for example, the real-life restructuring of California’s electricity industry demonstrated linked and unexpected effects. Fuel production, refining, and distribution were disrupted, sometimes cutting off fuel supplies to the very plants that should have been generating their electricity. Interruptions in water distribution affected the state’s agribusiness. Soaring wholesale power prices had rippling regional effects. In Washington state, salmon-protection and air-quality regulations had to be relaxed and aluminum mills shut down. Idaho farmers curtailed potato production to exploit Idaho Power Company’s electricity buy-back program.

This paper focuses on the tension between the need to push our civil infrastructure systems to higher levels of efficiency and competitiveness and the need to ensure minimum levels of service, reliability, and security, even under critical conditions. To set the scene, some recent history is given, and infrastructure systems are described in terms of their performance, interdependencies, and vulnerabilities. This is followed by a description of some emerging frameworks that promise to capture these “systems of systems” and their interdependencies. A case study is presented highlighting the benefits of exploiting interdependencies, and research challenges are identified.

INFRASTRUCTURE INTERDEPENDENCIES

Infrastructure interdependencies appeared on the radar screens with Presidential Decision Directive 63 (PDD-63) on Critical Infrastructure Protection. Prompted by the Oklahoma City bombing in 1995 and the 1996 Defense Science Board Task Force on Information Warfare, PDD-63 was the culmination of a 15-month study by the President’s Commission on Critical Infrastructure Protection, which revealed the rapidly growing capability of exploiting energy, banking and finance, transportation, vital human services (water, wastewater, and health services), and telecommunications infrastructures, especially through digital infrastructures (PDD-63, 1998). The directive acknowledged that our national and economic security depend on the critical infrastructures and information systems that support them. To ensure their reliability and protection, committees were established for each infrastructure sector and paired with their agency counterparts to study sector-specific problems. These initiatives have focused on protecting information systems against malicious intrusions (cyber attacks) that could cause the banking, finance, power systems, and other critical infrastructures to fail.

Infrastructure systems are also vulnerable to myriad stresses and failures as a result of everyday interdependencies, insufficiencies, and inefficiencies. Cascading power blackouts in the United States in July and August 1996 cost an estimated $1.5 billion, including related infrastructure and environmental impacts (Amin, 2000). On a grander scale, recent estimates of the annual cost to the U.S. economy from non-cyber power disturbances exceed $119 billion, most of which is related to disruptions to discrete manufacturing and electricity-dependent utilities



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