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Heavy-duty vehicles account for approximately 30 percent of the oxides of nitrogen (NOx) and 65 percent of the particulate matter (PM) emissions from the entire California on-road fleet, despite the fact that these vehicles comprise only 2 percent of the same. To meet legislative mandates to reduce excess smoke emissions from in-use heavy-duty diesel-powered vehicles, the Air Resources Board (ARB or Board) adopted, in December 1997, amendments to the regulations governing the operation and enforcement of the Heavy-Duty Vehicle Inspection Program (HDVIP or the “roadside” program) and the Periodic Smoke Inspection Program (PSIP or the “fleet” program). The initial roadside program was adopted in November 1990 in response to Senate Bill (SB) 1997 (stat. 1988, ch. 1544, Presley), and enforced from 1991 to 1993. It was suspended in October 1993, when the Board redirected staff to investigate reformulated fuels issues.

This paper presents the results of a study which examined short test results and repair data on 1980 (GM vehicles only) and 1981 (all makes) model year passenger cars participating in the Arizona Inspection and Maintenance (I/M) program. The primary purpose of the study was to gather information on the failure rates of these vehicles using the Arizona short test, their mean emission levels, and the types of repairs performed on the failing cars. A unique part of the study was that a generalized software system was developed to extract very specific emission control information from the vehicle identification numbers (VIN's) for these vehicles. The results of the study indicate that in general these vehicles have quite low failure rates in comparison with pre-1980 vehicles, and that certain vehicles have a higher probability of failing the short test than others.