TRAFFIC PATTERNS IN UNSTABLE TRAFFIC FLOW ON FREEWAYS

To explain the different traffic patterns for very dense traffic on freeways like spreading shock fronts, irregular stop-start waves, bistability and hysteresis phenomena, a dynamic traffic model is presented. This model shows, depending on essentially two control parameters, the quoted variety of different traffic patterns. The patterns are derived as stationary profiles for regular stop-start waves and stable running shock waves and as transients approaching the stationary profiles as bifurcation with supercritical or subcritical dependence on the two control parameters, namely bottleneck capacity and mean density. Finally irregular motion examples are given. These irregularities are explained by means of chaos theory similar to the turbulence description of fluid motion. Freeway traffic control for dense traffic needs besides a traffic flow model advanced technologies for detection of section related traffic variables. As nonlocal measurement technique which uses a correlation method between neighboured measurement sites a mm-wave radar set up is described.