Zero range model of traffic flow

TL;DR

This paper models traffic flow using a zero-range process, providing analytical insights into traffic jam formation, phase separation, and metastability in a stochastic multi-cluster system.

Contribution

It introduces a zero-range process model for traffic flow, deriving critical densities and metastable states, and connects traffic jam formation to condensation phenomena in driven systems.

Findings

Identified critical density for phase separation in traffic flow.

Derived metastable homogeneous states above critical density.

Estimated nucleation times and critical cluster sizes for traffic jams.

Abstract

A multi--cluster model of traffic flow is studied, in which the motion of cars is described by a stochastic master equation. Assuming that the escape rate from a cluster depends only on the cluster size, the dynamics of the model is directly mapped to the mathematically well-studied zero-range process. Knowledge of the asymptotic behaviour of the transition rates for large clusters allows us to apply an established criterion for phase separation in one-dimensional driven systems. The distribution over cluster sizes in our zero-range model is given by a one--step master equation in one dimension. It provides an approximate mean--field dynamics, which, however, leads to the exact stationary state. Based on this equation, we have calculated the critical density at which phase separation takes place. We have shown that within a certain range of densities above the critical value a metastable homogeneous state exists before coarsening sets in. Within this approach we have estimated the critical cluster size and the mean nucleation time for a condensate in a large system. The metastablity in the zero-range process is reflected in a metastable branch of the fundamental flux--density diagram of traffic flow. Our work thus provides a possible analytical description of traffic jam formation as well as important insight into condensation in the zero-range process.