SULEV standards

The CNG vehicles were a technical success and included the first vehicles certified to the strict California low emissions vehicle (LEV) and ultra low emissions vehicle (ULEV) standards. They were also certified to the inherently low emissions vehicle (ILEV) category, and the full-sized van was certified to the California super ultra low emissions vehicle (SULEV) standard. 

Super ultra-low emission vehicle standard (SULEV), 10 57... 

The five categories of California Low-Emission Vehicle Program standards, from least to most stringent, are TLEV, LEV, ULEV, SULEV and ZEV. 

Even stiffer regulations apply to so-called Zero Emission Vehicles (ZEV), available to carmakers since 2003 for reduction of their average fleet emissions figures - also regulated by California law. ZEVs have to meet very tough exhaust standards ( SULEV ), in addition to which their HC emission from structural components ( nonfuel emissions ) must not exceed 0.35 g/test. Evaporative emissions from fuel and other liquid supplies ( fuel emissions ) are absolutely prohibited in these vehicles. 

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