Fuel Meter

Richard Larrick and Jack Soll,two Duke management professors, demonstrated in an article (appeared in the June issue of Science magazine) that the commonly used Miles Per Gallon (MPG) measurement is misleading. They argue that the problem with MPG is that it leads consumers to significantly underestimate the reduction in fuel consumption that can be achieved by replacing very low MPG cars with the ones that go even only a few extra miles for the same gallon. Less detrimentally, this measure also misleads people to overestimate the benefits of replacing relatively fuel-efficient cars with more fuel efficient ones.

They illustrate this point by comparing number of gallons consumed by cars to travel 10,000 miles.
Example 1:
Consider two cars X and Y and lets assume X provides 10 miles per gallon and Y provides 12 miles per gallon. X would take 1,000 gallons to cover the distance while Y would take only 833.33 gallons. In other words, Y would save 167 gallons of gas (and $501.00 assuming a price of $3/gallon) for every 10,000 miles.

Example 2:
Consider same two cars X and Y. But, now lets assume X provides 25 miles per gallon and Y provides 30 miles per gallon. X would take 400 gallons to cover the distance while Y would take only 333.33 gallons. In other words, Y would save only 67 gallons of gas (and $201.00 assuming a price of $3/gallon) for every 10,000 miles.

It is important to note that in the first case, for an increase of 2 MPG, 167 gallons was saved. While in the later case, despite an increase of 5 MPG, only 67 gallons were saved.

They present the following chart that shows the relation between MPG and gallons consumed for covering 10,000 miles.


We created the following chart that shows the number of gallons saved per 10,000 miles by moving to a car that provides one additional MPG. For example, when a 10 MPG car is used instead of 9 MPG car, 111.11 (1111.11 - 1000.00) gallons is conserved. Similarly, by moving to a 11 MPG from a 10 MPG one saves 90.91 gallons.


The steep fall on the left side and the slow decline on the right side of the curve clearly indicate how misleading MPG can be, as argued by the aforementioned authors.

They recommend using an alternate unit of measure - Gallons Per Mile. We, like New York Times, agree that it is a great idea. However, we believe that the auto industry can clearly present the consumption information with a simple addition to cars - a fuel meter that shows a cumulative total of number of gallons consumed. We believe this meter can be added without any difficulty since most vehicles are already equipped with a fuel gauge.

Such a meter would let the owner/driver know the number of gallons consumed by that vehicle for the distance indicated by the odometer.