Mobile source emission control cost-effectiveness: Issues, uncertainties, and results

Government agencies and private organizations often use cost-effectiveness, calculated in dollars per ton of emissions reduced for various control measures, to determine which control measures should be implemented to meet emission reduction requirements. Different studies may, however, yield significantly different, sometimes contradicting, results for the same control measures. The results differ because of the various calculation methodologies used and assumptions made about the values of costs and emission reductions. This paper examines some important methodological issues involved in calculating the cost-effectiveness of mobile source control measures and proposes appropriate methods for calculating cost-effectiveness. Included are such issues as using user costs or societal costs, using costs at the manufacturer or the consumer level, determining baseline emissions, using emission reductions in nonattainment or in both nonattainment and attainment areas, using annual or pollution-season emission reductions, considering multiple-pollutant emission reductions, and applying emission discounting. This paper then reviews methodologies used in 11 studies recently completed in the United States on the cost-effectiveness of mobile source control measures. On the basis of the methods proposed here for addressing the above issues, the original estimates in each study are modified to correct inconsistent or inappropriate methods so that the studies are comparable. From the adjusted results, the paper presents relative cost-effectiveness of 19 mobile source emission control measures.