The MPG Debate


Last week, I spent a little time talking about the differential effects of graphic versus text-only warning labels on cigarette packs.  Research verifies that the more jarring, graphic labels actually have a measurably increased affect on the reception and recognition of the message.  That is to say that the cigarette packages with a more graphic label increased public awareness of the side-effects of cigarettes smoke much more than did the text-only packages.

The lesson, I believe, is that science’s role in public policy isn’t limited writing the laws.  Science, in addition to providing data to form a good policy, also has an important role in communicating it to the public effectively.  The cigarette labels provide just one example that intelligently designed communication can significantly increase the effectiveness of a policy.

Another example of how more effective communication can affect policy arises with the way the fuel efficiency of our cars is displayed.  Right now the government mandates that the fuel efficiency of every car sold within the United States be displayed as estimations of both highway and city-driving miles-per-gallon (MPG), in an effort to promote purchasing more fuel efficient cars.  An article by Duke University professor Richard Larrick in the June 2008 issue of Science suggests that MPG might, in fact, be a little misleading.  Larrick argues that MPG misrepresents true fuel efficiency and that it might be causing consumers to make the wrong decisions when upgrading their automobiles.

He suggests that an alternative metric, gallons-per-mile or GPM, is, in fact, a better way to display the information.  Why is this so?  Perhaps its best to use an example.  If a family has two cars and is looking to replace one with a more fuel-efficient model, which is the better decision:  replacing a 34-MPG sedan with a 50-MPG hybrid or replacing an 18-MPG sport-utility vehicle with a 28-MPG model?  Intuitively it may appear that the increase in 16-MPG between the two sedans offers more savings The math, though, doesn’t back this up.

If each automobile was driven a distance of 10,000 miles, the 50MPG hybrid would use 94.1 gallons less fuel than the 34-MPG sedan.  Replacing the 18-MPG SUV with the model just 10MPG more efficient, though, would result in a fuel savings of 198.4 gallons over the same distance.  That’s more than twice as much in savings.  Larrick suggests that the surprise of this conclusion is the fault of the metrics we use to describe fuel efficiency.  He suggests that a conversion to gallons-per-mile would more accurately communicate the fuel savings between vehicles, and that improved communication would mean a more effective policy.

The cigarette pack example provides us with proof that, in some situations, a more effective strategy of communication can actually result in increased awareness and even altered behavior. It seems very reasonable then to suggest that more accurately and effectively communicating the fuel efficiency of cars could pay similar dividends.  In a world where greenhouse emissions and global warming are becoming increasingly salient issues, it seems very worthwhile to consider this option.




Good debate here. Well, when considering buying an hybrid car you will have to think of the upfront cost vs. the regular model. The hybrid cars tend to cost higher even tho they might save you gas in the long run, it takes many years to get your investment back on the hybrid. So depends how you drive and where you drive on the road and how long you are going to keep the car can determine whether you need an hybrid or not.

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