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Today, the US Department of Energy published a notice of proposed rulemaking that would change the way the government calculates the energy efficiency of electric vehicles. If adopted, the changes will substantially downgrade the fuel-efficiency ratings given to EVs and be used to determine corporate average fuel economy (better known as CAFE). That might have serious implications for automakers, but don’t worry—the consumer-facing MPGe and kWh/100 miles numbers you see on Monroney window stickers and at the US Environmental Protection Agency’s fueleconomy.gov site won’t change.

They call it CAFE, but you can’t drink it

Congress enacted CAFE in 1975 in the wake of the country’s first serious energy crisis. It gives an average fuel efficiency number that each automaker must achieve to not be sanctioned by the government, and the standards and penalties are enforced by the National Highway Traffic Safety Administration.

But the fuel efficiency numbers that NHTSA calculates are much higher than the actual efficiency you or I might experience, or the numbers posted by the EPA for consumers to make buying decisions.