Topic Area: Transportation

Geographic Area: United States

Focal Question: How effective has California’s Vehicle Emissions Programs been in increasing the number of green vehicles available for sale in California and the U.S.?


(1)  “Advanced Search Results | Green Vehicle Guide | US EPA.”  Environmental Protection Agency.  Accessed: 04/05/2008.  <>.

(2)  Brown, Mark B.  “The Civic Shaping of Technology: California's Electric Vehicle Program.”  Science, Technology, & Human Values, Vol. 26, No. 1 (Winter, 2001), pp. 56-81.  Accessed: 04/06/2008.  <>.

(3)   “Fact Sheet: LEV II – Amendments to California’s Low-Emission Vehicle regulations.”  California Air Resources Board.  Feb. 1999.  Accessed: 04/05/2008.  <>.

(4)  “Fact Sheet: The Zero Emission Vehicle Program.”  California Air Resources Board.  Mar. 28, 2008.  Accessed: 04/06/2008.  <>.

(5)  Sullivan, Colin.  "California: State Agency Discards Old 'ZEV' Program Again."  ClimateWire.  E&E Publishing, LLC.  3/28/2008.  <>

Reviewer: Adam L. Rich, Colby College ‘08


In 1990, the state of California implemented vehicle emissions restrictions known as the Low-Emission Vehicle program.  This plan included two sections: a low-emission vehicle standard (LEV), and a zero-emission vehicle standard and quota (ZEV) designed to stimulate the creation of newer technologies (CARB LEV-II Fact Sheet; CARB ZEV Fact Sheet).  These emissions programs have had both positive and negative impacts on the availability and manufacturing of environmentally friendly vehicles.

In 1998, the California Air Resources Board revised their original Low Emission Vehicle program to expand and enhance their restrictions on vehicle emissions, known as LEV-II.  In this revision, they expanded the program to cover all SUVs and trucks, as well as reducing the level of allowable NOX emissions and raising the standards for average fleet emissions.  However, from this revision came the creation of a significant new category of low emissions vehicles: Super-Ultra Low Emissions Vehicle (SULEV).  According to CARB, a SULEV compliant vehicle would “emit only a single pound of hydrocarbons during 100,000 miles of driving” (CARB LEV-II Fact Sheet).  To encourage the creation of these vehicles, CARB allowed standard gasoline powered SULEVs to count as 0.2 ZEV credits (CARB LEV-II Fact Sheet).

This new emissions standard had a significant effect on the number of green vehicles produced by automobile manufacturers.  From model year 2003, the year before the LEV-II standards were to take effect, to model year 2008, the number of available SULEV compliant vehicles for sale increased dramatically.  According to the United States Environmental Protection Agency, in MY2003, only six SULEV compliant vehicles were available for sale in the United States (specifically California and the northeast).*  By MY2005, one year into the program, some 21 SULEV compliant vehicles were available within the United States.  According to the most recently available data, MY2008, 36 SULEV compliant vehicles are available for sale within the United States, a six-fold increase since 2003 (CARB LEV-II Fact Sheet; EPA).

The other part of California’s vehicle emissions regulation program was the enactment of a program to mandate the sale of zero emissions vehicles (ZEV) within the state.  The implementation of this program sought to force technology capable of reducing greenhouse gasses in the state (Brown; CARB ZEV Fact Sheet). 

Initially, in 1990, the program required that 10% of all vehicles sold in the state of California have zero emissions by the year 2003.  This was designed to effectively force the development of emissions reducing technologies.  A $5000 fine was to be assessed on every car under the quota, providing significant incentive to develop newer technologies (Brown; CARB ZEV Fact Sheet).

However, gradually over time, the state has significantly eased their requirements for pure zero emissions vehicles.  In 1996, the state allowed for partial-zero emissions vehicles (PZEV) to count as partial credit towards automobile companies’ ZEV quota.  In 2001, CARB significantly reduced the required quota of pure zero emissions vehicles by breaking down the ZEV requirements into subcategories, requiring that 6% overall be PZEV, 2% overall be advanced technology (AT) PZEV, and only 2% be ZEV.  In 2008, CARB further reduced that quota by creating a fourth category, Enhanced AT-PZEV.  While they increased the overall quota to 12%, the total percentage of pure zero emissions vehicles that must be sold in the state can be as little as 0.9% annually (CARB ZEV Fact Sheet).

According to their own figures, the current number of pure zero emissions vehicles currently on the road in the state of California is equivalent to 3.8% of all ZEV/PZEV vehicles, significantly below the original 10% of overall sales, and still well below the 2001 revised mandate of 20% of all ZEV/PZEV vehicles.  With their new updated regulations, automakers are required to make 70% fewer pure zero emissions vehicles during the period of 2012 to 2014 than they would have previously.  They would be able to replace them with easier to make Enhanced AT-PZEVs such as plug-in hybrids.  While the current iteration of the ZEV program does promote the creation of newer and cleaner vehicles, it hinders its original goal by diminishing the importance of the zero emissions vehicle (CARB ZEV Fact Sheet; ClimateWire).

*The EPA’s Green Vehicle Guide distinguishes different vehicle models by different combinations of body style, engine, and transmission.  For the purpose of this summary, different vehicle models sold under the same name have been combined and counted as a single model.