Phase Transition Model Based on Driver Reaction Time and Sensitivity

A fundamental diagram has great significance for traffic flow studies. An empirically obtained fundamental diagram shows widely scattered points of density–flow and traffic hysteresis phenomena. The scattering of a fundamental diagram with driver reaction time and sensitivity is explained. A simple phase transition model is presented. It is shown that driver reaction time primarily determines the direction of the density–flow transition path. The convexity or concavity of the density–flow transition path is affected by the sensitivity of a following vehicle. The traffic hysteresis, which represents the existence of two congested branches in the fundamental diagram, is also explained with driver reaction time and sensitivity.