into play helps to ensure that decisions are consistent with public views and less likely to encounter the resistance embodied in the ''Not In My Backyard" response to infrastructure actions.

Considering Multiple Objectives

A fundamental feature of multi-objective problems is that there is no single, optimal solution. Instead, the focus of problem solving and decision making is finding a set of solutions that seem "better" than others, that is, they are not clearly dominated by any other, and exploring the tradeoffs among the objectives implied by choosing one of these "better" (i.e., nondominated, noninferior, efficient, or Pareto optimal) solutions over another. In other words, the measure of good infrastructure decision making is that no one can produce a clearly better plan of action.

Over the last 25 years, dozens of techniques have been developed for analyzing multi-objective problems.1 Rich in variety, reflecting the range of problems and decision contexts for which they were developed, the methods can be conveniently grouped into two categories: generating methods and preference-oriented methods.

As the name implies, generating methods are particularly useful for generating ''better" solutions to a problem. Their aim is to create either an approximation or exact representation of the set of nondominated solutions, which will form the basis for exploration of the tradeoffs among objectives. There is no attempt made to incorporate decision makers' preferences in any formal or explicit manner.

By contrast, preference-oriented use explicit quantitative statements of decision makers' preferences to identify a preferred solution (Cohon, 1978). Though preference-oriented techniques can help policy makers understand the implications of preferences and preference conflicts for decision making, many of them suffer from several disadvantages. They tend to reveal little information about the set of "better" solutions, thus limiting the insight gained from analysis. Also, they are rigid in the way preferences must be stated and are sensitive to characteristics of decision making processes typical of environmental problems. The presence of multiple decision makers can cause complications that defeat most of the preference-based methods.

A combination of methods often works best. A generating technique would be emphasized first to develop an appreciation of the range of choices and the tradeoffs. The planning workshop or design "charette" sometimes used for infrastructure planning is an example of a generating method.2 In reacting to the results generated, decision makers may be able to articulate preferences, for instance, a particular portion of the nondominated set worthy of further, detailed exploration.

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