Critical infrastructure systems provide services that are essential to both the economy and wellbeing of nations and their citizens. As documented in a recent report to the U.S. Congress (U.S. General Accounting Office, 2001), it is of vital importance that these services not be degraded, whether by willful acts such as terrorism or by natural or random events such as earthquakes, design flaws or human error. Yet infrastructure systems and the organizations that manage them are now recognized as components of highly-coupled systems that increasingly rely on one another in order to deliver key services. In, addition, as complex, interconnected systems, they are vulnerable to disruptive events that propagate from system to system. The September 11, 2001 attack on the World Trade Center (WTC) in New York City illustrates the importance of understanding relationships among infrastructure systems and of managing these relationships in order to ensure continuance of necessary services following disruptive events. This research is intended to improve understanding of and support for the management of critical infrastructure interdependencies following large-scale, disruptive disasters. As discussed more fully below, infrastructure interdependencies occur when, due to either geographical proximity or shared operations, an impact on one infrastructure system is also an impact on one or more other infrastructure systems. The particular focus of this work is on developing techniques that can be used either to mitigate against or respond to events that have the capability 1

Abstract — Modern society depends on the operations of civil infrastructure systems, such as transportation, energy, telecommunications and water. Clearly, disruption of any of these systems would present a significant detriment to daily living. However, these systems have become so interconnected, one relying on another, that disruption of one may lead to disruptions in all. The focus of this research is on developing techniques which can be used to respond to events that have the capability to impact interdependent infrastructure systems. As discussed in the paper, infrastructure interdependencies occur when, due to either geographical proximity or shared operations, an impact on one infrastructure system affects one or more other infrastructure systems. The approach is to model the salient elements of these systems and provide decision makers with a means to manipulate the set of models, i.e. a decision support system. 1

Abstract: This study investigates impacts of the 2001 World Trade Center attack on critical infrastructure systems in the New York City metropolitan area. Of particular interest are the physical or logical connections—also known as interdependencies—among these systems, and the impacts of the attack on them. This study extends knowledge about the behavior of complex and interdependent infrastructures systems following a significant disruption. The results depict impact to all infrastructure systems as a result of the attack, with disruptions reported throughout the 3 month study period. Approximately 20 % of these disruptions involved interdependencies, and a majority of infrastructure systems were involved in at least one interdependency. The results therefore suggest that interdependence is a pervasive condition of New York City’s critical infrastructures. Accordingly, approaches to planning for and managing infrastructure-related disruptions, particularly those involving interdependency, are discussed.

Critical infrastructure systems provide services that are essential to both the economy and well-being of nations and their citizens. As documented in a recent report to the U.S. Congress (U.S. General Accounting Office, 2001), it is of vital importance that these services not be degraded, whether by willful acts such as terrorism or by natural or random events such as earthquakes, 166 Managing Disruptions to Critical Infrastructures design flaws, or human error. Yet infrastructure systems and the organizations that manage them are now recognized as components of highly coupled systems that increasingly rely on one another in order to deliver key services. In addition, as complex, interconnected systems, they are vulnerable to disruptive events that propagate from system to system. The September 11, 2001, attack on the World Trade Center in New York City illustrates the importance of understanding relationships among infrastructure systems and of managing these relationships in order to ensure continuance of necessary services after disruptive events. This research is