The idea behind fuel efficiency standards, nominally, is to end up with more efficient cars. But according to a new study from the University of Michigan, what they actually do is create a financial incentive for bigger cars — because bigger cars don't have to be as efficient. 

Fuel economy goals are stated as an average for the whole industry. But the guidelines actually vary by company depending on their vehicles' footprint, which is track width times wheelbase. Companies that make bigger cars can aim for a lower average fuel efficiency. This study found that average vehicle size could increase up to 16 square feet in 2014, with an attendant rise in carbon emissions:

Over their lifetimes, these larger vehicles would generate between three and ten 1,000-megawatt coal-fired power plants' worth of excess carbon emissions. A 1,000-megawatt plant could provide power for more than half a million people.

The rule where efficiency tracks with footprint was actually intended to prevent automakers trying to game the efficiency standards by making tiny cars. Because … lord knows we don't want tiny efficient cars?

The impetus for the footprint-based formula back in 2006 was to prevent an influx of smaller vehicles, though not necessarily to do the opposite. Critics worried that 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 researchers believe the correction overshot its target.

So now there's an economic incentive to game the system by making GIANT cars, which puts the entire planet at greater risk. Awesome.