In 1999 DEQ submitted to the U.S. Environmental Protection Agency a short-term evaluation study of the Northern Virginia enhanced motor vehicle inspection and maintenance program. This study was a quantitative analysis of the emissions results from a six-month sample of program data. Addendum #1 of the study compares a subset of the Virginia data with data from a biennial, test-only ASM-2525 program in Connecticut. The Virginia program, which began in Spring 1998, uses the ASM-2 test (2525 and 5015 modes) on a biennial basis in a decentralized, test-and-repair network of approximately 365 stations. Vehicles older than 1981, 8,500 to 10,000 pounds gross vehicle weight rating, or four-wheel drive receive a two-speed idle test.
The study examined six months of emissions test results from 328,880 initial tests (about 25% of the Northern Virginia fleet) and corresponding retests. The overall initial test fail rate was 11.6%. Using a defined "measure of emissions reduction," the report concluded that the Virginia ASM-2 program provides emissions reductions from 11.8% to 18.3% for hydrocarbons, 33.0% to 45.3% for carbon monoxide and 14.7% to 18.1% for nitrogen oxides. Addendum #1 concludes that, while there are similarities between the Connecticut and Virginia programs, direct comparison of the specific "measure of emissions reduction" used in Virginia was not possible. This is primarily because, due to the shorter test time in Connecticut (35 seconds for all tests), failed vehicle average test results were not comparable with Virginia's test cycle (30 second preconditioning plus up to 90 seconds test time). Also, "initial pass" data indicated a possible difference in hydrocarbon analyzer calibration, although carbon monoxide and nitrogen oxide data were very similar by model year. In spite of the test cycle differences, a demonstration can be made that the Virginia program is more effective in reducing nitrogen oxide emissions than is the Connecticut program. Further work needs to be done to investigate the apparent hydrocarbon analyzer differences and to compare pollutant-specific fail rates.
Further information on this report can be obtained from Rich Olin at (804) 698-4425.