Stability of multi-population traffic flows

TL;DR

This paper analyzes how mixed driver behaviors affect traffic flow stability on a ring-road, revealing critical thresholds for stability and the emergence of stop-and-go waves, which are not explained by single-population models.

Contribution

It provides an explicit computation of the critical penetration rate of stable drivers needed for stable traffic flow in multi-population models.

Findings

A small minority of aggressive drivers can destabilize traffic.

Stability depends on the number of cars, not just density.

Small experiments may lead to inaccurate stability conclusions.

Abstract

Traffic waves, known also as stop-and-go waves or phantom hams, appear naturally as traffic instabilities, also in confined environments as a ring-road. A multi-population traffic is studied on a ring-road, comprised of drivers with stable and unstable behavior. There exists a critical penetration rate of stable vehicles above which the system is stable, and under which the system is unstable. In the latter case, stop-and-go waves appear, provided enough cars are on the road. The critical penetration rate is explicitly computable, and, in reasonable situations, a small minority of aggressive drivers is enough to destabilize an otherwise very stable flow. This is a source of instability that a single population model would not be able to explain. Also, the multi-population system can be stable below the critical penetration rate if the number of cars is sufficiently small. Instability emerges as the number of cars increases, even if the traffic density remains the same (i.e. number of cars and road size increase similarly). This shows that small experiments could lead to deducing imprecise stability conditions.