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11 July 2008 @ 06:03 pm
mpg vs gpm  
So it's been said that listing our cars as miles per gallon is kind of foolish, since people don't buy a specific number of gallons and then drive until they run out, they pick somewhere to go and drive until they get there. So it makes much more sense to list fuel efficency in gallons per 100 or 1000 miles. In fact in Canada and England cars are rated as litres per kilometers. Now this doesn't sound like much. Just a change of units, some simple math. But I was thinking about the simple math, and yah, it is simple, but it's also very powerful psychologically because people default to thinging about relationships being linear. I made this image to drive my point home. The bottom number is mpg. The top is gallons per 100 miles. And yes, it's approximate.

It was bugging me enough that I needed to post it. I'm not sure what to do with my revolation. But I guess it really struck me that the prius, which is ~50mpg, uses one less gallon per 100 miles than my old saturn, at ~30 mpg and my new car, at about ~25mpg, uses one more per 100 miles. And I know I did this math when thinking about my purchase, but it just hadn't struck home that my "oh, it's just 5mpg" was a whole gallon! Driving to pittsburgh, at $4/gallon, that's $24. On the other hand, that 25mpg I gave up compared to the prius only gets me $48... so...

Anyway, I wanted to share.
Gergzkzkz on July 12th, 2008 12:15 am (UTC)
Are you feeling yourself today? Not one typo in that whole post!
Nice graphic btw.

I thought of another case of this same numerical trick today. "time saved by speeding". People don't really care about miles/hour; what really matters is hours/mile. So when it comes to whether it's worth it to drive 5mph faster it turns out to matter a whole lot more if you're 20mph than if you're goin 50mph.
katybeth on July 12th, 2008 12:58 am (UTC)
Of course, you're more likely to come across stop lights, stop signs, and pedestrians in a 20mph zone than in a 50mph zone, all of which add more to your time than the extra 5mph saves you. And are you more likely to be pulled over for going 5 over in a 20 or in a 50? Sitting by the side of the road awaiting your ticket costs time, too. :)

And I echo the previous comment: Nice graphic.

Edited at 2008-07-12 12:58 am (UTC)
geekosaur on July 12th, 2008 02:52 am (UTC)
actually, there are typoes
still the cat we know and love...
This is a test of the Mugar Omnimax Theatre.dcltdw on July 12th, 2008 04:28 am (UTC)
I was told by my EMS instructor that a study was done on time saved by emergency vehicles responding in an urban situation. Generally, it was no more than 5 minutes -- and this is for calls that originate at a nearby house and then are transported to the hospital, so it's probably not just a few blocks or anything.

Suddenly, speeding looks pretty ridiculous except for very long distances. :)
Podpeople. Benevolent podpeople. That's my theory.vibrantabyss on July 12th, 2008 06:59 pm (UTC)
when i used to regularly drive here from NJ I would tend to *cough* exceed *cough* something or other by about 30, until I got within 30 minutes of the end, at which point it became 'not worth the risk' and i'd drive within normal limits... not that the end bit was any more likely to be patrolled, but....
Jadiajadia on July 12th, 2008 12:48 pm (UTC)
Wow, this is really cool. I never realized this before. Thanks!