Analyzing and Modeling of Expressway Traffic Characteristics near Ramps in Beijing 3rd Ring Road

Both on-ramps and off-ramps are typical bottlenecks in urban traffic system, where traffic congestions often appear. The system with an on-ramp and an off-ramp is regarded as the typical scenario to study the effect of the relative location of on-ramp and off- ramp. The system can be classified into two types, the case with an upstream on-ramp and that with a downstream on-ramp. CTM (Cell Transmission Model) is used to model the system and calibrated by the data from the Beijing 3rd ring road. The results show traffic flow characteristics in the two systems are far different. Especially, for the system with a downstream on- ramp, main road has the priority in the merge area, and CTM cannot describe traffic characteristics. Thus, by considering the priority, Mainline Priority CTM (MP-CTM) is presented to describe the characteristics. The simulation results suggest that MP- CTM fits the empirical data from Beijing 3rd ring road.