Out with mpg?

In Europe, gas mileage is expressed in liters per 100 km. Growing up with miles per gallon (mpg), this was a double assault on my abilities to convert units, and it never made sense to me.

RealClimate has a post on the case for going to the same concept in the United States: The mpg confusion. Using gallons per 100 miles, rather than miles per gallon, actually allows for more meaningful and intuitive comparisons between cars. The current mpg system isn’t a linear relationship, which means that a small improvement at the bottom end (SUVs) actually makes a greater difference than a big improvement at the high-efficiency end (compacts).

Some advocate using gallons per 10,000 miles instead, as this gives the buyer an idea of how much gasoline will be used in a year.

This data table puts it all together, with a column added for gasoline cost per 10,000 miles (at $3.50 per gallon):

Car mpg gal/100 mi gal/10,000 mi cost per 10,000 mi
typical SUV 12 8.3 830 $2905
hybrid SUV 18 5.6 560 $1960
typical compact 25 4.0 400 $1400
hybrid compact (Prius) 46 2.2 220 $  770

If one were to replace their typical SUV with a hybrid SUV, the gas mileage increases from 12 mpg to 18 mpg. This six mpg improvement is actually more significant than the 21 mpg improvement one gets from replacing the typical compact with a Prius! This is especially evident in the last three columns of the table. The SUV buyer saves 270 gallons (or $945) every 10,000 miles by purchasing a hybrid. The compact car buyer saves 180 gallons (or $630) every 10,000 miles by purchasing a hybrid.

This is easier to see with gal/100 mi (or gal per 10,000 mi, or cost per 10,000 mi) than it is with mpg.

This also shows the importance of weaning our society off of non-hybrid SUVs.

Of course, the SUV driver would do even better to replace their car with something smaller. By replacing their SUV with a hybrid compact, they would save 610 gal, or $2135, every 10,000.

Grace and Peace

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