The data in this story come primarily from two government documents: "Notice of Proposed Rulemaking, Average Fuel Economy Standards, Passenger Cars and Light Trucks, Model Years 2011-2015" and "Preliminary Regulatory Impact Analysis, Corporate Average Fuel Economy for MY 2011-2015 Passenger Cars and Light Trucks." Both are available at the National Highway Traffic Safety Administration website.
To determine the "mileage gap" for each automaker, we calculated the difference between the company's own anticipated fleetwide miles per gallon in 2011—as provided to NHTSA—and the proposed new federal standard each company will have to meet. We expressed that difference as the percentage by which mpg will have to be improved to meet the new requirement.
Note: Data represent "adjusted baseline" mpg figures as computed by NHTSA, which account for certain manufacturers making minor technological changes to meet government requirements.