FEATURE ARTICLE
Safer Vehicles for People and the Planet
Motor vehicles contribute to climate change and petroleum dependence. Improving their fuel economy by making them lighter need not compromise safety
Thomas P. Wenzel, Marc Ross
What Then Must We Do?
For too long the conventional wisdom that lighter cars and trucks are less safe has helped stymie efforts to increase the fuel economy of new vehicles and to reduce their greenhouse-gas emissions. This is a shame. One reason is that automotive engineers can improve fuel economy with no or little reduction in vehicle mass. Another is that with thoughtful design, lighter and smaller models can be made just as safe as larger, heavier ones, allowing even greater fuel economy.
The NHTSA recently issued rules modestly tightening fuel-economy standards for light-duty trucks, increasing the requirement for this category (which includes SUVs and minivans) from 22.2 miles per gallon to 23.5 miles per gallon by 2010. But the U.S. Court of Appeals overturned that measure in November 2007, telling the NHTSA, in essence, to do better. The scheme that the judges shot down continued to allow trucks to have lower fuel economy than cars; the NHTSA proposal also allowed larger trucks (defined by their "footprint") to have poorer fuel economy than smaller trucks. This size-based standard is preferable to a weight-based one that some were proposing, but it is still lacking, for many reasons.
The NHTSA adopted a size-based standard for trucks because regulators are clinging to the myth that smaller trucks are intrinsically less safe than larger ones. We and others have shown that this belief is unfounded: The center of gravity (in rollovers) and frontal height and stiffness (in crashes with objects), not footprint, are the important variables controlling protection of a vehicle's occupants. What's more, our analysis shows that larger pickups (as measured by their rated capacity) impose greater risk on the occupants of other vehicles than do smaller pickups.
So the NHTSA's size-based standard is not necessary to protect truck drivers. Worse, it jeopardizes car drivers. And the size-based standard fails to set any overall requirement for a manufacturer's fleet of light trucks. So by shifting production toward larger models, an automaker could in effect relax the fuel-economy requirements under which it currently operates. Clearly, such toothless measures will not provide the dramatic reductions in carbon dioxide emissions needed to combat global warming, nor will they put a dent into the problem of excessive dependence on foreign oil.
As the agency responsible for regulating both fuel economy and safety, the NHTSA can and should do better. It should not try to regulate safety through the back door, by manipulating fuel-economy standards in such a way as to promote the sale of vehicles that some people believe might be less dangerous to their drivers by virtue of their great size and weight. Rather, the NHTSA should set fuel-economy standards independently from safety standards. For the latter, the nation clearly needs rules that take into account not just the dangers to a vehicle's occupants, but also the risk that a car or truck poses to others on the road.
The 2008 energy bill the President recently signed requires that new cars and light trucks have an average fuel economy of 35 miles per gallon by 2020. Although this legislation does not explicitly call for a size-based standard, it still allows separate fuel-economy levels for cars and trucks. By continuing to treat cars and light trucks differently, the provisions of the new law, as well as current safety standards, encourage consumers to purchase gas-guzzling and aggressive pickups and SUVs. Steps should be taken to apply the same standards equally to all light vehicles.
Requiring that all light-duty vehicles meet the same stringent fuel-economy standards would increase the manufacturing costs of large pickup trucks and SUVs substantially. But some sticker shock here would be beneficial, because it would discourage consumers from purchasing a big vehicle unless they really needed one. Those people who truly require a large truck, say to pull a trailer or to haul cargo for a business, could be helped by offering them appropriate tax incentives (as are available now for vehicles weighing more than 6,000 pounds). So large pickup trucks and enormous SUVs would still be around, but over time they would presumably be found in dwindling numbers.
That change alone would improve highway safety for society as a whole. Other gains would come from appropriate regulations on vehicle compatibility and aggressivity, tougher roof-crush standards and improved seat-belt technology, which together would save far more lives than might possibly be put in jeopardy by tightened fuel-economy standards. There's really no reason to think that you can't save people and the planet at the same time.
Bibliography
- Ross, M., D. Patel and T. Wenzel. 2006. Vehicle design and the physics of traffic safety. Physics Today 59:49-54.
- Wenzel, T. P., and M. Ross. 2005. The effects of vehicle model and driver behavior on risk. Accident Analysis and Prevention 37:479-494.
- Latin, H., and B. Kasolas. 2002. Bad designs, lethal profits: The duty to protect other motorists against SUV collision risks. Boston University Law Review 82:1161-1223.
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