Using less fuel can help the environment. Many people would like to use less for another reason as well.

Gasoline costs money, and the price tends to keep going up. Sometimes it does go down. But over the long term, the price tends to gradually go up. A common way of telling how well, or efficiently, a car uses gasoline is to look at its fuel economy. This is the number of miles it can go on 1 gallon. (A mile is about 1.6 kilometers.)

Partly this depends on how the car gets its power. Hybrids can use less gasoline because they get some of their power from electricity. Mileage per gallon also depends on the car’s weight. It takes more energy to move a heavy car than a light one. The shape of the car is another factor. A moving car pushes against the air, and this takes energy. Some shapes have less “drag.” They slip through the air more easily than others. Factors like these explain why different cars—even different hybrids—don’t all get the same number of miles per gallon.

Hybrids, such as those
being driven in New York
City, usually use less
gasoline in city than in
highway driving.

Grading Cars for Fuel Use
If you want to compare different cars, mileage figures from the EPA can help.

The agency measures all cars the same way. It found that the 2009 Toyota Prius could do 48 miles per gallon (20 kilometers per liter) in city driving and 45
miles per gallon (19 kilometers per liter) on the highway. Traditional cars usually get better mileage on the highway than in the city. The Prius does better in the city because it uses its electric motor more there.

In the United States the average fuel usage of new cars has to be better than a certain level. A 2007 law said this level will rise to 35 miles per gallon (14.9 kilometers per liter) by the year 2020.

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