Safety has long been a hot topic in debates over increasing fuel efficiency, but this is less so today. In 2002, Senator Trent Lott warned of ‘purple people-eaters’ (read: silly-looking golf carts) taking over the market if CAFE standards were raised; Mr. Lott now drives a Mini Cooper. Effective occupant protections are proliferating, and U.S. vehicle fatalities continue to decline.
Manufacturers are improving fuel efficiency through a host of strategies that include reducing vehicle weight by removing unnecessary material and substituting lighter materials, which in turn permits downsizing of the engine and other components. Ford, for example, has indicated its intention to reduce the weight of its vehicles by 12 percent on average by 2020. As a rule of thumb, each 10 percent reduction in body weight can lower fuel consumption by 6 percent when component downsizing is taken into account. None of this means changing vehicle dimensions – there’s no need to sacrifice protective crush space to get a more fuel-efficient ride, especially when today’s CAFE standards require smaller vehicles to meet tighter fuel efficiency targets.
At this point, weight reduction is one of the least expensive approaches to saving fuel. Composites such as carbon fiber-reinforced polymers remain expensive for the time being, but lightweight steel, aluminum and other plastics are pressed into service in vehicle configurations that frequently yield net cost reductions. The need to retool and to master challenges such as joining dissimilar materials mean the transition to lighter vehicles is gradual. But there appear to be few obstacles to a long-term trend toward substantially lighter vehicles. The trend will be especially helpful to the adoption of electric vehicles, for which downweighting is critical due to its implications for sizing costly batteries.
There may be a limit to prudent downweighting, but as the fleet turns over and collisions between vehicles of widely disparate weights occur less frequently, any such limit would shift as well. Moreover, as drivers accept increasing automation of vehicle controls, in particular collision prevention, driving around surrounded by a couple tons of metal will begin to feel very 20th century.