Recent events have heightened our awareness of the vulnerability of civil infrastructure systems. Most of the research on this topic has focused on individual systems, while more recent efforts have recognized the interconnectedness of systems. Infrastructure systems have become so highly interconnected that a failure in one system can propagate through many systems and affect large geographic areas. The focus of this research is on reducing vulnerability by adding redundancy while taking into account the interdependencies of infrastructure systems.

The paper first presents background and definitions related to interdependent infrastructure systems. An algorithm is then presented that identifies vulnerabilities in the current and proposed designs due to interdependencies with other infrastructure systems. An illustrative case, the reliance of telecommunications on power, is used to demonstrate the practicality of the proposed procedure. The paper concludes with a discussion of further research, both theoretical and operational.