A University of Michigan study found larger vehicles, in aggregate, would generate between three and 10 1,000-megawatt coal-fired power plants' worth of excess carbon emissions during the lifetime of the vehicles..
"This study illustrates that there may be a substantial financial incentive to produce larger vehicles, and that it can undermine the goals of the policy," Kate Whitefoot, who conducted the study while a UM doctorate student, said in a UM release Thursday.
The loophole is the CAFE formula for setting mile-per-gallon targets, which are averages for all of a manufacturer's vehicle models.
Each car company must meet a standard each year determined by the literal "footprints" of the vehicles it makes, determined by track width times wheelbase, and larger vehicles allow an automaker to lower their average fuel economy targets.
The rationale for the footprint-based formula, created in 2006, was to prevent an influx of smaller vehicles, as critics worried the previous one-size-fits-all standard unfairly -- and perhaps dangerously -- rewarded production of slimmer, lighter vehicles that could put the domestic industry at a disadvantage and drivers at greater risk, the study said.
A sales-weighted average vehicle size in 2014 could increase by 1 to 16 square feet, undermining CAFE fuel economy improvements between 1 and 4 mpg, the researchers said.