Math Is Hard: MPG Still Stupid, National Research Council Agrees

By John Voelcker

1,172 views Jul 7, 2010

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More than a year ago, we wrote an article pointing out the flaws in the U.S. practice of measuring a car's gasoline use with the familiar miles-per-gallon (MPG) measure.

Now, no less a body than the august National Research Council has agreed with us.

As  it noted in a pre-publication summary released by the National Academy of Sciences:

Fuel economy data cause consumers to undervalue small increases (1-4 mpg) in fuel economy for vehicles in the 15-30 mpg range.

Display consumption as well as MPG

Its panel strongly urged that the information should be displayed to consumers as fuel consumed (volume of fuel per 100 miles, for example) alongside the traditional MPG measure, which is only really used in North America.

Everywhere else, car buyers assess and compare consumption, which correlates directly to their fuel costs (as well as tailpipe emissions of greenhouse gases, predominantly carbon dioxide).

So what, exactly, is the problem with good old American miles per gallon? We laid it all out more than a year ago in an article entitled Miles Per Gallon Is Just Stupid; No, Really, It Is.

It's not linear

To illustrate the problem, just answer this question: Do you save more gasoline by going from 10 to 20 mpg, or going from 33 to 50 mpg?

Most Americans pick the second choice. But that's wrong. No matter how many miles you drive, swapping out a car that gets 10 mpg for a 20-mpg version will save you five times the amount of gasoline that going from 33 to 50 mpg will. Five times!

The problem is that the MPG scale isn't linear. A 10-mpg improvement saves vastly different amounts of gasoline, depending where on the scale it falls. But fuel consumption (gallons used to go a set distance) is linear. Halve that number, use half the gasoline.

And if you still don't believe us, read the entire original article--which caused, ummmm, quite a lot of controversy when we first published it, and continues to generate readership and interest.

Sorry, folks. Math is math. Even if, to quote Barbie, "Math is hard!"

Three-year study

The NRC panel's three-year study, done at the request of the National Highway Traffic Safety Administration (NHTSA), investigated  the merits of different methods for improving gas mileage over a base 2007 vehicle.

As well as the MPG recommendation, the report concluded that a combination of existing technologies could meet the now-enacted increases in corporate average fuel economy (CAFE).

But it also noted that making cars more fuel-efficient would raise their cost, and that the payback for such measures depended entirely on the future price of gasoline.

[The Car Connection]