Its Gallons Per Mile And Not Miles Per Gallon That Determines Fuel Economy

My comment to "How Do Consumers Spend Engine Efficiency Advances? On Bigger, Faster Cars" by Donald Marron:

Actually fuel economy would have increased by 37.8 percent. One should use fuel per mile and not miles per gallon to compute fuel savings. So for every 100 miles driven, at 23 miles per gallon, the car will us 4.35 gallons. At 37 miles per gallon, a car driven 100 miles will use 2.7 gallons. The fuel savings is 1.65 gallons per 100 miles or 1.65/4.35 or 38 percent fuel savings. The fuel savings is not the 60 percent as mentioned by Knittel. It is a common error caused in part by the unfortunate use by the EPA of miles per gallon instead of gallons per mile.

I am surprised AER or reviewers did not ask for a change.

Just think of an engine performance improvement from 30 mpg to 60 mpg. Under EPA and Knittel’s math that is a 100 percent energy improvement usage. In other words, the car no longer needs gas to run since it uses 100 percent less gas.

Gallons per mile does not increase as fast as miles per gallon. Going from 30 to 60 mpg is a 100 percent improvement in mpg but only a 50 percent improvement in gallons used per mile.

We care about the number of gallons of gasoline we use, gallons per miles, not mpg. Using fewer gallons is the energy efficiency and environmental goals.

If EPA used gallons per mile instead of mpg, consumers actually would see how few gallons we save in government mandated fuel economy measures for driving an a so called energy efficient auto.