Abstract
The core functionality of many socio-technical systems, such as supply chains, (inter)national trade and human mobility, concern transport over large geographically-spread complex networks. The dynamical intertwining of many heterogeneous operational elements, agents and locations are oft-cited generic factors to make these systems prone to large-scale disruptions: initially localised perturbations amplify and spread over the network, leading to a complete standstill of transport. Our level of understanding of such phenomena, let alone the ability to anticipate or predict their evolution in time, remains rudimentary. We approach the problem with a prime example: railways. Analysing spreading of train delays on the network by building a physical model, supported by data, reveals that the emergence of large-scale disruptions rests on the dynamic interdependencies among multiple ‘layers’ of operational elements (resources and services). The interdependencies provide pathways for the so-called delay cascading mechanism, which gets activated when, constrained by local unavailability of on-time resources, already-delayed ones are used to operate new services. Cascading locally amplifies delays, which in turn get transported over the network to give rise to new constraints elsewhere. This mechanism is a rich addition to some well-understood ones in, e.g., epidemiological spreading, or the spreading of rumours and opinions over (contact) networks, and stimulates rethinking spreading dynamics on complex networks. Having these concepts built into the model provides it with the ability to predict the evolution of large-scale disruptions in the railways up to 30-60 minutes up front. For transport systems, our work suggests that possible alleviation of constraints as well as a modular operational approach would arrest cascading, and therefore be effective measures against large-scale disruptions.
Highlights
Socio-technical systems such as supply chains,national trade and human mobility provide pivotal support to modern societies
We find that these processes require a dynamical interplay among three building blocks: (a) constraints, (b) cascading, and (c) transport, wherein cascading playing the key role for delay amplification
In this paper we focus on railway transport with a wider outlook to transport and logistic systems at large, our work connects to a wider class of dynamical processes taking place on networks
Summary
Socio-technical systems such as supply chains, (inter)national trade and human mobility provide pivotal support to modern societies. Note that the above references include studies of multiple types of transport systems: airways, railways, supply chains, and even the analogy with freight truck and cargo ship transport All these systems share the common feature of scheme-based transport, where disruptions may lead to subsequent delay of other transport units [38,39,40,41]. Due to heterogeneity in terms of space, time, human interactions and externalities that impact the system, the existing models typically lack accuracy and predictability (of evolution dynamics) in cases other than ‘regular’
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