Miles Per Gallon. Old Fashioned.
Meet MPD, or Miles Per Dollar. MPD is more useful than MPG for a couple of reasons:
1) It gives a realistic sense of what you are spending.
2) It makes it easier to compare the cost of vehicles that use different energy sources.
If you want to calculate your MPD, read on!
Step 1: When Would You Use MPD?
It is useful to use MPD when you are shopping for a new car. A prospective buyer can calculate his MPD for his current car, and compare it to that of a new car and see if he would be saving money.
Say Rick currently owns a 1995 Ford Taurus as his daily driver. It has been reliable since day one, but it only gets 18 MPG combined. Rick is looking at a new 2014 Toyota Camry that gets 25 MPG.
Using that information, it is clear to see that Rick will save gas money by buying the Camry because he can go 7 extra miles per gallon of fuel he buys. But what happens if he wanted to buy a Volkswagen Jetta TDI? (Diesel)
Well, that is when MPD comes in.
Step 2: Here's How
Rick's Ford Taurus gets 18 mpg. If gas is $3.50 in his town, then to go 18 miles costs $3.50.
MPD = M/D Where M is miles traveled and D is dollars spent.
So the MPD for his Taurus is 18/3.50, which is 5.14.
A VW Jetta TDI gets 34 mpg. But gasoline isn't the same price as diesel fuel in most places. So you can't just compare the mpg ratings. This is when you would use MPD as a more useful comparison. Diesel fuel in Rick;s town is $4.10.
MPD = M/D
MPD for the Jetta TDI is 34/4.1, which is 8.29.
Compare those two MPD numbers, and you can see that for the same dollar, Rick will go farther in the diesel than his current gas car. For every 5 miles he goes in his Taurus, he could go 8+ in a Jetta.
Step 3: Electricity, Anyone?
Tesla Motors is a company you have probably heard of if you are reading this. I think they are awesome, and that electric cars and even trucks are the future. Rick thinks so too, so he found out via http://www.teslamotors.com/goelectric#savings that if electricity is 11 cents per KWh, then the cost to drive a model S 100,000 miles is $3,113. Rick's electricity is 11 cents per KWh, so that is correct for him.
MPD = M/D
100,000/3,113 is 31.12.
This electric car goes 31 miles per dollar. That is a huge improvement over his Taurus' 5.
Step 4: Usefulness
MPD is useful in those ways. It would be fine to use MPG if gas and diesel prices were the same, but they are not. And MPD is much better than the EPA's funky, proprietary MPGe used for electric vehicles. It is more straightforward to use a common denominator(dollars) for every type of vehicle. Electric cars don't use gallons of anything, so why use "Miles Per Gallon Equivalent"? Drop a note below if you find this method useful or stupid. Enjoy MPD's!