Emission tests were performed on a sample of light-duty trucks operating in Denver, Phoenix, Los Angeles and St. Louis. A total of 1,495 vehicles were tested: 375 in Denver, Phoenix and Los Angeles, and 370 in St. Louis. Model years 1975 through 1979 were tested in all cities. The St. Louis sample also included twenty diesel-powered trucks. The purpose of this program was to gather information for use in calculations and projections of air quality, a review of the EPA Vehicle Certification process and evaluation of current and possible vehicle Inspection/Maintenance programs. The St. Louis vehicles were subjected to the 1979 Federal Test Procedure with methane measurement, the EPA Highway Fuel Economy Test, the Federal Short Cycle Test, the Two Speed Idle Test and the Federal Three Mode Test. In addition, modal tests using the Surveillance Driving Sequence were performed on 166 vehicles including the diesel powered trucks. The Evaporative Emission Test using the SHED Technique was performed on 100 vehicles. Twenty-five vehicles also underwent an additional test sequence under low temperature conditions. This was comprised of a replicate 1979 Federal Test Procedure, Highway Fuel Economy Test and the Three Short Tests. The vehicles tested in Denver, Phoenix and Los Angeles were subjected to only the Two-Speed Idle Test and the Federal Three-Mode Test.