MPG: 54.5 is the 37 to 39

Why advertised mpg doesn't match what you drive. One hint: it's not designed to.

Kai Ryssdal: There's a case in California small claims court today which hinges in part on this question: What's the definition of 50 miles per gallon? You'd think it's 50 miles driven for every gallon of gas, right?

The plaintiff's Hybrid Honda Civic only got 30, she says, so she's suing. But really -- does anybody actually ever get the advertised gas mileage?

Marketplace's Adriene Hill reports.


Adriene Hill: The short answer is yes: perfect people, living in a perfect world.

Phil Reed: People will get the advertised mileage only under very perfect conditions.

OK, very perfect people, living in a very perfect world. Phil Reed is with auto website Edmunds.com. He says it’s important to know that mpg is a range—city driving at the low end, highway driving at the high end, and most of us will wind up in the middle.

Researcher John DeCicco at the University of Michigan, says sticker mpg is best thought of in relation. Say you’re choosing between two cars: one advertised mpg of 30, another with 33.

John DeCicco: The odds are very very good that you’re going to get better mileage in the 33 mile per hour vehicle. That doesn’t mean you’re going to get 33 though.

Now, there’s added confusion here. Those new federal standards you’ve heard about -- 54.5 miles per gallon by 2025 -- those are based on a different set of mpg estimates even less connected with reality. DeCicco estimates that when they’re in place, it’ll mean we’ll be driving around in cars that get mileage in the high 30s.

Back at Edmunds, Reed tells me drivers who want to increase their fuel efficiency should be more -- you guessed it -- perfect. No quick acceleration. No slamming on the breaks.

At least that’s the idea.

Reed: Sometimes they continue to drive aggressively, but when gas prices go high, they know where to go for real savings.

Hill: So if gas prices get really high, we’ll have highways full of very docile drivers.

Reed: Wouldn’t that be nice?

A person can dream.

I’m Adriene Hill for Marketplace.

About the author

Adriene Hill is the senior multimedia reporter for LearningCurve.

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