Federal regulators will announce this summer a proposed overhaul of vehicle fuel economy standards that would base the rules on weights of vehicles - not whether they are cars or trucks, according to USA Today. The new system, which would take effect in 2007, would end incentives to automakers to build the smallest cars and biggest trucks, the newspaper said. Automakers are now required to meet a 27.5 mile-per-gallon fuel economy average for all the cars they sell, 20.7 mpg for light trucks - pickups, SUVs and minivans. The Corporate Average Fuel Economy (CAFE) standards have been based on separate car and truck averages since they became law in 1975. Because the new rules would group vehicles by weight, automakers wouldn't necessarily need tiny cars to balance bigger ones, USA Today said. Some Bush administration officials are worried that the current rules encourage automakers to sell smaller cars, according to the newspaper.