The National Renewable Energy Laboratory (NREL) is managing a series of light duty vehicle chassis dynamometer emissions tests on alternative fuel vehicles for the U.S. Department of Energy (DOE). This testing program is part of a larger demonstration of alternative fuel vehicles that was mandated by the Alternative Motor Fuels Act of 1988 (AMFA). As part of the AMFA program, light duty vehicle performance, operational costs, maintenance, and fuel economy are also being collected by NREL's Alternative Fuels Utilization Program staff and disseminated through the Alternative Fuels Data Center (AFDC).In Phase 1 of the AMFA emissions test program (AMFA I), 18 vehicles were tested by three laboratories. All the vehicles tested under AMFA I were 1991 model year. In Phase 2 of the program (AMFA II), the number of vehicles was increased to nearly 300, including M85 Dodge Spirits, E85 (85% ethanol, 15% gasoline) Chevrolet Luminas, and compressed natural gas (CNG) Dodge passenger vans. Each of these vehicles is to be tested at odometer readings of 4,000; 10,000; 20;000; and subsequent intervals of 10,000 miles. Flexible or variable fuel vehicles are being tested on three test fuels, including 85% alcohol/15% gasoline, 50% alcohol/50% gasoline, and reformulated gasoline. All the AMFA II vehicles are 1992-1994 model year.Phase II testing includes a Federal Test Procedure (FTP) test, followed by two of the EPA's Inspection/Maintenance (I/M240) tests. The I/M240 tests were intended for use as criteria for deciding whether to retest vehicles. The tests were also used to begin developing a data base to determine if the less-expensive I/M240 could substitute for the FTP in future emissions testing.Considering data from early results from the AMFA II testing, we looked at issues such as repeatability of the I/M240 and FTP tests and the correlation of the I/M240 to the FTP test. We concluded that the I/M240 test is not an appropriate comparison to the FTP Further, the I/M240 test is not as reliable as the FTP in estimating the “real world” emissions of these relatively low-emission vehicles.