NEW YORK – California regulators have realized that manufacturers won't be able to make as many hydrogen-fueled cars by 2014 as regulators had once hoped, according to Forbes. The California Air Resources Board voted unanimously during the last week of March to scale back the ambitious automotive clean air rules it adopted five years ago. The board ruled that the six largest automakers operating in the state will collectively need to produce 7,500 zero-emissions vehicles by 2014 — 70 percent fewer than the 25,000 ZEVs it had mandated in 2003.

This is the fourth revision of California's clean air standards since the state instituted its first zero-emissions vehicle mandate in 1990.

The new ruling relieves pressure on automakers such as General Motors and Toyota, which have focused much of their clean vehicle programs on cars that rely on batteries to reduce fuel consumption and emissions.

Under the latest revision, the automakers will be able to substitute 58,000 plug-in hybrids to compensate for the reduction in zero-emissions vehicles. GM is designing its Volt plug-in electric, a car designed to run for 40 miles between charges on batteries, for 2010 introduction.

Toyota has sold 1.2 million hybrids like its Prius since 1997 and plans to roll out a limited number of plug-in versions of its hybrid to fleet users within two years.

As a result, only about four percent of the cars sold in California in 2014 will need to have zero-emissions designs.

GM has already sent 40 Equinoxes onto California roads, providing the cars to customers in two zip codes in Southern California with requisite hydrogen stations. As part of the California ruling, the Air Resources Board has 15 days to come up with initial suggestions for how to create a more extensive refueling infrastructure.

Despite reducing the number of ZEVs, the new rules will result in cleaner air. There will be a 7,000-ton reduction in smog-forming emissions, and 5,500 fewer tons of carbon dioxide emissions between 2012 and 2017, thanks to a greater number of greener vehicles, according to Forbes. And, automakers estimate that the clean technologies will cost them a collective $1 billion per year between 2012 and 2014, when the clean vehicles will go into production.

GM, Ford, Chrysler, Toyota, Honda, and Nissan will need to produce 58,000 plug-in hybrids and 7,500 zero-emissions vehicles, which can be powered either by batteries or hydrogen fuel cells. (Car makers selling fewer than 60,000 cars a year in California, which currently includes Mercedes, BMW, and VW, are exempt.)