Test of Behavioral Theory of Multilane Traffic Flow: Queue and Queue Discharge Flows

Daganzo recently proposed a behavioral theory of multilane traffic flow. This theory is the basis for several predictions related to flow phenomena, including several about the way that the relative speeds and flows in different lanes change in transitions to and from congested flow. In particular, the theory asserts that the more aggressive drivers (referred to as “rabbits”) always behave so as to maximize their speed. In congested flow, speeds are assumed to be nearly equal for all the lanes, and rabbits distribute themselves across the lanes so as to maintain this equality of speed. In acceleration downstream from queues, the equality of speed among the lanes breaks down once the free-flow speed of the slowest lane is reached, and the rabbits segregate themselves in the fastest lane. This redistribution of flow is expected to lead to two distinct flow states in queue discharge: capacity flow and discharge flow. Because the transition from capacity flow to discharge flow may lead to different overall flows and densities in the two states, a wave marking the transition between them may move either upstream or downstream. Automatically collected flow, occupancy, and speed data from freeways in the San Diego and Toronto areas were used to test these features of the theory at merge bottlenecks and in queue discharge following the removal of incidents. It was found that there are often speed differences among the lanes even in congested flow and that sudden redistribution of flow across the lanes can occur without speed equalization. These findings imply that Daganzo’s behavioral logic is oversimplified and that something more than just maximization of speed by aggressive drivers is involved in the distribution of flow across the lanes.