Percolation transition in dynamical traffic network with evolving critical bottlenecks

Abstract

A critical phenomenon is an intrinsic feature of traffic dynamics, during which transition between isolated local flows and global flows occurs. However, very little attention has been given to the question of how the local flows in the roads are organized collectively into a global city flow. Here we characterize this organization process of traffic as "traffic percolation," where the giant cluster of local flows disintegrates when the second largest cluster reaches its maximum. We find in real-time data of city road traffic that global traffic is dynamically composed of clusters of local flows, which are connected by bottleneck links. This organization evolves during a day with different bottleneck links appearing in different hours, but similar in the same hours in different days. A small improvement of critical bottleneck roads is found to benefit significantly the global traffic, providing a method to improve city traffic with low cost. Our results may provide insights on the relation between traffic dynamics and percolation, which can be useful for efficient transportation, epidemic control, and emergency evacuation.emergence | percolation | traffic T raffic, as a large-scale and complex dynamical system, has attracted much attention, especially on its dynamical transition between free flow and congestion (1-3). The dynamics of traffic have been studied using many types of models (4-11), ranging from models in macroscopic scales based on the kinetic gas theory or fluid dynamics to approaches in microscopic scales with equations for each car in the network. However, there is still a gap between the microscopic behavior of individual vehicles and the emergence of macroscopic city traffic. Indeed, a fundamental question has rarely been addressed: how the local flows in roads interact and organize collectively into global flow throughout the city network. This knowledge is not only necessary to bridge the gap between local traffic and global traffic, but also essential for developing efficient traffic control strategies.There are mainly two obstacles in studying how the collective network dynamics of real traffic emerge from local flows. The first obstacle is the lack of valid methods to quantify the dynamical organization of traffic in the road network. The second is the lack of data on traffic dynamics in a network scale. To overcome the first obstacle, we develop here a quantitative framework based on percolation theory, which combines evolving traffic dynamics with network structure. In this framework, instead of the commonly used structural topology, only roads in the network with speed larger than a variable threshold are considered functionally connected. In this way, we can characterize and understand the formation process of traffic dynamics.To overcome the second obstacle of missing data on a network scale and understand the organization processes of real traffic in a network, we collected and analyzed velocities of more than 1,000 roads with 5-min segments records measured in a road network in a cen...

An approach for evaluating connectivity of interrupted rail networks with bus bridging services

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