Reproducibility of Flow–Density Relations in Heavily Congested Flow Based on Individual Vehicle Data

The flow-density relations represent equilibrium relations between flow and density in the stationary state. Using individual vehicle data, this paper extends to heavily congested flow the reproducibility of the flow-density relations found by Cassidy. A new filtering method using standard deviations of traffic variables in a vehicle group built from individual vehicle data is proposed to distinguish the nearly stationary state from the nonstationary state. The traffic data collected from the nearly stationary state with this filtering method show significantly smaller data scattering than do those without filtering in heavily congested flow, even though the data aggregation interval is kept at the same level. This fact indicates that a reproducible flow-density relation also exists in heavily congested flow if the traffic data are collected in the nearly stationary state