On the Spatial Evolution of Traffic State Transitions: Empirical Observations and General Features

Abstract

Features of transitions between stationary traffic states for both congestion onset and dissipation were evaluated through empirical observations at two freeway sites. Results reveal that transition durations vary significantly between sites and that they can be rather long, with observed average transition durations of 42–45 min in one site. It was also observed that transition durations remain relatively constant within a queue, while transition rates vary as the transition zone travels upstream of the bottleneck. In addition, results also suggest that complex site geometry, particularly the presence of multiple lane reductions, has an effect on the spatial evolution of transition rates, while single merging and diverging maneuvers do not seem to affect the mechanism of transitions. Finally, it was observed that the presence of non-stationary traffic periods could have a considerable effect on the estimation of key traffic variables in locations where long transition durations are observed.