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Reading Safety Gauges
Reading Safety Gauges
Evans Op-Ed in The Washington Times
March 02, 2002
The federal government's vehicle fuel economy program has been around for more than a quarter-century, but it is more hotly debated today than ever before. Congress is considering whether to significantly tighten the federal miles-per-gallon standards known as CAFE (for Corporate Average Fuel Economy). Those advocating such a change claim to find support in a long-awaited report released last summer by a committee of the National Academy of Sciences.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
But the report contained a far more important finding about CAFE - namely, that it has proven deadly in the past because it forced us into lighter cars, leading to an additional 1,300-2,600 traffic deaths per year.
Having devoted a career to scientific research into traffic safety, and having written numerous technical papers on the issue of vehicle weight and safety, I can assure you that the finding that CAFE is lethal rests on rock-solid evidence. It has been neglected in the past, but it demands our attention now.
Traveling in a larger, heavier vehicle reduces your risk of being killed in a crash. There is no more firmly established conclusion in the vast body of traffic safety research. The evidence supporting this is more extensive and clearer than the evidence showing that driving faster, or while drunk, increases your risk of being killed. These are solidly established effects that no serious traffic safety researcher disputes.
Yet even though the evidence is even stronger that smaller, lighter vehicles increase risk, that risk is ignored by advocates of higher CAFE standards. They claim, for example, that if everyone drove a smaller vehicle, we could have higher fuel economy without increasing fatalities. This is false. For two-vehicle crashes, it is true that making one vehicle lighter reduces the risks to the occupants of the other vehicle. But the central fact is that about half of all occupant deaths occur in single-vehicle crashes. In such a crash, if my vehicle is smaller, my risk of being killed increases; the size of other vehicles is irrelevant.
CAFE forces us to buy vehicles that are smaller than we would otherwise chose. This increases single-vehicle fatality risk in two ways. First, for similar types of vehicles, the smaller the vehicle, the more likely it is to overturn. Rollover crashes account for about 40 percent of single-vehicle crash deaths.
Second, the lighter my vehicle, the less it will damage or move any object it strikes. The most commonly struck object causing death is a tree. A heavier vehicle is more likely to uproot a tree and continue moving forward. This dramatically reduces occupant risk compared to a lighter vehicle being stopped on impact. And if I happen to hit a brick wall, a heavier vehicle will penetrate further into it than a lighter vehicle, similarly reducing my risk.
The two-vehicle crash case is more complicated. If my neighbor transfers to a lighter vehicle, his or her risk goes up, but my risk goes down. Beyond troublesome ethical questions lies a complicated technical problem: Does my neighbor's risk go up more than mine goes down? The answer depends on the size of the neighbor's new and former car, and on the size of my car. For most combinations, our net risk goes up. For example, if two 2,000-pound cars crash into each other, driver risk is about 50 percent higher than if the cars weigh 3,000 pounds each.
In short, heavier cars are clearly safer in single-car crashes.
Multiple-vehicle crashes are more complex, but heavier is still likely to be safer. When all crashes are considered, heavier is certainly safer. If higher CAFE standards force us into lighter cars, they will reduce society's overall safety.
The committee's report suggests that future downsizing due to raising CAFE standards need not have such consequences. To me, this sounds a little like Dr. Samuel Johnson's description of a second marriage as "the triumph of hope over experience." It rests on the hope of technological improvements, but these are largely irrelevant to the core safety issue. Better engines, materials or crash avoidance won't alter the basic fact that risk is lower in heavier, larger vehicles. Even the tobacco industry never claimed that smoking risks could be canceled by new medical therapies such as cholesterol-lowering drugs.
The conclusion that CAFE increases traffic fatalities does not necessarily make it unacceptable public policy. But let's be honest about its safety implications. The technical picture is clear - CAFE kills, and more stringent CAFE standards will kill even more.
Dr. Leonard Evans is president of the International Traffic Medicine Association, former president of the Association for the Advancement of Automotive Medicine, and author of the widely acclaimed 1991 book, "Traffic Safety and the Driver."