Traffic Speed-Flow Model for the Mix Traffic Flow on Beijing Urban Expressway

In order to explore the speed-flow relationship under complicated roadway characteristics and heavy traffic volume, this paper established a new practical model based on one month serial data collected from loop detectors on different sites of the expressway in Beijing. Different from the traditional model, the relationship formulated here is composed by free flow segment, stable flow segment and congested-evacuation segment. We start with a comprehensive review on classical speed-flow models. The limitation of general used model when analyzing the mixed traffic flow is pointed out. Then a cluster of new speed-flow models are established considering the site characteristics expressed with the distance from the bottleneck which appears at the entrance or exit ramp. Actual observed data shows fundamental parameters of speed-flow relationship model of urban expressway are affected by the entrance or exit ramp.