The "MPG Illusion"

Monday, January 5, 2009

If you're interested in fuel economy, either for environmental or economic purposes, you'd probably be interested in reading this article. It raises a very interesting mathematical point about the miles per gallon measurement: increases in your MPG do not give proportional decreases in fuel consumption. Or to put it more concretely, you save as much money switching from a 10 mpg car to a 15 mpg car as you would going from a 15 mpg car to a 30 mpg car!

Why is this? Well, if you think of it in terms of gallons per mile -- which tells you exactly how much fuel you consume as you drive -- rather than miles per gallon, you get the inverse of a linear function:



Note that the jump from 10 to 15 is the same as the jump from 15 to 30!

Just an interesting tidbit to consider before buying a car based on MPG.