The government announced tough new fuel-economy standards in a proposed rule that also would place the first nationwide limits on vehicles’ greenhouse gas emissions, blamed for global warming, according to USA Today.

The Obama administration outlined its targets in May, but final details were uncertain until the joint announcement by the federal Department of Transportation and Environmental Protection Agency.

The rules would phase in with 2012 models, when the current rules end, and escalate so that by the 2016 model year, the industry would have to average the equivalent of 35.5 miles per gallon.

The administration estimates the rules would add an average of $1,100 to the price of a car but could save $3,000 on fuel over the vehicle’s life.

New rules were required by Congress in the Energy Act of 2007. The proposal will be open to public comment for 60 days before it can become final.

The current rules call for 2009-model cars to average 27.5 mpg and trucks, 23.1 mpg. But the National Highway Traffic Safety Administration reported in March that today’s new cars actually average 32.6 mpg and trucks, 24.2.

To hit the 2016 targets, automakers plan to field more small cars and smaller engines with advanced technology. Ford Motor plans to bring an array of its small, European-market cars. Fiat-controlled Chrysler will sell versions of the Italian maker’s small cars. General Motors Co. plans to boost its offerings rated 30 mpg or more on the highway by 65%.

The proposed rules are partly a compromise to head off a patchwork of state rules. California, since joined by 13 other states and the District of Columbia, tried to impose its own greenhouse gas (ghg) limits, which are directly tied to fuel economy. “The administration proposal is identical to California’s,” said Mary Nichols, head of the state’s Air Resources Board. She applauds that for the first time both better mileage and ghg limits are required. Says Jim Kliesch, senior engineer at the Union of Concerned Scientists, “You have to go back to the days of disco to see a fuel-economy improvement like this.”

Details, quirks and loopholes in the proposal:

  • If an automaker exceeds its target, it can bank the extra mileage as credit against future shortfalls.
  • The industry goal is 35.5 mpg, but targets will vary by company, based on its mix of vehicles. A small-car specialist would have a higher target than a company with a wider range of vehicles.
  • Because the rules include emissions, the overall standard isn’t strictly 35.5 mpg and could be as low as 34.1 mpg. Automakers would get credits for cutting ghg emissions in other ways besides burning less fuel, such as preventing air conditioning leaks. The coolant is 300 times worse on the ghg scale than carbon dioxide, the engine ghg.