A random diversion into energy policy and math

The Obama Administration will begin implementing rules requiring cars to get an average of 54.5 miles per gallon, up from 29.7 mpg today.  Allegedly, this will reduce our dependence on foreign oil.

Allegedly.  Unfortunately, we express fuel usage in miles per gallon, which makes sense if Americans use a constant amount of gasoline (i.e. the denominator is gallons of gasoline).  Flipping the number around and expressing it as gallons per mile, we can see how brutal the law of diminishing returns is when applied to fuel economy.

Let’s say that you travel 600 miles in a week.  A car that gets 15 mpg will use 40 gallons in a week. If your car gets 20 mpg, you’ll use 30 gallons of gas in a week.  Move that to 30 mpg, and you’ve saved yourself 10 gallons of gasoline.  In order to save an additional ten gallons, you’ll have to get a 60 mpg car.  Ergo, the gas savings from 15 to 20 mpg, 20 to 30 mpg, and 30 to 60 mpg are identical.

Which is to say: we’ve already squeezed a lot of our gas savings out of compact cars, sedans, and light trucks.  It’s just plain math: we would do better to change a 10 mpg truck to a 15 mpg truck than we would to change a sedan, travelling the same distance annually, from 29.7 mpg to 54.5 mpg.

This doesn’t relate to health care, except to underscore the point that if you don’t understand basic math, you cannot hope to set decent public policy.


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