A THEORY OF CONGESTED TRAFFIC FLOW

Based on recent results on observations of traffic flow dynamics, new hypotheses about properties of congested flow are proposed. In particular, it is proposed that: 1) there are no fundamental diagrams which may describe the whole multitude of homogeneous states of traffic flow; 2) there are no unstable homogeneous states of traffic flow with respect to infinitesimal fluctuations, i.e., there is no critical density for traffic flow - in the whole possible range of the vehicle density homogeneous states of traffic flow can exist; 3) the characteristic line of the jam's downstream front separates the whole multitude of states of traffic in the flow-density plane into two different classes: (i) states below this line are stable with respect to any fluctuations and (ii) states above this line are metastable states where the nucleation effect leading to local phase transitions can occur. It is also noted that there is a reserve in the increasing of the highway capacity of about 50%, if an occurrence of any jams would be prevented.