Terrorism risks for bridges in a multi-hazard environment

The paper will assess terrorist threats to bridge infrastructure and the cost-effectiveness of protective and counter-terrorism measures. This analysis will consider threat likelihood, cost of security measures, risk reduction and expected losses to compare the costs and benefits of protective measures to bridges to decide which protective measures are cost-effective. In this paper, a break-even cost-benefit analysis determines the minimum probability of a successful attack, absent the protective measures, that is required for the benefit of the protective measures to equal their cost. It was found that unless terrorist threat probabilities are high, then typical protective measures are not cost-effective. Bridges and other critical infrastructure are subject to a range of natural and man-made hazards, and terrorism is most likely not as important a threat as natural hazards. Economic risks due to terrorism are then compared with risks from flood and seismic hazards. It was found that economic risks to bridges from floods, earthquakes, and ship impact are significantly higher than threats from terrorism.