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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

Figure 1. SUVs are prone to roll overClick to Enlarge ImageThe cars and trucks plying America's roads and highways generate roughly 20 percent of the nation's total emissions of carbon dioxide, a pollutant that is, of course, of increasing concern because of its influence on climate. Motor vehicles also account for most of our country's dependence on imported petroleum, the price of which has recently skyrocketed to near-record levels. So policymakers would welcome the many benefits that would accrue from lessening the amount of fuel consumed in this way. Yet the fuel economy of the new-car fleet has not risen since the late 1980s, when it exceeded 27.5 miles per gallon (to meet standards enacted in the mid-1970s). Over the past two decades manufacturers have, for the most part, used advances in automotive technology, ones that could have diminished fuel consumption, to boost performance and increase vehicle weight. In addition, the growth in popularity of pickups, sport utility vehicles (SUVs) and minivans—and the large amounts of gas they typically guzzle—has resulted in the average vehicle using the same amount of fuel per mile as 20 years ago.

One of the historical impediments to imposing tougher fuel-economy standards has been the long-standing worry that reducing the mass of a car or truck to help meet these requirements would make it more dangerous to its occupants in a crash. People often justify this concern in terms of "simple physics," noting, for example, that, all else being equal, in a head-on collision the lighter vehicle is the more strongly decelerated, an argument that continues to sway regulators, legislators and many in the general public.

We have spent the past several years examining the research underlying this position—and some recent work challenging it. We have also conducted our own analyses and come to the conclusion that the claim that lighter vehicles are inherently dangerous to those riding in them is flawed. For starters, all else is never equal; other aspects of vehicle design appear to control what really happens in a crash, as reflected in the safety record of different kinds of vehicles. What's more, the use of high-strength steel, light-weight metals (such as aluminum and magnesium) and fiber-reinforced plastics now offers automotive engineers the means to fashion vehicles that are simultaneously safer and less massive than their predecessors, and such designs would, of course, enjoy the better fuel economy that shedding pounds brings.

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