ORIGIN OF SYNCHRONIZED TRAFFIC FLOW ON HIGHWAYS AND ITS DYNAMIC PHASE-TRANSITIONS

We study the traffic flow on a highway with ramps through numerical si mulations of a hydrodynamic traffic flow model. It is found that the p resence of the external vehicle Aux through ramps generates a new stat e of ''recurring humps''(RH. This novel dynamic state is characterized by temporal oscillations of the vehicle density and velocity which ar e localized near ramps, and found to be the origin of the synchronized traffic flow reported recently [Kerner and Rehborn. 79, 4030 (1997)]. We also argue that the dynamic phase transitions between the free flo w and the RH state can be interpreted as a subcritical Hopf bifurcatio n.