Analysis of maximum traffic flow and its breakdown on congested freeways

This study analyzes the dynamic behavior of traffic flow over time by deriving the theoretical value of flow oscillations convergence (F̃) following the breakdown of traffic flow. Modeling traffic flow fluctuations over time reflects two basic zones: the increasing demand zone that terminates approximately when the maximum flow is attained, and the oscillations zone that reflects the fluctuations of flow until its stabilization. The models in the flow-time plane introduce a new concept of “stable maximum flow” particularly for design purposes. Both converged values and observed recovery flow values represent the end of the recovery phase transition where the traffic stream approaches the free flow regime through lower flow conditions than the maximum flow conditions. A comparison between breakdown starting times and times of the maximum flow shows that in most cases, when one breakdown period (OB) is experienced, breakdown starts 21–50 min after observing the maximum flow. Modeling changes in traffic flows in the flow-time plane is emphasized for OB or multiple breakdown period (MBP) cases. The analysis of frequent OB and infrequent MBP cases allow for better controlling of the traffic flow by maintaining its flow level below maximum.