Less than a year after everyone with any sort of say in the matter seemed to agree that 54.5 miles per gallon by the year 2025 was a properly attainable goal, the California Air Resources Board has decided to change things up a bit.

In addition to CAFE requirements of a 54.5-mpg fleet average (using the government's formula, not what you see on window stickers), at least 15.4 percent of all cars sold by any major automaker doing business in California will have to be either fully electric, a plug-in hybrid or be powered by a hydrogen fuel cell by 2025. There are questions about the "over-compliance" section of the bill, which we'll be investigating further.

According to Mary Nichols, chair of the California Air Resources Board, 15.4 percent is "actually a relatively modest goal, but that's all that we're mandating." Most automakers are on board, says Nichols. "Probably the most heartening aspect of this whole rulemaking was the level of cooperation that we received from the industry... Overall, the degree of support for the package was just extraordinary."

Even if automakers are on board, though, there's still a question of who will actually buy the vehicles. While everyone wants better fuel efficiency, not everyone is willing to pay for it, counters the California New Car Dealers Association, estimating that the plan would add about $3,200 to the average price of a new car or truck. Perhaps to help dissuade such fears, Nichols added that "direct incentives to people who buy these cars (like) rebates and credits" are also in the works.

At least 10 more states are likely to follow California's lead, reports Automotive News. That would put the total number of advanced green vehicles (either with a plug or powered by hydrogen) at around three million total units by 2025, 1.4 million of which would be in California.