AN ARMCHAIR VIEW OF ESCALATORS
Roger W. Garrison See also "Escalating
Confusion" by Robert P. Murphy
There is much pedagogical value in applying the economist's standard
analytical tools to issues about which students have a common-sense understanding.
By demonstrating this point repeatedly, Steven Landsburg has become the
profession's pre-eminent
The relevant decision, undoubtedly made subconsciously by the typical
stair climber or escalator rider, involves a trade-off between "resting"
and "moving." These two gerunds, then, label the vertical axis (resting)
and the horizontal axis (moving) of the indifference-curve map in Figure
1. The ultimate form of resting in this context consists of standing still,
which is the level of rest that defines the vertical intercept of a linear
budget constraint. (A possible budget-constraint non-linearity in the case
of moving walkways will be considered below.) The horizontal intercept
corresponds to zero rest and has our stair climber racing as fast as possible.
We should let this budget constraint be applicable only to ascending the
stairs; the constraint applicable to descending would have a horizontal
intercept lying further to the right. People can race down the stairs faster
than they can race up them.
Figure 3 is identical to Figure 1 in terms of the shape and location
of the budget constraints, but it differs from the earlier figure in terms
of the preference map. Given the particular indifference curves of Figure
3, we get a tangency solution in which the rider actually leverages the
gain provided by the escalator. As implied by a movement from Point 1 to
Point 2, he runs up it, though with stairs he would only have walked up.
We can easily imagine the circumstances in which these preferences are
understandable. Suppose it is very much worth while to get to the next
floor quickly but that if you can't get there quickly, it doesn't much
matter whether you get there a little later or even later still. Train
stations and airports provide circumstances where these indifference curves
might apply.
An indifference-curve
treatment of moving walkways would seem to be similar in all respects to
our treatment of escalators. But there are critical differences. The budget
constraint has a much shallower slope and possibly is non-linear near the
vertical intercept, virtually precluding the kind of dominant corner solution
that characterizes our analysis of escalators. Figure 4 shows indifference
curves from the same preference map used in Figure 1. But the budget constraint
has a slope that is considerably less than in Figure 1: On a level playing
field, people can trade rest for speed on much more favorable terms.
Using indifference curve analysis to show why people stand still on
escalators but walk on moving walkways helps establish the near-universal
applicability of economic theory. Working with contrasting preference maps
(such as those in Figures 1 and 3) to deal with an issue where the student's
own intuition is fully in play may help the student to read indifference
curves in less intuitive cases. And challenging the students to apply basic
economic tools to similarly frivolous issues can result in fun and even
learning.
Landsburg, S. E. (2002). Everyday Economics: "Why do you
walk up staircases but not up escalators? Landsburg, S. E. (1993).
1. One of my colleagues whose armchair is much newer than my own claims that she can go up the stairs (taking three steps at a time) faster than she can go down (having to use every step). 2. Actually polling the manufactures
of escalators on this question, of course, would violate the spirit of
armchair theorizing. In any case, we can claim they 3. According to Landsburg (2002), the
Bils-Landsburg argument "proves...that even if you choose to walk on the
escalator, you should |