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Updated Automatically on June 26th, 2009
better gas mileage

If you’re like most people, your gas mileage is nothing like the “EPA Estimated Mileage” for your vehicle. Here’s why.

Oddly enough, the Environmental Protection Agency gas mileage tests don’t actually measure the gas mileage of a car directly, as described in the Gas Mileage Calculator article. Instead the EPA drives cars on a standard course and measures the exhaust emissions while they’re driving. They take those measurements and estimate gas mileage based on them. The EPA has to test a lot of cars and this is a simple, repeatable test that they can do quickly on each car. The problem is that it’s not representative of actual driving conditions and the numbers they get usually are significantly higher than the gas mileage you’ll get when driving.

The EPA tests were originally developed in the 1960s. Since then our driving habits have changed considerably. We now have multi-lane highways that run through and around most major cities. We have drive on more superhighways at higher speeds. We have more traffic jams. The EPA “City” gas mileage test consists of driving an 11 mile loop at an average speed of 20 MPH with 23 stops and five minutes of idling. Their “Highway” gas mileage test is a 10 mile loop at an average speed of 48 MPH with no stops and minimum idling time. I don’t know about you, but if I tried to drive 48 MPH on a highway, I’d probably get hit from behind! And do you really drive shorter distances on the highway than in the city?

Since the tests are standardized and they’ve been used to measure and compare hundreds of cars over several decades, the EPA isn’t going to change them. They did try to adjust for modern driving conditions in 1985 when they kept the test the same but reduced the estimated gas mileage figures. That helped a little, but most people still find that the EPA estimated numbers are higher than real world gas mileage.

You should be able to use the EPA mileage figures to compare mileage between cars (except hybrid cars, whose emissions characteristics seem to throw the EPA tests off by quite a bit) but don’t expect to actually get the EPA rated gas mileage in real world driving.

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Updated Automatically on June 26th, 2009
better gas mileage

One Response to “Why Your Gas Mileage Doesn’t Match The EPA Numbers”

    […] If you’re looking for a new vehicle, remember to take gas mileage into consideration in your choice. Remember that you probably will get lower real world mileage than the EPA rating though. It’s much easier to plan for good gas mileage up front by selecting a fuel efficient vehicle than it is to try to adapt an inefficient vehicle to try to get good gas mileage. […]

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