Bigger Impact: 15 to 18 mpg or 50 to 100 mpg?

This is a pretty counter-intuitive statement, I believe:

You save more fuel switching from a 15 to 18 mpg car than switching from a 50 to 100 mpg car.

But some simple math shows it is true. If you drive 10,000 miles you would use: 667 gallons, 556 gallons, 200 gallons and 100 gallons. Amazing. I must admit, when I first read the quote I thought that it must be an wrong. But there is the math. You save 111 gallons improving from 15 mpg to 18 mpg and just 100 improving from 50 to 100 mpg. Other than those of you who automatically guess that whatever seems wrong must be the answer when you see a title like this I can’t believe anyone thinks 15 to 18 mpg is the change that has the bigger impact. It is great how a little understanding of math can help you see the errors in your initial beliefs. Via: 18 Is Enough.

It also illustrates that the way the data is presented makes a difference. You can also view 100 mpg as 1/100 gallon per mile, 2/100 gallons per mile, 5.6/100 gpm and 6.7 gpm. That way most everyone sees that the 6.7 to 5.6 gpm saves more fuel than 2 to 1 gpm does. Mathematics and scientific thinking are great – if you are willing to think you can learn to better understand the world we live in every day.

Related: Statistics Don’t Lie, But People Can be FooledUnderstanding DataSeeing Patterns Where None ExistsOptical Illusions and Other Illusions1=2: A Proof

3 thoughts on “Bigger Impact: 15 to 18 mpg or 50 to 100 mpg?

  1. This reminds me of the old saying that liars can figure, but figures never lie. While it is true that you save more gallons switching from 15 to 18 mpg than 50 to 100 mpg, the 50 to 100 mpg switch is a larger savings on a percentage basis. Is the question truly relevant? Why not just switch from 15 to 100 mpg?

  2. While the switch from 15 to 18 may save more gas, I think this is actually a good example of begging the question.
    The U.S., with 5% of the world’s population, consumes around 25% of the world’s petroleum, about half of that in the form of gasoline and diesel for vehicles. If everyone used gasoline like Americans do, there wouldn’t be enough to go around. In addition, we are all now aware that petroleum is being consumed much faster than it is produced (via natural processes). At current rates of consumption petroleum will probably be too expensive to use for cheap transportation within thirty years.
    The real question is not “which improvement saves more total gasoline,” but “how much gasoline can we afford to burn?” For instance, if we were to set a target of consumption commiserate with our population, reducing our consumption to 5% of the world’s total consumption, we would need vehicles with average fuel economies of around 130 mpg. If we want to double the length of time that we can afford to drive oil-powered vehicles, we need to double the fuel efficiency to about 45 mpg (assuming similar reductions in other oil-consuming industries).

  3. Pingback: Bad Math, Bad Statistics at Curious Cat Investing and Economics Blog

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