The relationship between vehicle emissions control program features and vehicle emissions

The automobile has become a formidable human health and welfare problem. Much work has been done studying the effects of automobile exhaust emissions. It is clear that large scale corrective action is required to mitigate this problem.; In order to help meet air quality standards, the Federal government has required states and localities with excessive automotive emissions to implement motor vehicle emission control inspection and maintenance (I/M) programs. These I/M programs have been designed in various ways according to individual state and locality preferences. The problem with these many program designs lies in determining which programs work best. A study was needed to develop a method to make this determination.; The objective of this study was to compare selected I/M programs representing the broadest possible scope of existing designs. Data relating to I/M program design and vehicle emissions were analyzed. The major source of this data was the United States Environmental Protection Agaency (USEPA). Data was collected by the National Center for Vehicle Emissions Control and Safety (NCVECS), located at Colorado State University.; Fifteen cities were studied. Nine of these had I/M programs while six did not. The non-I/M cities were used as a control group. Comparisons were made among the I/M cities and non-I/M cities.; A total of ten hypotheses were formulated and tested. Several different statistical tests were employed for the analyses.; Results of the study showed that some of the differences among I/M program designs were related to differences in emissions from vehicles surveyed in those I/M program locations. Other design differences however, were not related to emissions.; Important findings of the study suggest the following relationships: (1) Centralized I/M programs appear to work somewhat better than decentralized I/M programs. (2) Registration enforced I/M programs appear to work better than windshield sticker enforced I/M programs. (3) I/M inspections consisting of a tailpipe exhaust measurement plus a visual inspection appear to work better than I/M inspections with only one of these components. (4) The length of time a particular I/M program was in operation did not appear to be related to its effectiveness.