ANOTHER LOOK AT IDENTIFYING SPEED-FLOW RELATIONSHIPS ON FREEWAYS

Despite approximately 50 years of research on highway operating characteristics, the way in which the speed-flow relationship moves between free flow and congested flow conditions is still not clearly understood. The speed-flow relationship as it pertains to those transitions is investigated using an extensive data set collected on the Queen Elizabeth Way freeway in Ontario. Two different analytical approaches are used: time-connected plots of mean speed and mean flow and an event-based trace, averaged with respect to the transition to and from congested flow. The results confirm several aspects of conventional understanding but also raise questions that are hard to answer with the conventional interpretations of speed-flow relationship.