Miles per Gallon vs Gallons per Mile

I read this article at HybridCars.com regarding how in America, we look at Miles-per-Gallon (MPG) as opposed to how many Gallons we use per mile (GPM).

In the article, it states how "most people ranked an improvement from 34 to 50 mpg as saving more gas over 10,000 miles than an improvement from 18 to 28 mpg," when in actuality that isn't true. Let's look at why it isn't.

I get that
10,000 miles / 34mpg = 294 gallons used,
10,000/50=200
shows a difference of 94 gallons saved...

and
10,000/18=555
10,000/28=357
shows a difference of 198 gallons saved...

The problem is that I think the point they're trying to make is this: 200 gallons used /294 gallons used = only a 32% reduction in fuel usage switching from a 34mpg to a 50mpg vehicle, while 357 gallons used / 555 gallons used = a 36% reduction in fuel usage switching to a more economical SUV. The percentage of reduction in fuel usage is higher with the 10 mpg change than the 15 mpg change. That doesn't come across to clearly, though.

But that's still not the point (I don't think).

The get-to-the-bottom-line point is: with a higher percentage of reduction in fuel usage over 10,000 miles, the SUV driver will spend $792 (with gas at $4/gallon) by making a 10mpg change in vehicles from $2,200 to $1,480. This as opposed to the $376 the 15mpg change will save the other person ($1,176 to $800).

So they're saying: "you don't have to turn in your SUV and get a Prius; even a small change to a higher mpg vehicle will burn less gallons per mile and save you more money at the pump."

Well...duh?

Honestly, anything that gets better gas mileage OR gets to 10,000 miles using less gallons is going to save fuel in the long run.

But their idea is best described in graphical form:



As you can (kind of) see, as the MPG gets higher from left to right, there is a significant cost difference when you go from 10mpg to 20mpg, as opposed to 40mpg to 50mpg; the chart basically starts to level off the farther right you go. We could essentially continue this out to the right where we would be getting 10,000mpg (so it would cost you $1 to go 10,000 miles), but you should get the picture.

Of course, it's a good idea to try and get the person in the H2 Hummer thinking about how much they could save by just switching to an H3 (going from 7mpg -> 14mpg would be a $2,850 savings in gas over the 10,000 miles), but are that many people who bought a Hummer really thinking about cutting their gas bill in half? Maybe.

But think about this: Over the course of the 10,000 miles, it would take 200 gallons of gas with the 50mpg Prius as opposed to 555 gallons with the 18mpg Tahoe. So if each of us drove Priuses, we'd each use 355 less gallons of gas every 10,000 miles. In pocketbook dollars (at $4/gallon), that's $1,400 a year. If the Hummer H2 driver isn't concerned about a $2,850 difference, are Tahoe drivers going to be concerned about a $1,400 difference?

Maybe. The bottom line is that less gas used = less cost. So whatever way people think about it, be it in miles-per-gallon or gallons-per-mile or in dollars-and-cents, we need to change our ways and use less gas.

That's what we should all be striving for.