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MPG vs GPM: Should America Make The Switch?


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Apart from eating mayo with their french fries, driving a bunch of tiny little diesels, and idolizing Abba and David Hasselhoff, what's the big difference between a European and an American? Over at Green Car Reports, Editor-in-chief John Voelcker outlines the GPM vs MPG debate. As in Gallons Per Mile vs. Miles Per Gallon. Actually, everywhere outside the U.S. (including Canada), they typically calculate using the metric system, so it's more like liters per 100 kilometer (L/100km).

But we're iconoclasts in America. You know, Mavericks. So we've resolutely stuck to our MPG measurement system, which Voelcker points out has led to a big misperception of fuel consumption. His article explains that taking even small steps can help you make a big difference in U.S. energy consumption.

Voelcker poses the question:

Which saves more gasoline, going from 10 to 20 mpg, or going from 33 to 50 mpg?

He claims that a majority of Americans pick the second as the more fuel-stingy route, but points out that the first is actually more frugal. In fact, believe it or not, going from 10 to 20 mpg saves fives times as much fuel as going from 33 to 50 mpg. As well, most Americans simply aren't going to trade their Suburbans for hybrids overnight or even in the next decade.

Voelcker points out that calculations using gallons-per-mile helps illustrate that replacing a guzzler (you know, like your 9 mpg Hummer H2) with a car that consumes moderately - say averaging 20 mpg - makes a dramatic difference in CO2 emissions, to the environment, in reliance on foreign oil, and of course to PSQ (personal smug quotient).

In fact, Voelcker claims that if the vast majority of us replaced gross consumers with moderate consumers, we'd have a much bigger impact on gas consumption and the environment than trying to displace traditional vehicle sales with hybrids. Surprisingly, it turns out that in the last 10 years, the U.S. has only managed to replace three percent of total vehicles sold with hybrids. Hybrids are important technology, to be sure, but apparently they've yet to make a big impact on the environment.

The root of the problem seems to be the assumption that consumption is reduced at a steady rate as mileage is increased; i.e., a directly inverse relationship. But it turns out that, upon more thoughtful examination, this just ain't the case. Voelcker directs readers to a Website, The MPG Illusion, that explains the issue in detail.

So how about it, 'murricans? Is it time to switch from MPG to GPM? I think we'd have to vastly improve our public education system first or risk some sort of mass hysteria...

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Comments (7)
  1. "doesn't make much diffference"

    MPG is used by consumers to compare mileage between vehicles and that's the measurement that matters to them. It's easier to arrive at your cost per mile using MPG.
     
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  2. "mileage"

    Prioritization is the key. Major decreases in fuel consumption would be realized by targeting markets that drive the most miles--commercial diesel trucks. Old diesel trucks/buses should also be pushed out of use due their horrendously polluting engines. Ditto for cars older than 1980. Financial incentives are the way to go, rather than diktats.
     
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  3. "Mr."

    I think switching would be a good idea, though educating about the change would be crucial. In the first question, most folks wouldn't stop to think that going from 10 to 20 mpg is a 100% increase and going from 33 to 50 mpg is just under a 50% increase - they just see difference between the 2 sets of numbers 10 vs 17. GPM would more cleary show the difference. Still, it's not likely to change.
     
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  4. "Metrication"

    How about we cut to the chase and move the country to the metric system? Most people don't seem to know much about the US Customary system anyway. After that we could make the transition to L/100 km
     
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  5. "Don't do it"

    We use metric like rest of the educated world but one area it sucks is in Litres/100Km, it is a pain to calculate that in real world figure. MPG is much easier, stick to it.
     
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  6. "Response to R2dad"

    I think you're right about the need to upgrade the truck fleet. Here's an idea, rather than rebuild the nation's highways improve them so that they can deliver electricity to big rigs. The energy cost of electricity is about 1/6 the cost of gasoline so with such a huge reduction in fuel cost every trucking company would be forced to buy an electric truck.
     
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  7. "Response to 1 and 2 and 6"

    "It's easier to arrive at your cost per mile using MPG."
    By definition, cost per mile has mile in the denominator.
    GPM times the cost of gas = gas cost per mile.
    Gallons per 100 miles times the cost gas = gas cost per 100 miles.
    Etc.
    GPM is gas consumption. We don't need more education if we used GPM instead of MPG.
    Metric versus imperial are two different issues. The issue is whether consumption or distance is in the numerator.
     
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