of speed and improve the safety of the road.