Q. What will the rules do, exactly?

A. They’ll restrict the greenhouse gas emissions from cars and trucks — essentially forcing them to get better fuel economy. By 2016, vehicles sold in the United States will average 35.5 miles per gallon, up from 25 mpg today. The White House estimates the new regulations will save a total of nearly 2 billion barrels of oil from 2011 to 2016 and, in global warming terms, represent the equivalent of taking 177 million cars off the road.

Q. Do I have to trade in my Yukon for a Prius?

A. No. The new regulations would apply only to new cars. You don’t have to scrap your gas guzzler, and you won’t need to retrofit it.

Q. Will this change my car-buying choices?

A. Yes. For one thing, the Obama administration projects you’ll pay an extra $600 per vehicle, on average, in 2016 because of the new rules. It’s also likely that U.S. dealerships will stock more light vehicles with less trunk space, and very possibly more advanced-fuel vehicles such as plug-in hybrids.

Q. The federal government right now has such a heavy hand in running two big U.S. automakers due to their need for federal aid. Is that why the auto companies agreed to this?

A. It’s one of several factors that appear to be at play, including California’s push to set tough vehicle emissions standards and the Environmental Protection Agency’s decision, spurred by a Supreme Court ruling, to propose regulating greenhouse gases under the Clean Air Act — all of which have pressed automakers to compromise on a national fuel standard.

(c) 2009, Tribune Co. Source: McClatchy-Tribune Information Services.