Three-phase traffic theory and two-phase models with a fundamental diagram in the light of empirical stylized facts

TL;DR

This paper compares three-phase traffic theory with two-phase models, showing that similar traffic patterns can be reproduced by both, and emphasizes the importance of precise terminology and model-data comparison for understanding traffic congestion.

Contribution

It demonstrates that two-phase models can replicate three-phase traffic patterns when parameters and real-world factors are properly considered, bridging the gap between the theories.

Findings

Both models can reproduce empirical traffic patterns.

Model parameters and real-world factors influence traffic pattern reproduction.

Clarifying terminology can reduce controversy in traffic modeling.

Abstract

Despite the availability of large empirical data sets and the long history of traffic modeling, the theory of traffic congestion on freeways is still highly controversial. In this contribution, we compare Kerner's three-phase traffic theory with the phase diagram approach for traffic models with a fundamental diagram. We discuss the inconsistent use of the term "traffic phase" and show that patterns demanded by three-phase traffic theory can be reproduced with simple two-phase models, if the model parameters are suitably specified and factors characteristic for real traffic flows are considered, such as effects of noise or heterogeneity or the actual freeway design (e.g. combinations of off- and on-ramps). Conversely, we demonstrate that models created to reproduce three-phase traffic theory create similar spatiotemporal traffic states and associated phase diagrams, no matter whether the parameters imply a fundamental diagram in equilibrium or non-unique flow- density relationships. In conclusion, there are different ways of reproducing the empirical stylized facts of spatiotemporal congestion patterns summarized in this contribution, and it appears possible to overcome the controversy by a more precise definition of the scientific terms and a more careful comparison of models and data, considering effects of the measurement process and the right level of detail in the traffic model used.