If you look at fuel economy in miles-per-gallon, the statement above sounds insane. Look at it in gallons-per-mile, and the societal benefit of improving a guzzler's efficiency outweighs improving a fuel sipper. That means the 2015 Ford F-150 could do more to reduce fuel consumption than the Prius.

This was pointed out to me by economist Michael Madowitz, who counts himself among the ranks of journalists and analysts that repeatedly tell anyone who will listen how fuel-over-distance is a superior measure of economy, while we miss the big picture by stubbornly sticking to miles-per-gallon as the primary basis of consumption comparison.

Madowitz works with the Center for American Progress, a non-partisan think tank. He's also a car guy, and caught our attention tweeting his new ways to think about fuel economy.

The reason he and many others defend a gallons-per-mile system is that while MPG always increases linearly, gallons of gas burned per *x *miles is "far from linear," as Madowitz pointed out.

It's also more practical — most people don't measure their travel by gasoline used, we think in miles covered.

Getting into our example, Madowitz made the case that the rumored "3 MPG" increase in the new F-150 will result in less gas burned than the even a larger increase one would experience buying a Prius over a Corolla.

A 1 MPG increase is not equivalent to a 1 GPM decrease. Increasing the MPG of a vehicle that's already frugal on fuel doesn't reduce gas used over 500 miles by much. Meanwhile, an efficiency increase that's a smaller number in MPG but greater in terms of percentage of the original will reduce GPM substantially.

Imagine you're deciding whether to buy a Prius or a Corolla. The Corolla gets 30 MPG, the Prius gets 49 — 63% more. But if you're driving 500 miles, you only reduce gallons of gas burned by about 6.5 driving the Prius.

Madowitz focuses on two effects in this scenario: First, let's say you're deciding between a used 2013 F-150 that gets 14 MPG to a 2015 one that people are speculating will get 3 MPG better, bringing economy to 17. MPG would increase by 21%, but you burn about 6.3 fewer gallons of gas over 500 miles.

Looking at this chart, you can see the old F-150 vs new F-150's consumption (black) is steep, while the Prius vs Corolla (green) takes up the shallow portion of the curve.

*The blue line is linear MPG and red is the general curve of gallons per x miles, black represents the range the F-150 occupies and green is the difference between the efficiency of a Prius and a Corolla.*

The second effect that comes into play is that many more F-150s are sold than hybrids. According to the data he found, it was about half a million vs 150,000 Prii. Madowitz went on to say it seemed like all hybrid and EV vehicle sales combine only became comparable to F-150 sales last year.

If the efficiency of a small group of vehicles is improved significantly, the total amount of fuel saved will still be less than if the consumption of a massive group of vehicles increases slightly.

For a more direct comparison, the 150,000 people who bought a Prius over a Corolla cut American oil consumption by some 670,000 barrels per year. If Ford hits the 3 MPG increase we heard about when the 2.7 EcoBoost was first being speculated on and F-150 sales remain consistent, US oil consumption would drop somewhere between 1.4 and 2.3 million barrels a year.

*Some estimations are made here, but efficiency is based on EPA data from FuelEconomy.gov, our chart assumes all F150's are automatic 4WD with a 60/40 mix of highway to city driving. Madowitz used approximate sales figures from Edmund's and Autoblog.*

## DISCUSSION

First off, well written Andrew. Second, it was awesome meeting you Saturday night. I hope you enjoy your stay in Detroit.

Madowitz's whole "gallons per mile" idea is basically just asserting that relative increases in fuel economy are more important than absolute increases in fuel economy. It's a pretty basic idea.

The best way to understand it, I think, it to just take the idea out to extremes. Imagine you've got a 1mpg car that gets tuned to now get 2mpg. An increase in 1mpg.

Now imagine you've got a 100000000 mpg car that gets tuned to now get 100000100 mpg. An increase in 100 MILES PER GALLON!

Let's go 50 miles. The first car, before the tune, will use 50 gallons. After the tune: 25. That's 25 gallons saved.

After driving 50 miles, the second car will have used effectively 0 gallons both before and after the tune. ~0 gallons saved.

Madowitz is basically just pointing out that 25 gallons saved is more than 0 gallons saved. Even though the tune gained the second car 100mpg vs. the first car's 1mpg, it's the relative increase in the fuel economy ((1mpg/1mpg) > (100mpg/100000000mpg)) that provides insight into fuel savings.