Fascinating Human Behavior

Miles per Gallon across different speeds. (Actual data)

Miles per Gallon	at 75 MPH	at 65 MPH	at 55 MPH
Car 1	30.7	33.5	39.9
Car 2	36.5	44.8	51.9
Car 3	17.8	21.2	23.8
Car 4	25.9	29.3	34.6

It is clear that Car 2 is the most fuel efficient car.  Obviously when you drop from 75  MPH to 55 MPH you improve your miles per gallon.  If all four cars drive 10000 miles, which car will save the most gas by reducing the speed from 75 MPH to 55MPH?

Reducing to 55 from 75 MPH	MPG Improvement
Car 1	9.2
Car 2	15.4
Car 3	6
Car 4	8.7

This question is complex.  In situations like this, rather than do the math our brains look for an easy relationship to use as the basis for the decision.  We substitute something that looks like the same question and use that answer as the answer to the more difficult question.  In this case we are drawn to the MPG change as a stand-in for doing the more difficult calculation.   On that basis, Car 2 is the answer.  

But that turns out to be wrong.  Car 2 will save just over 81 gallons of gas per 10,000 miles driven.  But Car 3 will save over 141 gallons of gas for the same distance.  Only Car 1 saves less gas that Car 2.

Human behavior is very interesting.  As an experiment next time you're on the highway. Drive at say 10% over the posted speed limit (you’d better be in the right lane)  Then count the number of hybrids that pass you.  Assuming that many people who buy hybrids do so because they are “environmentally conscious”, you have to wonder why they don’t drive close the the speed limit where their gas consumption will be lower.  The answer is that we are all comfortable with a certain level of hypocrisy, (except for that lone wolf driving at 55 in the right lane that you nearly rear-ended!)


The issue of framing and looking for an easier problem to solve is covered well in Daniel Kahneman's new book Thinking Fast and Slow.