Questions and answers about gas mileage standards

DETROIT — The Obama administration finalized regulations on recently that would make auto companies nearly double the average gas mileage of all the new cars and trucks they sell by 2025. All new vehicles would have to average 54.5 miles per gallon in 13 years under the new standards.

The requirements will be phased in gradually between now and 2025. Here are some questions and answers about the new rules:

Q: Where did the 54.5 mpg figure come from?

A: It came from the Obama administration’s wish to cut vehicle carbon dioxide emissions in half and reduce dependence on foreign oil. Carbon dioxide is the primary greenhouse gas caused by human activity, and scientists say it is leading to potentially dangerous changes in the climate. The 54.5 mpg target is roughly what it would take to cut the emissions.

Q: Does this mean each new car or truck will get 54.5 miles per gallon in 2025?

A: No. It’s an average required of all vehicles sold in 2025. The number also isn’t a real-world figure. It’s a government target that requires each automaker to build cars that burn through less gasoline and introduce technology that lowers other kinds of pollution. The standards will be reviewed in 2018 and could be changed.

Q: So what’s the real-world average?

A: The average new car will get 45 miles per gallon, and the average truck will get 32 mpg. The nation’s fleet of new vehicles will get about 40 mpg in 2025.

Q: Why the difference?

A: It’s complicated, but it’s because people in the government who came up with the gas mileage standards calculate fuel economy differently from the people who figure out the gas mileage number on car window stickers. The window-sticker numbers are closer to reality.

Q: How else do you raise fuel economy except by selling more fuel-efficient vehicles?

A: Automakers also can lower their mileage targets with credits for cutting pollution. For example, using air conditioning refrigerant that doesn’t pollute as much as current fluids in cars and trucks.

Q: Will automakers have to sell different kinds of cars and trucks to meet the new requirements?

A: Yes, but it will take some time. Drivers will see changes in the kinds of vehicles sold as carmakers try to boost their numbers. There will be more small cars and more hybrids, natural gas vehicles, plug-in hybrids and all-electric cars. The government and the nonprofit Center for Automotive Research both estimate that hybrids and electrics will make up 10 percent of vehicles available in 2025, up from 3 percent now. There could also be more diesels or even cars that run on hydrogen. Requirements for pickup trucks won’t be as stringent as cars at first, giving automakers time to develop technology for the trucks. Hybrids and electric cars are already well on their way to meeting the standards — and even exceeding them.

Q: What are examples of existing models that get high mileage?

A: The all-electric Honda Fit gets the equivalent of 118 mpg, which is calculated based on the energy it uses. Its rival, the electric Nissan Leaf, gets 99 mpg. Ford’s new C-Max hybrid will get 47 miles per gallon when it goes on sale this fall.

Q: What technology will help boost fuel economy over the next decade?

A: The government says most of the changes will be new technology added to gasoline engines. So you’ll see more gas-saving devices such as stop-start systems, which temporarily shut off engines at stop lights. Carmakers will use more efficient transmissions, smaller but more powerful turbocharged engines and engine technology like direct fuel injection, which saves gas. They’ll also try to make vehicles lighter using aluminum and other lightweight materials.

Q: How much will the new regulations add to the price of a car?

A: The government says vehicles will cost an average of $2,800 more than they do today, based on the value of a dollar in 2010. Critics, like Mitt Romney and the National Automobile Dealers Association, say the increase could make cars unaffordable for many. But the government says the fuel cost savings will more than offset the added cost of cars and trucks. The government expects consumers to save $5,700 to $7,400 on gasoline during the lives of their cars. That’s based on an average gas price of $3.87 per gallon.