In the coming years, popular sport-utility vehicles, minivans, and other "light trucks" will have to clean up their act.
The Clinton administration is proposing the most far-reaching antismog regulations of the decade, aimed at an automobile culture spending more time on the road in gas-guzzling SUVs.
While the new regulations hearten environmentalists, the oil industry is still vowing to fight them. Automobile makers, expecting these changes, have been building trucks that meet California's cleaner standards for two years.
The new regulations to reformulate gasoline and reduce tailpipe pollutants may mean consumers will have to spend more for their next car - and the gasoline to drive it.
But the good news for environmentalists is that, even with the booming sales of SUVs, air quality will be preserved.
SUVs and other trucks will have to meet the same tough emissions standards that passenger cars do. And even those standards will be tightening, says EPA secretary Carol Browner.
Ordinary cars will be expected to cut their emissions of smog-causing chemicals almost in half, while SUVs, minivans, and pickup trucks - which have further to go to meet the new standard - will have to reduce their emissions by 95 percent over current levels.
A key component of the regulations, proposed by the EPA, is the removal of high levels of sulphur from gasoline. Sulphur levels will have to be cut 90 percent by 2006.
The oil industry resisted the change in their refining process, arguing that it would drive up the price of gasoline and force the closure of many small refineries.
In fact, Secretary Browner estimates low-sulfur gas will cost 1 to 2 cents more per gallon, or $12 to $24 dollars a year for the average family.
The new emissions controls may add $100 to $200 to the cost of new cars and trucks. "It's not an awful lot to pay for cleaner air," Browner says.
The regulations, expected to be adopted by the end of the year, were in reaction to falling air quality in several cities, Mr. Clinton said.
The wave of towering SUVs washing into suburban garages shoulders most of the blame.
While cars today run 95 percent cleaner than they did before emissions controls were introduced in the 1970s, they still account for one-third to half of urban smog, and as much as 22 percent nationwide.
Better pollution controls have brought air quality in line in most cities. But sales of light trucks, which burn more gasoline and have been subject to looser emissions standards, have equaled those of cleaner cars. And that shift has threatened the air-quality improvements.
The new standards don't address emissions of the greenhouse-gas carbon dioxide, however.
CO2, the same gas humans exhale, is a byproduct of burning fossil fuel. And the only way to make cars produce less of it is to make them burn less gas.
The most effective way to do that is to make automobiles smaller.
That's where the EPA's corporate average fuel economy (CAFE) regulations come in. All new cars sold by automakers in the US must average no less than 28.6 miles per gallon. So cars have shrunk and become more aerodynamic in the past quarter century.
That squeeze in passenger space has largely driven the move to trucks, which have to average only 20.4 miles per gallon.
EPA's new emissions regulation won't close that gap.
"We're not worried about tightening emissions regulations to the level of cars," said one Big Three executive who requested anonymity. "But if they abolish separate truck CAFE standards, we can't make it."
Many automakers, including Ford, Honda, and Toyota, already build trucks that meet the same emissions standards as automobiles under California's tougher regulations. Those standards are already tougher than the ones the EPA plans to replace.