Investigation on traffic flow competition between main road and on-ramp on urban freeway

Bottlenecks at highway or urban freeway are one of origins of traffic congestion. Based on empirical investigation on traffic data collected from Beijing urban freeway, we find that when traffic is dense, upstream flow and ramp flow are correlated significantly. Competitions between the two flows at vicinities of several on-ramps during a morning peak are studied. Based on these empirical observations, a flow competition model as an extension of CTM (cell transmission model) is developed. The proposed model focuses on reproducing correlated upstream flow and ramp flow in dense traffic. Both empirical data and simulation results point out that several traffic phenomena, such as capacity drop and spontaneous traffic breakdown, can be explained as results of such a competition.