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Hold on a second … there’s a problem with the impressive claim made by Chevrolet last week of 230 miles per gallon for its electric Volt model (which is still under development). Actually, two problems.

The first is how to measure the miles per gallon of an electric car. As has been noted in a number of other blogs such as EcoGeek and Good Math, Bad Math, using mpg for electric cars is “far from ideal” (remember — the Volt still uses electricity from coal-fired power stations to recharge its battery).

There’s also the the troubling assumption that, for the first 40 miles after a charge, the Volt doesn’t use any gas — and so gets an infinite mpg! Kinda silly. A true estimate of mpg for the Volt is probably around 100 mpg (which is highly dependent on the length of your commute and whether you can be bothered to plug it in every night).

But even at 100 mpg, should we be SO impressed? And if not, why? That gets to my second problem — the measurement of car mileage itself. And this issue  goes for all cars — normal, hybrid and electric.

Basically, the U.S. auto industry (and those who regulate it) are using a misleading measure of fuel efficiency. Instead of miles per gallon, we should be using the more logical gallons per (10,000) miles. (The rest of the world measures fuel efficiency this way, although generally in liters per x number of miles.)

Why? It’s really simple: For every apparent “doubling” in mpg, you are really only using half the amount of gas. Although this is still impressive, let’s not get sucked into believing the extravagant hype. I will use examples to illustrate the misleading part:

  • At 12.5 mpg (in your great-big-huge SUV) you will use 800 gallons to go 10,000 miles (and incur the wrath of tree-huggers);
  • At 25 mpg (a friendly sedan) you will use 400 gallons to go the same distance; and
  • At 50 mpg (a super-green eco-loving hybrid) you will use 200 gallons.
See the problem? While mpg has doubled each time, it’s the INCREMENTAL SAVING (sorry for shouting) of actual gallons that we should be paying attention to!

While 200+ mpg is impressive (50 gallons per 10,000 miles), the REAL SAVINGS (yes, more shouting) are at the lower end of mpg — in other words, getting the great-big-huge gas-guzzlers off the roads. This is because a vehicle that does 12.5 mpg versus 25 mpg saves 400 gallons of gas! While going from 25 to 50 mpg (“doubling”) only saves 200 gallons. To get even close to that original 400 gallons saving, we would have to go from 25 to 800 mpg!! (387.5 gallons of saving.) See?

So, with SUVs averaging 18 mpg (versus 24 mpg for regular cars), it’s much more important to get the 99 million SUVs and pick-ups off U.S. roads (or drastically increase their fuel efficiency) than it is to pour all this effort into producing super-high-fuel-efficient cars (that in reality barely sell in comparison to SUVs).

-- Text by Timothy Boucher, Cool Green Science Blog

For more: Read our transportation blogger Jim Motavalli's post, 'EV MPG showdown: Volt vs. Leaf vs. Mini E.'