impacts, whereas cost-effectiveness is an efficiency measure that quantifies the cost of achieving a unit of project effectiveness.1

Measuring the relative effectiveness of actual CMAQ projects did not prove feasible. The available data on the effectiveness of CMAQ projects are location specific; project data are valid only for the particular context and strategy involved. Sufficient data were not available on the effectiveness of similar strategies in several regions, making it difficult to generalize from particular project results or to compare types of projects systematically.

The committee decided to examine the literature for data on similar types of projects—primarily transportation control measures (TCMs)—and focused its review on project cost-effectiveness as requested in its charge. The committee selected cost per ton of emissions reduced as the primary cost-effectiveness measure by which to compare the pollution reduction potential of various strategies. The committee would have preferred as an effectiveness measure an indicator of the exposure of affected populations to various pollutant concentrations, and as a cost measure the total tangible and intangible costs to all segments of society, including both government agencies and users. A simple illustration explains why. Moving the position of exhaust stacks on public buses could reduce the exposure of affected populations, particularly those inside the bus, to particulate emissions, even though it would not change emission levels (Rodes et al. 1998). Thus, the project would show a positive impact if reducing exposure were used as the effectiveness measure, but it would have a neutral impact if reducing emissions were used. Unfortunately, the necessary data on neither exposure nor social costs were available. Moreover, the data on emissions were limited. Most of the studies report emission reductions for volatile organic compounds (VOCs) and nitrogen oxides


Cost-effectiveness analysis should not be confused with cost-benefit analysis, which requires that all costs and benefits be measured in monetary units so that each strategy can be compared on its own merits (i.e., whether the benefits are in excess of the costs) to answer the question of whether this strategy is the most worthwhile (from an efficiency perspective) that could be undertaken. Cost-effectiveness analysis normalizes effectiveness data—costs are expressed per unit of effectiveness—so that projects can be ranked to show which provide the greatest return for the investment made. For a more complete discussion of these analysis techniques, see Levin (1993).

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement