摘要：This paper examines the behavioral and stochastic aspects of modeling emissionreductions from vehicle Inspection and Maintenance (I/M) programs. Forecasts of thepotential emission reductions from such programs have been modeled by the use of theEnvironmental Protection Agency's MOBILE Model, EPA's computer model for estimatingemission factors for mobile sources. We examine the structure of this Model and review theway behavior of drivers, mechanics and state regulatory authorities is incorporated in thecurrent generation of the Model. We focus particularly on assumptions about vehicle repairunder I/M, compliance with I/M requirements, and the impact of test measurement error onpredicted I/M effectiveness. We also include some preliminary comparisons of the Model'soutcomes to results of the I/M program in place in Arizona. Finally, we perform somesensitivity analyses to determine the most influential underlying parameters of the Model.We find that many of the assumptions of the I/M component of the Model are basedon relatively small data sets on vehicle done in a laboratory setting, and that the output of theModel makes it difficult to compare the results against real world data from on-going stateprograms. In addition, the Model assumes that vehicles will either be repaired or receive awaiver. In the Arizona program there appears to be a third category of vehicles -- those whichfail the test and do not receive passes. This share may be as high as a third of all failingvehicles. Vehicles which do not eventually pass the test would be treated in the Model asnon-compliant. However, in current programs, states do not seem to be measuring andentering the compliance rate correctly. The paper also examines the evidence about whetheremissions deteriorate over the life of vehicle in a grams per mile basis (as assumed by theModel) or a grams per gallon basis. It finds support for the argument that emissionsdeteriorate on a grams per gallon basis.We find through sensitivity analysis that the repair effectiveness assumed by theModel to occur in an IM240 test are much greater than for the idle test, and that identificationrates and repair effectiveness vary a great deal according to the cutpoint. These results arebased on small numbers of vehicle tests in a laboratory setting and could be compared to realworld evidence. Examining costs and cost-effectiveness of variations in I/M programs isimportant for determining improvements in I/M programs. States may not have incentives todevelop cost-effective programs based on current Model that forecast emission reduction"credits" that are overly optimistic.
关键词：emission reduction; vehicle inspection and maintenance program
