Risk-Based Prioritization of Terrorist Threat Mitigation Measures on Bridges

This paper describes a risk-based methodology developed to facilitate prioritization of terrorist threat mitigation strategies on individual bridges. Numerous risk-based methods have been used for prioritization among a group of bridges or other assets. However, this methodology is unique in that it is specifically designed to focus on a single bridge and the risk associated with each of its many individual structural components. “Risk,” as discussed herein, describes the relative potential for a terrorist attack against a specific component and the associated consequence from the attack. It is based on such factors as the component’s importance to overall structural stability, its location and thus accessibility to terrorists, and its resistance to the specific threat. The component-specific risk factors and their modifying attributes are described. The result of the methodology is a rank-ordered list of components most at risk to an attack, allowing prioritization and optimization of the mitigation design for the bridge. Once mitigation schemes are identified, the methodology can then be utilized to recalculate mitigated risk, allowing for a direct indication of cost/benefit of the mitigation design. The methodology and comparison criteria are described and a simple application example is given to demonstrate the usefulness of the methodology.