EPA economy ratings vs. the GM Volt: A square peg in a round hole

What a difference a number makes.

The projected EPA economy rating of the GM Volt has set off a storm of criticism across the Internet. While a number of blogs played the story straight, the Good Math blog attacked it as nonsense, which got picked up by Reddit. Critics say that the actual fuel economy seen by drivers could be as low as 50 MPG (the claimed figure for charge-sustaining mode), or as high as infinity. So who’s right?

Basically, they all are. The EPA city-cycle measures the Volt’s characteristics about as well as a square peg fits a round hole. In this mess, the number you get depends how you trim the test to fit the car.

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