INTRODUCTION AND SUMMARY This report summarizes a study of the economic effectiveness of mandatory vehicle inspection and maintenance which was conducted as part of the Emission Test Program. The primary objectives of this study were twofold: 1) To analyze the cost-effectiveness of mandatory vehicle inspection and maintenance as a means for reducing automobile exhaust emissions. 2) To evaluate the regional implications of various inspection and maintenance procedures and to identify the most attractive procedures for a given class of air quality problems. The main thrust of the analysis was to determine the costs and emission reductions achieved using a number of candidate procedures. The information presented herein reflects the latest available experimental data@ including the results from the emission deterioration study@ as well as the most recent refinements to the economic effectiveness model. The study was conducted using a model which is capable of evaluating the performance characteristics and costs associated with a wide range of inspection and maintenance procedures. To support the model@ vehicular test data were obtained which defined the general maintenance state of vehicle populations@ the sensitivity of exhaust emissions to engine malfunctions@ the ability of service organizations to perform specific engine maintenance@ and the rate with which exhaust emissions and engine adjustments deteriorate with vehicle use. In keeping with the growing interest in vehicle inspection and maintenance a number of different procedures were examined in some detail. These included: ? Mandatory inspection and maintenance Engine inspection Emission inspection ? Mandatory maintenance only ? A hybrid inspection and maintenance procedure which involves a combination of the two previous processes