I didn’t know this: In Canada, automobile fuel economy is expressed as gallons per mile, not miles per gallon as it is in the U.S. (Well, really, it’s liters per hundred kilometers, but if you’re south of the 49th parallel and a metric-system-phobe, gallons per mile is essentially the same thing.)

Now, I don’t mention this just to expose my lack of cultural knowledge of my northern neighbors. I mention it because it seems to me that liters-per-kilometer is a much better way of expressing the fuel efficiency of autos.

As I mentioned before, miles-per-gallon math is quirky, and has all sorts of unexpected and counterintuitive consequences.

Among them: a seemingly huge upgrade in fuel economy (say, trading a Camry for a Prius, which doubles your fuel efficiency from 30 mpg to 60 mpg) can have the same fuel-saving consequences as seemingly smaller improvements among larger vehicles (say, trading a 15-mpg SUV for one that gets 20 mpg).

Using miles per gallon, that fact just seems strange — how can the huge jump from 30 mpg to 60 possibly have the same effect as the much smaller shift from 15 mpg to 20?

But if you use the Canadian method, there’s nothing counterintuitive or confusing. Shifting from a car that burns 4 gallons every 60 miles (i.e., 15mpg) to one that burns 3 gallons over the same distance (20 mpg) saves 1 gallon of gas every 60 miles: 4-3=1. Likewise, shifting from a car that burns 2 gallons per 60 miles (i.e., 30 mpg) to one that burns 1 gallon (60 mpg) saves 1 gallon over the same distance: 2-1=1. The math is much clearer, and any apparent "paradox" disappears.

Canadian fuel efficiency figures also makes it easier to tally the cost of fuel. With gas at $1 per liter, say, an 8 liter/100km vehicle costs $2 extra bucks every 100 km driven, vs. a vehicle that gets 6 liter/100km. So if you’re buying two cars, you may not even need to pull out a calculator to figure out how much the more efficient car will save you each year.

So I wonder how many Americans chose big, inefficient SUVs thinking (incorrectly) that there wasn’t such a big difference between 15 mpg and 20 mpg. I don’t know if using Canadian fuel economy math would have made their choices any different. But at a minimum, the cost consequences of their choice would have been a little clearer.