An investigation was made of the feasibility of controlling exhaust emissions through a program of mandatory vehicle inspection and maintenance. Exhaust emission quantities, i.e., levels and reductions, were estimated based on a constant volume sampling (CVS) procedure. The most cost-effective inspection interval is approximately yearly regardless of the inspection/maintenance procedures applied. Inspection procedures performed in a state lane using the measurement of emission levels under load are generally more cost-effective than those performed in franchised garages using conventional diagnostic instruments, but produce smaller emission reductions. A statistical analysis of the emission reductions for the baseline and test fleets has revealed that the predicted differences in mean emission levels is significant at greater than the 90 percent level of confidence. Emission reductions are most sensitive to the inspection approach used to reject vehicles and to the extent of the imposed maintenance. (Author)