ABS has two advantages. First, ABS can represent CAS without resorting to inappropriate analytical models; at the same time, it can enable predictions of the desirability of different policy options. North (2000) developed a series of ABSs to explore pricing and various levels of competition with deregulated electric utilities. The simulations addressed the effects of price swings for natural gas, such as those that would follow a pipeline interruption; the number of companies needed for truly competitive markets; and the identification of companies colluding to drive up electricity prices.

Second, ABS may offer an improved control paradigm that can be implemented at the hardware level. With centralized control, infrastructure systems are vulnerable to the weakest link; distributed control can limit, localize, and allocate risk. Some models have been proposed whereby infrastructure system agents could automatically reconfigure a system to “heal” failures (Amin, 2000). Distributed control also enables distributed power generation, as well as the control of multiple infrastructure systems.

The meta-infrastructure system approaches described above are reasonably representative of the current state of the art. It is interesting to note that none of these frameworks deals explicitly with interdependencies induced by sharing input resources. Physical interdependencies in Rinaldi come the closest; Friesz et al. and Haimes and Jiang both use implicit notions of activity levels.

Interdependencies from resource sharing arise when improved efficiency is achieved by reducing redundancy across systems. When systems use resources completely independently of one another to provide their respective services, the systems are independent with respect to that resource, assuming perfect market competition. If the resources could have been shared but were not, the resources were redundant. Every reduction in redundancy in these systems through resource sharing creates a certain class of system interdependency.

Reduced redundancy, the elimination of a redundant power generator and high utilization of remaining generators, for example, can render a system more vulnerable. A beneficial example of resource sharing would be a hydropower facility and drinking water plant that use and reuse the same river flow to generate their respective services. In fact, the chief of the Bureau of Reclamation recently stated that to use water stored by 457 dams in the western United States as efficiently as possible water should be passed through the dams multiple times for recreation, power generation, and irrigation (WaterTech Online, 2001). Finally, tracking resource quantities explicitly would make possible more accurate assessments of the external costs (e.g., environmental impact) of using those resources.

CASE STUDY

Colorado Springs Utilities, an innovative western water utility that has been researching multiple uses of water resources, estimates the benefits would be worth more than $500,000 per year, not including windfalls from high electricity



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