Ann Arbor, Michigan – The current standards of the U.S. Corporate Average Fuel Economy (CAFE) create a financial incentive for automakers to produce bigger vehicles that are allowed to meet lower efficiency targets, according to a new study by the University of Michigan.

Over their lifetimes, these vehicles could produce carbon emissions similar to between three and ten 1,000-megawatt coal-fired power plants.

“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,” said Kate Whitefoot, who conducted the research. “The results show that the policy can be adjusted to reduce these unintended incentives by making it harder to lower the fuel economy targets by producing larger vehicles.” 

The standards are expected to require that automakers boost their average fuel economy to 35.5 mpg (6.7 L/100 km) by 2015, and 54.5 mpg (4.4 L/100 km) by 2025. However, these are averages, and in reality, each car company must meet a different standard each year as determined by the footprints of the vehicles it makes. According to the study, the sales-weighted average vehicle size in 2014 could increase by one to 16 square feet, undermining fuel economy improvements by between 1 and 4 mpg.

The footprint-based formula was set in 2006 to prevent an influx of smaller vehicles, as critics worried that the CAFE average would reward production of smaller, lighter vehicles that could disadvantage the domestic industry and possibly risk occupant safety.

The researchers have found that light trucks may grow even more than cars.

“Sustainability is about trade-offs,” said Steven Skerlos, an associate professor at the university’s Department of Mechanical Engineering. “On the one hand, there’s a concern about vehicle size largely driven by safety and the effect on domestic automakers. The adjustment to the CAFE standard tries to achieve high fuel economy while not compromising vehicle size, and the idea here is these things intersect and you have an equivalent of three to ten coal-fired power plants hidden in that trade-off.”

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