Ultra-low-emission vehicle

An ultra-low-emission vehicle (ULEV) is a motor vehicle that emits extremely low levels of motor vehicle emissions compared to other vehicles. In some jurisdictions it is defined in law; low and ultra low emission vehicles may be given tax or other advantages, while high emission vehicles may suffer restrictions or additional taxation.
In California.
California defines a ULEV as a vehicle that has been verified by the California Air Resources Board (CARB), United States to emit 50% less polluting emissions than the average for new cars released in that model year. 
Under LEV II regulations, the Tier I and TLEV classifications were removed for 2004. The ULEV is one of a number of designations given by the CARB to signify the level of emissions that car-buyers can expect their new vehicle to produce and forms part of a whole range of designations, listed here in order of decreasing emissions: