The standard mass emission test (Federal Test Procedure) was performed for emission factors determination on samples of passenger cars operating in Los Angeles, Houston, Denver, Phoenix, St. Louis and Washington, DC. These samples were also used for obtaining abbreviated emission test (short cycle test), fuel economy test, emission related maintenance and other data. Two-thousand forty-two (2,042) vehicles were tested under the program. The FTP and the Highway Fuel Economy Test were performed on all vehicles at all sites. Some vehicles which exceed Federal standards (excluding the Houston site) were subjected to a restorative maintenance evaluation. The evaluation employed in Los Angeles was designed to address three-way catalyst technology. Some vehicles in all but the Los Angeles site were used to evaluate commercial repair facility performance in relation to idle speed and mixture adjustments. Other actions were taken in relation to each vehicle tested. These included an emission control system maladjustment/disablement and status inspection driveability evaluations and owner interviews to obtain vehicle maintenance and usage data.