Today's Washington Post confirms what I suspected, the new automotive fuel efficiency standards to be announced today will double as national vehicle emission standards for carbon dioxide (which only makes sense, as controlling fuel economy limits carbon dioxide emissions and vice-versa). It also explains why the automakers would accept the deal: "clarity and predictability," along with a single national standard It will also raise the average price of new cars by several hundred dollars, some portion of which will be offset by fuel cost savings.

Under the compromise, the federal government would establish two sets of standards, one for mileage and one for tailpipe emissions of carbon dioxide.

The Transportation Department's National Highway Traffic Safety Administration would set the new fuel-economy standards, which would raise the average fuel efficiency of a new car by 30 percent. Cars, for instance, would need to average 39 miles per gallon by 2016, while light trucks would need to reach 30 mpg.

The EPA, using its power to regulate carbon dioxide emissions under a 2007 Supreme Court ruling, plans a tailpipe emissions standard of 250 grams per mile for vehicles sold in 2016, roughly the equivalent of what would be emitted by vehicles meeting the mileage standard. Vehicles sold in 2009 are expected to emit about 380 grams per mile, industry sources said. The EPA needs to go through a rulemaking process to allow responses before the standards would go into effect.

One person involved in the negotiation said the Supreme Court's ruling on regulating emissions helped push companies to bargain because they feared the prospect of having to comply with separate EPA standards in addition to those from NHTSA and California.

"That's what brought the companies to the table," the person said.

The other thing the story notes is that the EPA will also go forward with standards for vehicle air coolant emissions, and that compliance with these rules may generate credits toward meeting the fuel economy standards.