The Traffic Phases of Road Networks

TL;DR

This paper analyzes the fundamental diagram of traffic flow in road networks, identifying four main phases and exploring how junction management and control strategies influence traffic dynamics and efficiency.

Contribution

It introduces a comprehensive analysis of traffic phases in road networks, including the effects of junction management and control strategies, with analytical approximations and extensions to complex city layouts.

Findings

Four main traffic phases identified in road networks.

Traffic light controls can improve traffic flow and reduce congestion.

Junction size significantly affects traffic slowdown at intersections.

Abstract

We study the relation between the average traffic flow and the vehicle density on road networks that we call 2D-traffic fundamental diagram. We show that this diagram presents mainly four phases. We analyze different cases. First, the case of a junction managed with a priority rule is presented, four traffic phases are identified and described, and a good analytic approximation of the fundamental diagram is obtained by computing a generalized eigenvalue of the dynamics of the system. Then, the model is extended to the case of two junctions, and finally to a regular city. The system still presents mainly four phases. The role of a critical circuit of non-priority roads appears clearly in the two junctions case. In Section 4, we use traffic light controls to improve the traffic diagram. We present the improvements obtained by open-loop, local feedback, and global feedback strategies. A comparison based on the response times to reach the stationary regime is also given. Finally, we show the importance of the design of the junction. It appears that if the junction is enough large, the traffic is almost not slowed down by the junction.