Automakers must nearly double the average gas mileage for new cars and trucks by 2025 to meet regulations announced Tuesday by the Obama administration.

The fuel economy standard will climb year by year to 54.5 miles per gallon for the nation’s vehicle fleet, up from 28.6 mpg last year. The increase is intended to make deep cuts in the nation’s fuel consumption and greenhouse gas emissions.

Most automakers agreed to the new standards, and won some concessions, during a year of negotiations with environmental regulators. The rules are expected to step up development of electric and other alternative-fuel cars, and push more innovation to reduce fuel consumption in standard cars.

“We are giving manufacturers the regulatory certainty they need to deliver efficient cars that deliver what consumers want,” Transportation Secretary Ray LaHood said in a conference call with reporters.

“This may give Americans even more types of vehicles to choose from in the future.”

LaHood and Lisa Jackson, the Environmental Protection Agency administrator, said the average driver would save $8,000 in lower fuel costs over the life of a car bought in 2025, compared with one bought today. They said that benefit would outweigh the expense of better engines, lighter materials and other improvements needed to deliver better fuel economy – expected to increase the cost of a new car by an average $1,800.

“We know these standards are both achievable and cost-effective,” Jackson said.

The government previously set a standard of 35.5 mpg to be reached by 2016. The new standards for 2017 through 2025 represent the biggest steps the nation has ever taken to reduce carbon emissions and petroleum imports, the White House said.

The Natural Resources Defense Council predicted that North Carolina would cut its fuel consumption by 875 million gallons and its carbon pollution by 10.2 million metric tons each year, after the 2025 standard is in place.

“This is a monumental step forward in tackling global warming pollution and getting North Carolina off oil,” Elizabeth Ouzts, director of Environment North Carolina, a nonprofit advocacy group, said in a news release.

Former Massachusetts Gov. Mitt Romney, in Tampa on Tuesday to receive the Republican presidential nomination, has promised to roll back the Obama administration’s fuel-economy standards if he is elected. Romney’s campaign called the new rules extreme and said any fuel savings would be wiped out by the higher cost of new cars.

The chairman of the House Oversight and Government Reform Committee, Rep. Darrell Issa, R-Calif., said he supports the goal of higher fuel efficiency but thinks the new rules simply aim to appease the president’s environmental allies.

“The administration drafted these standards in secret, strong-arming automakers and short-circuiting the deliberative regulatory process to achieve a purely political result, abandoning sound science and objectivity to appease its political allies in the extreme environmentalist lobby,” Issa said.

In exchange for supporting the new standard, major automakers got California to promise that it would not adopt tougher new standards of its own. Manufacturers also will get credits for selling more natural gas and electric vehicles, and for using a different air-conditioning fluid that pollutes less.

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