The rules derive from the Environmental Protection Agency's regulation of pollution. The 1970 Clean Air Act was intended to cut pollution from cars, factories and other sources. A Supreme Court decision since has categorized carbon emissions, which are blamed for global warming, as a pollutant, requiring the EPA to regulate them.
The carbon dioxide that comes out of a car's exhaust is directly linked to the amount of fuel it burns, so the new regs set 163 grams of carbon emissions per mile as the target, and that converts to 54.5 mpg.
The 1975 Energy Policy Conservation Act, passed in reaction to U.S. gasoline shortages during the 1973 Arab oil embargo, meanwhile set the first miles per gallon rule and aimed to double fuel economy at the time. The latest standards now also are touted as enforcing a doubling of mileage.
Bob King, president of the United Auto Workers union, also applauded the rule, saying, "These new standards will help propel the auto industry forward by giving American families long-term relief from volatile fuel prices. Lowering the total cost of driving will make automobiles more affordable and expand the market for new vehicles."
NADA said the opposite, that higher prices would slice 7 million buyers from the new car market.
USA TODAY poll results have indicated that high fuel prices alone aren't enough to get Americans to shift to more fuel-efficient ways.
A poll taken mid-March 2011 — when regular-grade gasoline averaged $3.97 across the U.S., near that year's peak of $3.99 and higher than the current average of about $3.76 — found just 32% of Americans saying that they'd switch to a more fuel-efficient car if gas hit $5. (The record national average to date is $4.11, set in July 2008.)
Another 13% said they wouldn't make the move unless fuel was $6 to $7.99. And a surprising 38% said they wouldn't trade for gas-sippers no matter how high fuel prices rose.
Even so, LaHood insisted on Tuesday that such fuel-stingy cars are "wildly popular."
Your mileage may vary
One thing that is not debated, however: You won't see 54.5 mpg on the window stickers of those 2025-model cars and trucks.
That's because the CAFE standards are set using laboratory tests for combined city and highway driving.
But the EPA window-sticker mileage rating is calculated from those results using a formula that tries to make the sticker number match likely real-world results — about 20% lower than lab results.
Automakers also can earn credits in other ways toward their 54.5 mpg requirement.
The goal is first reduced by as much as 5 mpg for automakers who can maximize credits for using more-efficient air conditioning but also for using more environmentally benign air conditioning coolant, Hwang says.
So the actual CAFE mpg number thus could be down to 49.5 mpg or so, and the window-sticker adjustment formula would slice that further to a window-sticker rating for combined city/highway driving of 39 or 40 mpg.
Some hybrids already meet that, and diesels come close. Many more gasoline cars are in the low- to mid-30s. And the handful of electric cars on the market have mpg-equivalent ratings of twice the new CAFE standard.