When I was first referred to this Gawker expose of a certain dillema encountered by NYC subway riders — and the, ahem, “subtle” functions provided by metrocard vending machines to help solve the problem — I thought it was something that only a few deeply disturbed and intense commuters would ever notice, let alone spare the brainpower to try to solve. It turns out, however, that a great many of my friends and colleagues were quite familiar with the issue, and many had already developed their own little schemes and formulae to navigate the loopholes.

I won’t repeat all the details in the excellent and amusing Gawker piece, but the basic gist is that it is possible to find yourself with a metrocard (a subway fare card, for those of you outside NY) with less than a full fare’s value on it. But the card re-filling interface on the vending machine seems restricted to denominations divisible by a single fare (i.e. $2.00), so how is it possible to add an amount to your card that will make up the difference of that extra dollar on the card? This state of affairs is complicated (in fact, it is caused) by the fact that card buyers are awarded a 20% bonus for purchases over $10. All this basically means that, if you want to “gross-up” to a card value that will neatly divide into a series of rides and end up at $0 — while still taking advantage of the bonus amount — you will require at least a Master Degree in mathematics…

One goal of user-centered design is to determine the right visual priority of the various functions offered by a particular interface. Obviously, not every link / tool can be presented with the same degree of prominence and it is always hard to decide which functions should be front and center and which can be relegated to a less obvious placement. The metrocard vending machines make it very easy to add fixed denominations to your card, but the “other amounts” button is easily missed by frequent users whose regular, ingrained interaction routine does not include this function. In other words, it’s the kind of function that you wouldn’t notice unless you needed it, but by the time you realize you need it it’s invisible to you because you have mentally glossed over it for so long.

I certainly don’t appreciate a math-induced headache with my morning commute, but this problem is a great illustration of a an important user-centered design construct and a good thought-starter to get the engines running after a long holiday hiatus.

This entry was posted on Thursday, January 5th, 2006 at 3:48 pm and is filed under Usability, User Interface Design.