GPM

Jake Yong reiterates the point made by Larrick and Soll in their article in Science that the way we consider vehicle fuel consumption hides significant improvements in efficiency for the more fuel hungry vehicles. The key is to consider not the distance per fuel consumed (miles per gallon), but the reciprocal, the fuel consumed per amount of distance travelled (gallons per mile).

For an example of my devising: which is the better improvement: changing a vehicle from 5 mpg to 8 mpg, or improving a vehicle from 10 mpg to 25 mpg? Consider these vehicles on a 200 mile trip. The first vehicle will initially use 200/5=40 gallons of gas on the trip, but after the improvement will use only 200/8=25 gallons, saving 15 gallons. For the second vehicle, we initially consume 200/10=20 gallons, and after increasing the efficiency, consume 200/25=8 gallons, for a smaller 12 gallon savings.
Thus a “small” improvement, as measured in mpg, for inefficient vehicles is actually a rather sizable fuel savings.