The comfortable driving model revisited: Traffic phases and phase transitions

TL;DR

This study revisits a microscopic traffic model to evaluate its ability to reproduce traffic phases and transitions, comparing results with empirical data and Kerner's three-phase traffic theory.

Contribution

It demonstrates that the model can qualitatively reproduce three traffic phases and transition patterns, using a rule-based classification method, despite theoretical discrepancies.

Findings

The model reproduces free flow, synchronized traffic, and wide moving jams.

Transitions from free flow to jams often involve an intermediate synchronized phase.

The F->S transition is more likely than a direct F->J transition.

Abstract

We study the spatiotemporal patterns resulting from different boundary conditions for a microscopic traffic model and contrast it with empirical results. By evaluating the time series of local measurements, the local traffic states are assigned to the different traffic phases of Kerner's three-phase traffic theory. For this classification we use the rule-based FOTO-method, which provides `hard' rules for this assignment. Using this approach, our analysis shows that the model is indeed able to reproduce three qualitatively different traffic phases: free flow (F), synchronized traffic (S), and wide moving jams (J). In addition, we investigate the likelihood of transitions between the three traffic phases. We show that a transition from free flow (F) to a wide moving jam (J) often involves an intermediate transition; first from free flow F to synchronized flow S and then from synchronized flow to a wide moving jam. This is supported by the fact that the so called F->S transition (from free flow to synchronized traffic) is much more likely than a direct F->J transition. The model under consideration has a functional relation between traffic flow and traffic density. The fundamental hypothesis of the three-phase traffic theory, however, postulates that the steady states of synchronized flow occupy a two-dimensional region in the flow-density plane. Due to the obvious discrepancy between the model investigated here and the postulate of the three-phase traffic theory, the good agreement that we found could not be expected. For a more detailed analysis, we also studied the vehicle dynamics at a microscopic level and provide a comparison of real detector data with simulated data of the identical highway segment.