It used to be so simple. Divide the miles you drove since the last fill-up by the amount of fuel you just put in the tank, and there you have it — your average MPG for that distance.

Not anymore. Say you have a hybrid vehicle. These have internal combustion engines or ICE, as hybrid fans call them (is displacement specified in ICE cubes?), that typically don’t run 100% of the time. In certain circumstances, propulsion is by an electric motor supplied by an onboard battery pack. At a stop, everything shuts off. The electric motor means the ICE can be smaller. This factor combined with part-time operation mostly explains hybrid MPG ratings and low fuel costs.

To some people, anyway. There are those who believe that the cost accounting should consider much more than fuel consumed and miles traveled. Add to this, they say, such things as the energy costs of manufacturing the batteries, mining the nickel and other metals used in their construction and battery disposal.

Here’s how the balance sheet looks to The Recorder, Central Connecticut State University’s student newspaper. A recent editorial headline provocatively states that “Prius Outdoes Hummer in Environmental Damage.”

How’s that? The Recorder claims that “When you pool together all the combined energy it takes to drive and build a Toyota Prius, the flagship car of energy fanatics, it takes almost 50% more energy than a Hummer — the Prius’s arch nemesis.

“Through a study by CNW Marketing called ‘Dust to Dust,’ the total combined energy is taken from all the electrical, fuel, transportation, materials (metal, plastic, etc) and hundreds of other factors over the expected lifetime of a vehicle. The Prius costs an average of US $3.25 per mile driven over a lifetime of 100,000 miles — the expected lifespan of the Hybrid.
“The Hummer, on the other hand, costs a more fiscal $1.95 per mile to put on the road over an expected lifetime of 300,000 miles. That means the Hummer will last three times longer than a Prius and use less combined energy doing it.

“So, if you are really an environmentalist — ditch the Prius.”

But wait, Prius fans sputter; the assumptions are all wrong. Possible. For example, CNW Marketing — whoever that is — apparently didn’t run the numbers for equivalent lifespans. Or maybe they did, and the results didn’t carry the same magnetic attraction to controversy-consuming media.

But the point remains — how do you go about calculating the true cost of transporting yourself a given distance via motor vehicle? Even among motor fuels, what about the subsidy cost of ethanol? Do you discount the energy density difference between gasoline, E10 and E85 (aka Flexfuel)? Should you compare on the basis of fuel consumption per “seat mile?” On that basis, by the way, a Boeing 747 carrying 500 people beats out the Prius carrying two people. It can be shown that the 747 is getting 100 miles per gallon per person (at 550 mph!).

When you’re car-shopping a few years from now and trying to choose from cars that run on Flexfuel, biobutanol (coming soon), fuel cells (coming later) or whatever else is commercial by then, the fuel-economy numbers on the sticker may have disappeared along with their usefulness as a comparison to energy-conscious consumers.

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