For years, the automobile industry has argued that congressional attempts to make cars and trucks more fuel-efficient would compromise passenger safety. The argument is based on the premise that the Corporate Average Fuel Economy (CAFE) standards imposed in 1975 resulted in a reduction of vehicle weights, which in turn caused about 2,000 traffic deaths a year that would not have occurred otherwise. But as Congress considers an energy bill that would further boost fuel economy—the combined average for cars and light trucks has been stalled at about 25 miles per gallon since the 1980s—transportation experts have disputed the contention that a lighter fleet would be less safe. What is more, new engine and transmission technologies could enable manufacturers to improve fuel efficiency without significantly cutting vehicle weights.

The current CAFE standards are 27.5 mpg for cars and 22.2 mpg for light trucks. In June the Senate passed a bill that would boost the fuel economy of new cars and trucks by about 40 percent. (In August the House of Representatives passed a bill that would leave CAFE standards unchanged; a House-Senate conference committee is expected to resolve the differences between the bills later this year.) Under the Senate proposal, the National Highway Traffic Safety Administration (NHTSA) would divide the fleet into classes based on size or weight and set fuel-economy standards for each class to achieve an overall average of 35 mpg by 2020. Tom Wenzel, a transportation scientist at Lawrence Berkeley National Laboratory, says the safety impact would depend on whether the regulations alleviate the present mismatch between cars and light trucks. According to Wenzel, the lower CAFE standard for trucks has fostered a proliferation of behemoth SUVs and pickups that cause thousands of deaths every year when they plow into cars.

A step in the right direction, Wenzel says, would be defining the vehicle classes by size rather than weight. Because the size of a vehicle’s “crumple zone” can be crucially important for protecting passengers in a front-end crash, automakers should be discouraged from shrinking cars to enhance fuel economy. The best solution would be incorporating lighter, high-strength materials into auto frames and bodies, which would allow manufacturers to slash weight without trimming the vehicle’s footprint.

Other experts note, however, that major weight reductions may not even be necessary. Says David Greene, a transportation researcher at Oak Ridge National Laboratory: “If manufacturers were to take the available technologies and apply them to fuel economy over the next 10 to 15 years, they could cost-effectively achieve a 40 to 50 percent improvement without making vehicles smaller.” For example, some car engines already have variable valve lift and timing, which provides greater control over the flow of air into and out of the combustion chamber; until now automakers have employed this system primarily to boost horsepower, but it can also be used to increase fuel economy.

Another promising technology is a camless engine, which opens and closes its valves by computer signals instead of connecting them mechanically, via cams and camshafts, to the crankshaft. Valeo, a French automotive company developing camless systems, estimates that the technology could raise fuel efficiency as much as 20 percent. Innovations in transmissions, aerodynamics, tires and power-hungry accessories such as air conditioners can also upgrade fuel economy.

Greene predicts that the expense of meeting the new CAFE standards proposed in the Senate bill would probably range between $1,000 and $3,000 per vehicle, an up-front cost that could be recouped in fuel savings within five years if the price of gasoline remains above $3 a gallon. At the same time, the NHTSA could reduce the number of traffic fatalities by requiring the wider adoption of new safety features such as improved seat belts. “What we need are better safety regulations,” Wenzel points out, “not inaction on CAFE.”