E-Letter responses to:

p-forum: Richard P. Larrick and Jack B. Soll ECONOMICS: The MPG Illusion Science 2008; 320: 1593-1594 [Summary] [Full text] [PDF]

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Published E-Letter responses:

The Math Is Trivial but the Impact Is Not

Dorian Driskell   (9 September 2008)

Moving Beyond Vehicle MPG

David R. Waldman   (7 July 2008)

The Math Is Trivial but the Impact Is Not 9 September 2008
Dorian Driskell Respond to this E-Letter: Re: The Math Is Trivial but the Impact Is Not	D. R. Waldman is correct that the math behind "The MPG Illusion" is trivial (Policy Forum, R. P. Larrick and J. B. Soll, 20 June 2008, p. 1593), however, the impact of "The MPG Illusion" is not. The enormity of the energy challenge is such that we must make intelligent decisions at both the societal and the individual level if we are to succeed. The stakes could hardly be higher—war or peace; poverty or prosperity. Society is unlikely to make intelligent economic decisions with regard to fuel efficiency if we continue to think in terms of miles per gallon (MPG), rather than gallons per mile (or liters/100km etc.). Until one overcomes this MPG mindset, it is not so obvious that it is far more pressing to give up one's 3-ton SUV than it is to convert an existing 45 MPG Prius to a 100 MPG plug-in hybrid. Certainly we will need those plug-ins soon enough. But we also need to prioritize our responses, or else face a bleak near-future. Dorian Driskell Los Angeles, CA, USA.
Moving Beyond Vehicle MPG 7 July 2008
David R. Waldman, Professor of Physics Borough of Manhattan Community College, The City University of New York, USA Respond to this E-Letter: Re: Moving Beyond Vehicle MPG	This article (Policy Forum, "The MPG illusion," by R. P. Larrick, J. B. Soll, 20 June 2008, p. 1593) points out something that those of us who teach physics see all of the time: students—and the general population—have a variety of misconceptions about everyday topics of interest. However, the revelation based on the fact that plotting gallons of gas used for a given distance versus miles per gallon (MPG) yields a hyperbola that is somewhat trivial in the light of the crisis based on the national consumption of gasoline. Using the authors' extreme MPG examples, we find that a vehicle that gets 12 MPG will use 833 gallons in 10,000 miles while a vehicle whose gas mileage is 50 MPG will use only 200 gallons for that same distance. That is, the 50 MPG vehicle uses 24% of the gasoline used by a 12 MPG vehicle traveling the same distance. The fact that equal increases in MPG produce smaller numbers of gallons saved as the MPG increases, while of possible interest to an individual driver, seems somewhat irrelevant for society as a whole. If we are to confront the dual problems of pollution and diminishing crude oil resources, it seems that large improvements in fuel economy are required. David R. Waldman Department of Physics, Borough of Manhattan Community College, The City University of New York, New York, NY 10007, USA.