Transportation security and the role of resilience: A foundation for operational metrics

Abstract

This paper presents operational metrics to determine a passenger transportation system's resilience to terrorism. The metrics range from those specific to the number of trips to more holistic measures that include the contribution of these trips directly and indirectly to economic activity. These metrics can aid decision-makers in rendering more informed judgments about resource allocation and how to design a portfolio of security and recovery strategies. The paper also provides a framework for evaluating transportation risk, including the important role of perceptions in potentially amplifying these risks. It provides a range of strategies to promote resilience as well. Resilience of a transportation system is then quantified using the real-world case of the 2005 London subway and bus bombings. In terms of ordinary resilience, we find that 77.4 percent of total journey reductions on attacked modes were offset by increases in substitute modes for the 4 months following the attacks. We also estimate that 76.9 percent of total journey reductions on attacked modes were the result of a “fear factor,” as opposed to capacity reductions. The paper concludes with a set of proposed prospective resilience measures to evaluate the potential resilience of a transportation system. These metrics are based on the vulnerability, flexibility, and resource availability to cope with a terrorist attack or natural disaster.