lations to reduce emissions substantially from light- and medium-duty vehicles beginning in model-year 1994. These regulations included stringent new exhaust emissions standards for nonmethane organic gas (NMOG), nitrogen oxides (NO_x), carbon monoxide (CO), particulate matter (PM), and formaldehyde.

Rather than requiring every vehicle to meet the same emission standard, the LEV program featured a fleet-based approach, which allows manufacturers the flexibility to meet new emissions standards averaged across their entire product line. This format of the standard, which reduces overall compliance costs, allowed manufacturers a longer development time for vehicles that are the most difficult to control. For LDVs, CARB defined a set of four categories of emissions standards and allowed each manufacturer to certify its vehicle models to any mix of the available standards, provided that the sales-weighted fleet of the manufacturer met the applicable average emission level for that model year. The four available emissions standards in order of increasing stringency were for the transitional low-emission vehicle (TLEV), low-emission vehicle (LEV), ultra-low-emission vehicle (ULEV), and zero-emission vehicle (ZEV). The fleet-average requirement was based on NMOG emissions, and this average became progressively more stringent each model year from 1994 through 2003 (see Table 6-1).

A second feature of the LEV program is that it sought to regulate the vehicle and its fuel as an integrated system. CARB determined that the proposed regulations would encourage vehicle and fuel manufactures to work together to develop LEVs and clean fuels (CARB 1990). In addition to California’s ultra-clean reformulated gasoline, the slate of clean fuels a manufacturer could choose from included methanol, ethanol, liquified petroleum gas (LPG), and compressed natural gas (CNG). Under the regulations, vehicle manufacturers were required to notify CARB 2 years in advance if they intended to certify a LEV vehicle using such an alternative fuel (13 California Code of Regulations [CCR] § 2303). If vehicle manufacturers announced an intention to market a combined total of at least 20,000 vehicles operating on a given clean fuel, then CARB would mandate the availability of such a fuel at California service stations (CARB 1990).

A third feature of the LEV program is that it included a mandate for ZEVs. CARB defined ZEVs as vehicles that have no exhaust or evaporative emissions of any regulated pollutant (CARB 1990). As initially adopted, this ZEV sales mandate required 2% of the passenger cars and light-duty trucks produced and delivered for sale in California by each