U.S. EPA and the Department of Transportation’s National Highway Safety Administration (NHTSA) have proposed a National Program intended to reduce greenhouse gas emissions and improve fuel economy for new cars and trucks sold in the United States. Applicable to model years 2012 through 2016, the new standards would require an estimated average emissions level of 250 grams of carbon dioxide per mile (equivalent to 35.5 miles per gallon) and, if successful, would reduce carbon dioxide emissions by an estimated 950 million metric tons over the lifetime of the vehicles sold.
More on the program can be found here.