Department of Geography
University of California, Santa Barbara CA 93106-4060
Phone 805 893 8992 Fax 805 893 8993 E-mail firstname.lastname@example.org
Systematic approaches to security investment decisions, from intelligence and surveillance to fortification, are crucial for sustainable homeland security. We describe analytical planning techniques to identify critical infrastructure, and to minimize the impacts of natural, accidental, and deliberate hazards.
Our initial approach to identifying critical infrastructure draws on location allocation theory. Specifically, we consider an existing service/supply system where user demands for service are entirely supplied by their closest facility. One metric of system performance is the total distance traveled by users, from demand points to supply points. The loss of one or more facilities due to some kind of interdiction forces the reassignment of users to more distant facilities. This results in increased total travel distance and time, and reduces overall system efficiency. Various interdiction strategies can be simulated to disable components of the supply system. In each case, demand is redistributed among the facilities, and it is therefore possible to measure the consequences of loss, and to determine the most damaging interdiction strategy.
At present the model assumes that interdiction of a facility disables it entirely, and that fortification completely prevents interdiction. The fortification/interdiction problem fits within the framework of a leader-follower or Stackelberg game, where the entity responsible for coordinating the fortification activity is the leader and the interdictor is the follower. The fortification planner must incorporate within his protection strategy a means of predicting the best response of the interdictor to his own actions. Small instances of the facility fortification/interdiction problem can be solved directly using commercial optimization software. However, problems of realistic size require more advanced solution techniques tailored to the specific mathematical structure of the problem. We propose both an exact algorithm, based on explicit enumeration, and a heuristic technique, which provides good approximate solutions when the use of exact methods becomes impractical. Several example fortification patterns are presented in detail, and demonstrate the degree to which different fortification patterns bar the detrimental effects of interdiction of the system. Recommendations for model extensions that incorporate probabilistic elements and different service/supply systems are also provided.
In summary, the aim of this study is to provide agencies with a mathematical tool which helps identify the optimal set of facilities to fortify, to hedge against the most disruptive interdiction of facilities. Protecting the most vulnerable facilities or predictable targets is not always the most cost-effective way of confronting threats. Fortification patterns which take into account the interdependency among the system components and the effect of multiple, simultaneous losses produce more sound and resilient protection plans.
The research has applications beyond military and homeland security. It enables system level planning — including physical protection but also everyday needs such as maintenance scheduling — for all kinds of critical infrastructure networks.
1 This research is funded by the U.S. Department of Transportation, Research and Special Programs Administration, and conducted by the National Consortium on Remote Sensing in Transportation — Infrastructure Management. Principal authors of the study are Richard Church and Paola Scaparra.