Saturday, July 26, 2008

Converting miles per gallon to cups per mile

Though I do love Paul's more philosophical posts I thought I'd change things up a little by responding to this post on one of the NYTimes blogs:

“Miles per gallon is misleading and can play tricks on our intuitions,” Prof. Soll said in a press release, which also links to an interactive quiz.

Profs. Soll and Larrick offered an alternative metric: gallons per mile. Expressed in gallons used per 100 miles, 18 m.p.g. becomes 5.5 gallons per 100 miles, and 28 m.p.g. becomes 3.6 gallons per 100 miles. And the difference is suddenly obvious: nearly two gallons every 100 miles, or a difference of more than $8.

I thought that it'd be interesting to measure gas volume more directly. Instead of using 100 miles, just use one mile and use the appropriate household measurement.

Table of US Cups of Gas used per Mile traveled

MpgUS Cups per MileExample car
10mpg1.6 Cups per MileBentley Azure Convertible
15mpg1 Cups per MileJeep Grand Cherokee
20mpg.8 Cups per MileToyota Tacoma
25mpg.6 Cups per MileModel T
30mpg.53 Cups per MileToyota Corolla
35mpg.45 Cups per MileVolkswagen Jetta
40mpg.4 Cups per MileHonda Civic Hybrid
45mpg.33 Cups per MileToyota Prius

I just threw this together pretty quickly so please forgive me if I rounded a little or compared cars across different years and features.

As you can see, the savings really happen on the far end with people switching from gas guzzlers to slightly more fuel efficient cars. Getting hippies like me to buy priuses surely doesn't hurt but it's not the main solution.


Bret said...

The problem with renewables hasn't really been demand (except in primitive economies where externalities are not valuated), since I'm not even sure when. The problem is production. I have no idea how many press releases I've seen in the last two weeks about this or that Plug-In Hybrid startup. It'd be an exciting time to be an automotive engineer, for sure.

Tommaso Sciortino said...

I don't know what you mean by that. The "problem" of production was solved by increasing demand so much that people offered so much money for hybrids that producing them started to sound really good. Otherwise there's be no reason to make them.

In conclusion, we need a carbon tax.

Bret said...

I don't think that 'demand' for renewables is so much the consequence of Joe Consumer deciding maybe gas is too expensive as it is the consequence of an overriding international concern about sustainability and global warming.

That being the case, the operative question is not 'What is the exaaact optimal number of Priuses to produce next year?' But rather, 'How do we get as much renewable/free energy into our economy as possible?'

As I've admitted many times, free markets are not as good at answering that second question as they are the first.

Tommaso Sciortino said...

Ok, clearly you're right. The research in renewables is clearly more than would be warranted just by the increase in gas prices. Clearly a concern for the environment is key. But the causal mechanism is that car makers suspect that governments are going to respond to these environmental concerns by using regulatory apparatus like carbon taxes to goose demand. As indeed many countries already have.

I guess we're not really disagreeing.