The Bush administration announced new fuel economy rules Tuesday that require improved mileage for the sport/utility vehicles and other light trucks that have captured a majority of U.S. auto sales. Speaking from Atlanta, Department of Transportation Secretary Norman Mineta and Jeffrey Runge, the current administrator of the National Highway Traffic Safety Administration, said that under the new plan, the light truck segment will be broken into six different categories based on weight and vehicle type, with the smallest vehicles forced to get better mileage than larger ones.

NHTSA says it opted for using footprint size rather than vehicle weight or vehicle shadow for several reasons, one of them being that vehicle weight could be tailored more easily than size to move vehicles into heavier weight categories with lower CAFE targets.

Weight could be added to a vehicle near the edge of a category with minimal impact on design or performance at relatively low cost. Similarly, vehicle shadow (in a size-based system) could be tailored for the same purpose by the simple addition of bumpers or other vehicle lengthening features.