This week, the Obama administration proposed new federal fuel-efficiency standards for motor vehicles that would make the current standards — known as Corporate Average Fuel Economy, or CAFE, standards — significantly more stringent. These CAFE standards measure compliance as the average of a company's entire fleet of cars, and so are better than model-by-model standards, both for lowering production costs and for matching consumer preferences.
Stavins, Robert N. "Obama's Fuel-Efficiency Plan? Not So Efficient." NPR.org, May 20, 2009.