Pun Salad Does the Math

David Brooks, aka Granite Geek, grabs gas mileage data points as he navigates a short section of the F. E. Everett Turnpike in his Honda Civic hybrid.

After the first two three days, the results on the 5.4-mile stretch are:

at 59 miles per hour* - 63.5 MPG
at 60 miles per hour - 63.1 MPG
at 70 miles per hour - 54.8 MPG

See his article for details and caveats. But it occurred to me to ask some obvious questions:

How much difference in gas consumption is that? Well, between his 59MPH and 70MPH datapoints:

(5.4 miles/54.8 mpg - 5.4 miles/63.5 mpg) = 0.0135 gallons

How much money is that? Let's say gas is (moan) $3.50/gallon; that works out to

0.0135 gallons * $3.50/gallon = about 4.7 cents

How much time is lost? That would be:

(5.4 miles/59 mph - 5.4 miles/70 mph) = 0.0144 hours = about 52 seconds

So: is it worth 4.7 cents to shave 52 seconds off your drive time? As they say, your mileage may vary.

Ah, (you say) but the money adds up! But so does the time. Let's do the same calculations over 70 miles instead of 5.4:

money savings: 
    $3.50/gal * (70 mi/54.8 mpg - 70 mi/63.5 mpg) = 61 cents

time savings = 
    (70 mi / 59 mph - 70 mi / 70 mph) = 11 minutes

You have to drive about 375 miles before you save a whole hour at 70mph as opposed to 59mph. Using David's fuel economy numbers, you'd be buying slightly under a gallon of gas for that time savings, about $3.28 worth.

Drivers make their own calls on the time/money tradeoff but, even with high gas prices, it's not surprising that a lot of them would prefer to zip along at 70.

Monster.com has an illuminating article on cutting one's commuting costs. There's a lot of common-sense advice; e. g., keep your tires properly inflated. There are a number of suggestions where the tradeoffs in time and convenience are elided, e. g. pooling, mass transit. And finally, there's advice on looking for government/employer subsidies: in effect, getting other people to pay for your commute. Good luck with that.

Finally: I would have to turn in my Official Libertarian Propeller Beanie if I didn't point out good articles from Heritage, Cato, and CEI detailing why government-mandated fuel economy standards don't help the environment, don't save energy, but do nudge us into vehicles more likely to kill us. Unfortunately, Congress and the President ignored this advice; higher standards are on the way.

Last Modified 2012-10-12 8:25 AM EST