A tale of two cities. Vulnerabilities of the London and Paris transit networks

TL;DR

This study compares the resilience of London and Paris transit networks to failures and attacks, revealing critical vulnerabilities and minimal strategies that can cause systemic breakdowns using complex network theory.

Contribution

It introduces a comparative analysis of two major transit networks using complex network theory to identify vulnerabilities and minimal attack strategies impacting overall connectivity.

Findings

Less than 0.5% of stations can cause network collapse

Identified high-impact minimal attack strategies

Resilience correlates with specific network criteria

Abstract

This paper analyses the impact of random failure or attack on the public transit networks of London and Paris in a comparative study. In particular we analyze how the dysfunction or removal of sets of stations or links (rails, roads, etc.) affects the connectivity properties within these networks. We show how accumulating dysfunction leads to emergent phenomena that cause the transportation system to break down as a whole. Simulating different directed attack strategies, we find minimal strategies with high impact and identify a-priory criteria that correlate with the resilience of these networks. To demonstrate our approach, we choose the London and Paris public transit networks. Our quantitative analysis is performed in the frames of the complex network theory - a methodological tool that has emerged recently as an interdisciplinary approach joining methods and concepts of the theory of random graphs, percolation, and statistical physics. In conclusion we demonstrate that taking into account cascading effects the network integrity is controlled for both networks by less than 0.5 % of the stations i.e. 19 for Paris and 34 for London.