Infrastructure resilience for high-impact low-chance risks

Infrastructure resilience is the ability of an infrastructure system to withstand or recover quickly from difficult conditions, which in turn requires a detailed understanding of vulnerability and risk. But while designing for foreseeable risks is a challenge, accounting for risks that are difficult or even impossible to foresee - such as those arising from complex interdependent processes - poses a far greater challenge. This paper argues that civil engineers need a way of addressing such low-chance but potentially high-impact risks if they are to deliver truly resilient infrastructure systems. They need to cultivate a wisdom to admit what they genuinely do not know, and to develop processes to manage emerging unforeseeable consequences. A generalised vulnerability theory that can be applied to any infrastructure system is described, together with an example of how it can be applied to an urban transport network.