Origin of synchronized traffic flow on highways and its dynamic phase transitions

TL;DR

This paper investigates how ramps influence highway traffic, revealing a new oscillatory state caused by ramp flux that leads to synchronized traffic flow, and models the transition as a subcritical Hopf bifurcation.

Contribution

It introduces a hydrodynamic model showing how ramp flux induces a new oscillatory traffic state and explains phase transitions as a Hopf bifurcation.

Findings

Presence of ramps creates a recurring hump state with oscillations.

The hump state is the origin of synchronized traffic flow.

Transitions between free flow and hump state are subcritical Hopf bifurcations.

Abstract

We study the traffic flow on a highway with ramps through numerical simulations of a hydrodynamic traffic flow model. It is found that the presence of the external vehicle flux through ramps generates a new state of recurring humps (RH). This novel dynamic state is characterized by temporal oscillations of the vehicle density and velocity which are localized near ramps, and found to be the origin of the synchronized traffic flow reported recently [PRL 79, 4030 (1997)]. We also argue that the dynamic phase transitions between the free flow and the RH state can be interpreted as a subcritical Hopf bifurcation.