Car Makers Get Their Wish on Fuel Efficiency Standard

One of the more complicated loopholes is related to the square footage of an automobile. Known as the “footprint” rule, it grades vehicle emissions on a curve by progressively lowering the fuel-economy requirement as a vehicle gets bigger. This means that as engineers redesign vehicles, they are rewarded for making them bigger and, theoretically, less efficient.
“Auto makers have an incentive to make more SUVs and light trucks with less stringent standards than high-performance sedans,” said Kate Whitefoot, an assistant professor of mechanical engineering and public policy at Carnegie Mellon University. She co-wrote a 2011 research paper predicting that migration toward larger vehicles.