double the efficiency burn less fuel double the efficiency standards 54.5 mpg regulate emissions of greenhouse gases 54.5 mpg by 2025 tough new mileage standards August 2012 new fuel economy standards August 2012 mileage-and-emissions announced in 2012 finalized in 2012 claims The Washington Post. according to average 54.5 miles per gallon mileage-and-emissions according to announced