Car-Following Under Congested Conditions: Empirical Findings

Abstract

In traffic flow analysis several regimes are distinguished, such as congested and noncongested flow conditions. Indications exist that driving behavior differs by regime and that it may change discontinuously between regimes. In contrast most traffic flow models used today basically assume the same car-following behavior irrespective of the traffic flow regime. It is hypothesized that, because of this deficiency, these models do not always perform satisfactorily. To clarify this issue, differences in car-following between congested and noncongested flow are analyzed with data from two sites on Dutch freeways. It is shown that, at the same speeds, passenger car drivers follow with smaller headways in noncongested than in congested flow. Car-following of truck drivers does not show differences between regimes. Microscopic distance gap-speed models are established for several road-user classes, valid for each of the two flow regimes. To show the improvements resulting from these new microscopic relationships, the latter are implemented in a microscopic simulation model with which macroscopic patterns in traffic flow are modeled. The macroscopic findings produced with the regime-specific car-following rules show a considerable improvement in modeling performance.