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Back of the Envelope

July 6th, 2009

So yesterday, in my post with the funny German title, I contemplated how much gas we could save if everybody drove a car with a manual transmission.  Someone told me later, “You asked the question, but you didn’t give us the answer!”  Well, I don’t know the answer, but it’s an easy calculation – at least if the goal is to get a rough estimation…  So, let’s do the math!

In 2007, according to the Bureau of Transportation Statistics, there were nearly 136-million registered passenger vehicles in the U.S.  These cars drove nearly 1,671-billion miles and consumed over 74-billion gallons of fuel that year.   This yields an average fuel economy of 22.5mpg.  If the 72% of vehicles that have automatic transmissions had manuals (with the assumption that their fuel economy would increase by 1mpg, to 23.5mpg), then it turns out we could save approximately 2.28-billion gallons of fuel a year, or about 3% of the fuel used for our passenger vehicles.  That translates to over 116 million barrels of oil per year, or in financial terms, $8-billion (at $70 per barrel).

…This is what I learned to do in graduate school…

Old School HP Calculator

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