This is a graphic treatment of an issue mentioned yesterday -- the somewhat misleading nature of the miles per gallon statistic. If you use MPG as your main metric of fuel efficiency, then a change from a 20 MPG vehicle to a 30 MPG vehicle sounds like a smaller advance than does a switch from a 40 MPG vehicle to a 60 MPG vehicle. But if you assume a constant distance to be driven, the former switch reduces fuel consumption more.
Now, obviously, a 20 MPG reduction is still better than a 10 MPG reduction, all else being equal. But "all else," crucially, isn't equal. You get much more bang for your buck by improving performance at the low end.
This article available online at:
http://www.theatlantic.com/politics/archive/2007/12/two-ways-of-looking-at-fuel-efficiency/47561/
