Probabilistic Traffic Flow Breakdown In Stochastic Car Following Models

Dominic Jost
Dept.Computer Science, ETH Zürich, CH-8092 Zürich, Switzerland
Telephone: +41 1 632 2754
Fax: +41 1 632 1374
E-mail: djost@student.ethz.ch

Kai Nagel
Dept.Computer Science, ETH Zürich, CH-8092 Zürich, Switzerland
Telephone: +41 1 632 2754
Fax: +41 1 632 1374
E-mail: nagel@inf.ethz.ch

Submission date: Nov 15, 2002

Corresponding author: Kai Nagel

Number of words: 7500

Zusammenfassung:

There is discussion if traffic displays multiple phases (e.g.laminar, jammed, synchronized) or not. This paper presents computational evidence that a stochastic car following model, by changing one of its parameters, can be moved from having two phases (laminar and jammed) to having only one phase. Models with two phases show three states: two being homogeneous states corresponding to each phase, and a third state which consists of a mix between the two phases (phase coexistence).
Although the gas-liquid analogy to traffic models has been widely discussed, no traffic-related model ever displayed a completely understood stochastic version of that transition. Having a stochastic model is important to understand the potentially probabilistic nature of the transition. Most importantly, if indeed 2-phase models describe certain aspects correctly, then this leads to predictions for breakdown probabilities. Alternatively, if 1-phase models describe these aspects better, then there is no breakdown. Interestingly, such 1-phase models can still allow for jam formation on small scales, which may give the impression of having a 2-phase dynamics.