Is It Safe to Drive SUVs?

Environmental Health Perspectives (December 1998)


The California Air Resources Board (CARB), often a bellwether of national regulatory trends, voted on November 5 to apply passenger car tailpipe emission standards to light trucks. The proposal to cut pollution from pickups, sport utility vehicles (SUVs), and minivans by the year 2007 is part of a broader effort to bring Southern California's air into compliance with the Clean Air Act.

The issue of light truck emissions is gaining importance because sales of such vehicles currently account for about 45% of total new vehicle sales. Between 1970 and 1995, the total miles driven by passenger cars grew 168%, while the mileage driven by two-axle, four-wheel trucks exploded by 558%, according to the American Automobile Manufacturers Association report AAMA Motor Vehicle Facts and Figures, 1997. Although light trucks, particularly SUVs and minivans, are increasingly used as passenger vehicles, they can create far more pollution than cars.

Federal pollution and fuel efficiency regulations are significantly looser for light trucks (with loaded vehicle weights above 3,750 pounds) than passenger cars. In California, light trucks with loaded vehicle weights between 3,750 and 5,750 pounds can emit 33% more nonmethane hydrocarbons (an ozone precursor) than passenger cars, 100% more nitrogen oxides (NOx), and 30% more carbon monoxide (CO). EPA figures show that motor vehicles overall account for 35% of NOx, 64% of the national output of CO, and 27% of volatile organic compounds.

The auto industry opposes further regulation, saying trucks pollute more than cars because they're heavier and designed for hauling. "The higher standard is a reflection of the fact that they do more work," says Sam Leonard, director of mobile emissions and fuel economy at General Motors. "The controls we have are virtually identical to what's on passenger cars. It's not that we've scrimped on cost or hardware or engineering to make them as clean as possible."

Leonard also says most of the benefits of tightening emissions standards have already been realized. Today's cars and trucks, he says, are 97 - 99% cleaner than models sold during the 1960s, and each further increment of cleanup will incur ever greater cost.

Environmentalists see matters differently. Roland Hwang, a transportation analyst with the Union of Concerned Scientists, says the 97% claim is "exaggerated, and not relevant to whether cars are still a problem." Hwang says in the real world cars and trucks pollute much more than under laboratory conditions due to aggressive driving, poor maintenance, and the fact that pollution measurements are made with air conditioners shut off. Hwang also says the share of smog-forming pollutants (hydrocarbons and NOx) attributable to light trucks more than doubled between 1965 and 1995, making them a target ripe for control.

And while auto manufacturers complain they'll have trouble meeting the tighter standards, California's air regulators assert that they have conducted tests in which they changed the nature and location of the catalytic converter on a heavy SUV and "met the standard we're proposing," says Richard Varenchik, an information officer for the CARB.

As often happens, California's light truck rule foreruns a national effort to regulate the environmental effects of the increasingly popular vehicles. A draft of the EPA's Tier II auto pollution regulations is due in December 1998, with a regulation due one year later. How the regulation will treat light trucks is still uncertain.

Both the EPA and CARB are focused on emissions, not fuel efficiency, where light trucks again enjoy a significant regulatory advantage. While the Corporate Average Fuel Economy (CAFE) system requires each manufacturer's fleet of cars to average 27.5 miles per gallon, light trucks must average only 20.7 miles per gallon. Yet with the rising popularity of the heaviest SUVs, all three U.S. automakers failed to meet that standard for the 1997 model year. (Because several years' averages can be lumped together, one year's average does not violate the Clean Air Act.)

To Leonard, that difficulty is a good indication of the futility of tighter mileage requirements. "Judging by the difficulty that we and other domestic manufacturers of full lines of trucks and SUVs have had in meeting CAFE, there's very little ability to improve at a reasonable price," he says. But environmentalists argue that 6,000-pound vehicles with V-8 engines are not necessary to haul groceries from the supermarket. "All the improvements [in fuel economy] are getting eaten by increases in performance [such as more horsepower, bigger engines, and faster driving speeds] and rising vehicle weight," says Martin Thomas of the American Council for an Energy Efficient Economy in Washington, DC. "If we held performance constant, there could be improvements in fuel economy."

SUVs also have an outsized appetite for other raw materials. The auto industry already consumes 27% of aluminum, 35% of iron, and 14.5% of steel used in the United States. As increasing sales of ever larger trucks boost the average vehicle size, rising materials consumption will raise the environmental toll of mining, processing, and discarding or recycling these materials.

The issue of size also plays a role in safety. SUVs and light pickups are not only more massive than cars, they also have high, stiff frames that override the protective component of cars. When one car strikes another, 6 people die in the struck vehicle for every 1 in the striking vehicle, according to Julie Rochman, communications director of the Insurance Institute for Highway Safety, an industry group in Arlington, Virginia. But when SUVs strike cars, the ratio is 27 to 1.

That doesn't mean that SUVs are any safer than cars, however. Rochman points out that since SUVs have high centers of gravity, they roll over easily. Indeed, the institute recently analyzed car and truck accidents and, Rochman says, found that "in each weight class, if a crash takes place, your chances of survival are better in a car."

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