In an historic move to boost fuel efficiency, the Obama administration proposed Wednesday to nearly double the required miles per gallon for passenger cars and light trucks by 2025.

The formal proposal follows President Obama's agreement with 13 major automakers, announced in July, to gradually boost these vehicles' fuel economy to the equivalent of 54.5 miles per gallon -- up from the current standard of 27.3 mpg. Last year, the administration finalized rules to hike the standard to 35.5 mpg by 2016.

""We expect this program will not only save consumers money, it will ensure automakers have the regulatory certainty they need to make key decisions that create jobs and invest in the future," U.S. Transportation Secretary Ray LaHood said in a joint announcement with the U.S. Environmental Protection Agency. He said they'll also reduce U.S. dependence on oil and protect the climate.

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The new CAFE (Corporate Average Fuel Economy) requirement for vehicles made between 2017 through 2025, which could be finalized next summer after a 60-day public comment period, is a combined city/highway rating. In real-world driving, as opposed to lab testing, the EPA has indicated that consumers should average about 39 mpg by 2025 -- up from about 22 mpg currently.

Environmentalists hailed what they said was their second major victory in a week, citing the Obama administration's surprise decision Thursday to reroute and thus delay until after the 2012 election the 1,700-mile Keystone XL oil pipeline from Alberta, Canada through six U.S. states to the Gulf Coast.

"These standards are just what consumers want and the country needs," said Frances Beinecke, president of the Natural Resources Defense Council. "By delaying a decision on the Keystone XL pipeline, and moving toward curbing carbon dioxide pollution from new power plants, the president's initiatives will help wean America from its oil addiction and begin to slow, stop and reverse climate change, and protect our health."

More than 100 members of Congress, including Rep. John Dingell, D-Mich., welcomed the tougher standards. In a letter Tuesday, they said the new requirements will "increase our national and economic security in an unprecedented way by dramatically decreasing our dependence on foreign sources of petroleum."

U.S. officials say cars, minivans, SUVs and pickup trucks account for nearly 60% of U.S. transportation-related petroleum use and greenhouse gas emissions.

Not everyone's on board. Rep. Darrell Issa, R-Calif, has criticized the new standards and more than 60 House Republicans said last month that they want to stop their finalization. They argued the new rules would hike vehicle prices.

"We are concerned that adding about $3,000 to the average cost of a car will price millions of Americans out of the market, which could reduce fleet turnover and delay environmental gains," the National Automobile Dealers Association said in a statement.

The Obama administration has estimated that new technologies for a 2025 vehicle will add about $2,200 in costs. However, it says lifetime fuel savings could average up to $6,600, leaving consumers with a net savings of about $4,400. The costlier technologies, mostly limited now to high-end vehicles, include turbocharging, direct fuel injection, electric drive and up to 10-speed automatic transmissions.

"No one really knows" how much extra a car meeting the 2025 standards will cost, says Jeremy Anwyl, CEO of Edmunds.com. He says the technology already exists but asks: "Can you build one at a price people are willing to pay and has all the features they want?"

Anwyl expects some manufacturers will ration the sale of larger vehicles by hiking their prices as a way to meet the overall standards.

The proposed 2017-2025 standard looks at carbon emission, set by EPA, and fuel economy, set by the DOT's National Highway Traffic Safety Administration. The requirements rise gradually during that period.

The EPA proposes that vehicles emit fewer than 163 grams of carbon dioxide per mile. Without any changes to the air conditioning refrigerant, a vehicle could meet that CO2 standard if it got 54.5 mpg by 2025. If the refrigerant were upgraded, it could do so at 49.6 mpg -- the official CAFE standard.

Federal officials say the tougher standards will rely on innovative technologies, some currently available such as advanced gasoline engines, vehicle weight reduction, lower tire rolling resistance, improvements in aerodynamics, diesel engines, more efficient accessories, and improvements in air conditioning systems.

They say the standards should also spur manufacturers to explore electric technologies such as hybrids and plug-in hybrids. Their proposal includes incentive programs to encourage early adoption of "game changing" advanced technologies, such as hybridization for pickup trucks.

The proposed rules say more than 80% of passenger vehicles meeting the 2025 standard will still have gasoline engines but many will be turbocharged. They say 15% will be hybrids and 3% will be powered by batteries.

They say nearly40 current models already meet the 2017 standards and some such --Toyota Prius, Ford Fusion hybrid, Chevy Volt, Nissan Leaf, Honda Civic hybrid and Hyundai Sonata hybrid -- even meet the 2025 standard.

"Our surveys show car buyers want better fuel standards, particularly because they want to spend less on gasoline. These standards put us on the right track toward the development of affordable, quality cars that use less gas," Shannon Baker-Branstetter, policy counsel for Consumers Union, said in a statement.

When asked if fuel economy standards should require auto manufacturers to increase the overall fleet average to 55 miles per gallon by 2025, she said 80% of respondents agreed.

Jonathan Browning, president and CEO of Volkswagen Group of America, said his company welcomes "a single, national fuel economy program." Yet he said the proposal is "not technology neutral" and does not encourage clean diesel, which is featured in its new mid-size Passat TDI.

After a public comment period, the DOT and EPA plan to hold several public hearings around the country.