In the 40-year history of the Act, EPA has granted approximately 50 waivers to California for innovations like catalytic converters, exhaust emission standards, and leaded gasoline regulations. Until last month, a waiver request had never been denied. According to the governor’s website, the ARB-adopted regulations will ramp up over eight years to cut global warming emissions from new vehicles by nearly 30 percent by model year 2016 -- the equivalent of taking 6.5 million cars off the road by the year 2020. If the 14 other states with similar plans follow through, that figure would grow to more than 22 million vehicles and would cut gasoline consumption by an estimated 11 billion or more gallons a year.

The California Air Resources Board says that the California rules would be significantly more effective at reducing Greenhouse Gas emissions than the federal program, and they also yield a better fuel efficiency – roughly 44 mpg in 2020 for the California vehicle fleet as compared to the new Federal standard of 35 mpg. The auto industry is maintaining that the regulation of greenhouse gas emissions is simply another method of regulating fuel economy, and, therefore, that California’s emissions standards (and identical standards adopted by other states) are preempted Federal law. Due to the precedent set by past approval of waivers by the EPA, and reports indicating that the California standards are more effective than EPA standards, supporters of the California emission standard say the EPA’s decision to disallow the waiver is based on political reasons.