A discrete event traffic model explaining the traffic phases of the train dynamics in a metro line system with a junction

TL;DR

This paper introduces a mathematical discrete event model for metro train dynamics at a junction, enabling analysis of traffic phases and train frequency based on system parameters.

Contribution

It develops a Max-plus algebra-based model that analytically derives train frequency and traffic behavior in a metro system with a junction, advancing understanding of traffic physics.

Findings

Analytical expression for asymptotic train frequency.

Model captures effects of safety intervals and train distribution.

Provides insights for traffic control strategies.

Abstract

This paper presents a mathematical model for the train dynamics in a mass-transit metro line system with one symmetrically operated junction. We distinguish three parts: a central part and two branches. The tracks are spatially discretized into segments (or blocks) and the train dynamics are described by a discrete event system where the variables are the $k^{th}$ departure times from each segment. The train dynamics are based on two main constraints: a travel time constraint modeling theoretic run and dwell times, and a safe separation constraint modeling the signaling system in case where the traffic gets very dense. The Max-plus algebra model allows to analytically derive the asymptotic average train frequency as a function of many parameters, including train travel times, minimum safety intervals, the total number of trains on the line and the number of trains on each branch. This derivation permits to understand the physics of traffic. In a further step, the results will be used for traffic control.