Measuring Fuel Efficiency

Is there a better way to measure fuel efficiency?  You know - mpg's.  We all use mpg's to compare cars or trucks and figure out which will use less fuel.  If I were comparing two cars whose ratings were 15 and 20 mpg, I would say the 20 mpg car had a big advantage in efficiency.  But if I were comparing two cars who's ratings were 40 and 45 mpg, initially I would say that the 45 mpg car also had a big advantage over the 40 mpg car.  Right?  Well, not quite.

A better way to measure fuel efficiency is to calculate fuel used for a given distance.  Say we took an average year of driving - 12,000 miles per year.  How much fuel would these cars use?  Well, a car that gets 15 mpg would use 800 gallons of gasoline while a car that got 20 mpg would only use 600 gallons, a total savings of 200 gallons per year.  Quite a lot.  But now for the higher mileage cars.  A car that gets 40 mpg would use 300 gallons of fuel, while a car that gets 45 mpg would use 267 gallons of fuel for a total savings of only 33 gallons per year.  Not very much.

What does this mean?  It means that the more fuel that a vehicle uses, the more impact an improvement in fuel efficiency will have on your pocket book.  Meanwhile, the higher mileage models don't have as much savings to gain.  See the chart below and notice how the slope decreases as the mpg's increase.   In the real world, this means that the automakers who try to improve the mileage of the big vehicles are making the most impact (Tahoe Hybrid) while the smaller cars (Civic Hybrid) don't actually save as much because they already get such good mileage.

So think in terms of fuel used per year, instead of MPG.  It's a better way...