The U.S. government has already voted in favour of forcing carmakers to lift their fleet average fuel consumption figure to 35mpg by 2020 but what the feds didn’t outline was what interim fuel economy targets will come into effect in the meantime. This uncertainly forced a number of carmakers to put development plans for several new models on hold, most notably GM and its RWD sedan and sports car program.

The National Highway Traffic Safety Administration (NHTSA) has now submitted its proposal for annual fuel economy increases to the White House, a document which proposes four years of fuel economy increases with the first starting in 2011. According to The Detroit News, the NHTSA proposal also includes a credit-trading system for carmakers where firms exceeding the standards could sell credits to other firms that can’t meet the deadlines.

Although the government claims the new legislation will help address the issue of soaring energy costs, there are many who believe the higher CAFE standards will add several thousand dollars to the price of every vehicle, including GM exec Bob Lutz who earlier stated it could add up to $6,000 to the cost of a new car.