Many parts of the country have been in violation of the carbon monoxide and ozone National Ambient Air Quality Standards. Because of these violations, vehicle inspection and maintenance (I/M) programs have been implemented throughout the country. A method and procedure of evaluating the benefits of an I/M program as compared to the projected benefits designated in the MOBILE3 Emission Factor model has been developed. The method includes a detailed analysis of the individual operating parameters of an I/M program, such as the vehicle population, waiver procedures, and manual vs. automated analyzers. Evaluation of these parameters can assist agencies to compare benefits of their I/M programs to those projected in MOBILE3. This is of major importance, due to the requirements of the 1987 deadline for carbon monoxide and ozone attainment and the “reasonable extra efforts” program which undoubtedly will be required by EPA.