In September of 1990 , in an effort to improve local air quality , the California Air Resources Board enacted the Low Emission Vehicle (LEV) program. The LEV program established several categories of emission standards for cars and light trucks. The most stringent of these categories was for the zero-emission vehicle (ZEV). The LEV program requires that , by 2003 , each of the seven largest automobile manufacturers (Chrysler,Ford , General Motors , Honda, Mazda , Nissan and Toyota) produce and offer for sale ZEVs at a rate equal to 10 % of the automobile sales each company has in the state , or about 110,000 cars per year. Similar mandates have also been adopted by New York and Massachusetts.

The impetus for the LEV legislation is the desire to reduce air pollution. In urban areas of Southern California, vehicles account for over 50% of the air pollution emitted. In 1995, the South Coast Basin (which includes Los Angeles, Orange, and parts of San Bernardino and Riverside counties) experienced 98 days in which the EPA health standard for ground - level ozone was exceeded . Ground - level ozone can cause aching lungs , wheezing , coughing and headaches . Serious health problems can also arise for those people with asthma , emphysema and chronic bronchitis . Children appear to be at particular risk. A 1984 study conducted at USC showed that children raised in the South Coast Basin suffered a 10% to 15% decrease in lung function. The deleterious effects of gasoline and diesel powered vehicles are not limited to air quality in southern California . In half of the world's cities , tailpipe emissions are the single largest source of air pollution. Worldwide, automobiles account for half of the oil consumed and a fifth of the greenhouse gases emitted. This situation is not expected to improve in the near future, as the number of cars and light trucks in the world – over 500 million – is expected to double in the next thirty years. Most of this growth will occur in developing countries which have little or no emission controls.