Access the full research article for free:
http://www.infrastructure-complexity.com/content/2/1/1

Research just published by experts in the Centre for Earth Systems Engineering Research, working with Southampton University have shown how permutable infrastructure components can reduce the risks of cascading failures.

The inter-connected and complex nature of modern infrastructure systems has created a “network of networks” that, when disrupted by deliberate action, or natural hazard event, can result in cascading failure that leads to the complete fragmentation of all connected systems from the destruction of a comparatively small number of nodes.

Existing “network of networks” approaches are still in infancy and have shown limits when trying to model the robustness of real-world systems, due to simplifying assumptions regarding network interdependencies and post-attack viability.

This work challenge such assumptions and demonstrates, through simulation, how failure to represent certain infrastructure properties can lead to inappropriate, or counterproductive, network adaptation and protection strategies in many circumstances.

1. Most assessments to date have assumed that in the event of a cascading failure only the largest single contiguous part of a network remains viable.  Whilst this measure is of some use, it fails to recognise that merely isolating infrastructure components does not necessarily mean they fail.  For example, dry roads within a town that has been cut off by floodwater, will still function even if the roads into the town do not.
2. It is possible to influence the nature of the failure propagation between coupled networks by allowing nodes in a given network to have multiple supporting nodes in another network.  For example, providing a back up power supply.
3. Previous studies have shown that removing interdependent links reduces the chance of cascading failure.  However, we find that this is counterproductive when you consider the nature of infrastructure systems and that one infrastructure network often requires a certain degree of interdependence with another in order to be viable..  For example, flooding of a road network may impact our ability to access railway stations, having a knock-on impact upon train use.  Obviously, removing all road-rail connections will ensure the rail network does not receive a minimum amount of passengers, goods, and personnel in order to operate.

Finally, we propose the use of permutable or adaptable systems as efficient and effective mechanisms to give network of network systems rewiring capabilities.  These permutable nodes and links appear to protect coupled networks from the destructive consequences of isolation and cascading failure and at the same time preserve network resources by limiting the amount of redundancy needed to absorb a disturbance.  These permutable systems are different from multi-service conduits.  For example, an electric line that carries phone communications at the same time would propagate failure through both phone and electricity networks in case of malfunction while, on the other hand, components that can provide alternated states of coupling to different networks limit the topological propagation of cascading failure while providing an alternate configuration to the system because of their rewiring capabilities.  Examples include roads convertible to landing strips, tunnels that can alternate between traffic and storm water management (e.g. the Stormwater Management and Road Tunnel (SMART) in Kuala Lumpur), energy storage devices on board electric vehicles that can be plugged to the power grid when not in use so as to store and produce energy whenever needed.

Read the full article for free:
Khoury M, Bullock S, Fu G, and Dawson RJ (2015) Improving measures of topological robustness in networks of networks and suggestion of a novel way to counter both failure propagation and isolation, J. Infrastructure Complexity, 2(1):1-20.