Phase diagram of traffic states in the presence of inhomogeneities

We present a phase diagram of the different kinds of congested traffic that are triggered by disturbances when passing ramps or other spatial inhomogeneities of a freeway. The simulation results obtained by the nonlocal, gas-kinetic-based traffic model are in good agreement with empirical findings. They allow one to understand the observed transitions between free and various kinds of congested traffic, among them localized clusters, stop-and-go waves, and different types of "synchronized" traffic. We also give analytical conditions for the existence of these states which suggest that the phase diagram is universal for a class of different microscopic and macroscopic traffic models. [S0031-9007(99)09232-7].