Turnstile Trouble

You can always tell an out-of-towner in New York’s subway. He’s the
person that has to swipe his card five or six times through the
turnstile, jamming the whole weight of his body against the
immovable bar, until it finally works.

Real New Yorkers take pride in operating the turnstile as smoothly as
possible. They learn through bitter experience at exactly what pace
the card must be swiped, and manage to do the
walk-up-swipe-and-walk-through maneuver in one smooth, yoga-esque
motion. And just when you’ve really got the hang of it, your
metrocard is expired, and there you go slamming your body against the
bar, embarrassed to look like you’re from out of town.

Slit, Not Slot

A little while back, I wrote about <a href=”http://pinds.com/articles/2001/04/04/metrocard-mess”
title=”MetroCard Mess”>how frustrating
the Metrocard vending machines are. But the fun doesn’t stop
there. The turnstiles in the subway in New York have several usability
problems.

The main problem is the fact that they use a slit that you must
swipe your card through. Other subways, in contrast, has a slot
that takes the whole card inside the machine, so that it can suck it
through the system at its own pace, thus eliminating a whole category
of errors. In New York, it’s up to the user, not the machine, to
ensure that the card is swiped at the right speed. And it’s up the
user to ensure that, when aiming for the slit, he doesn’t dip the card
too late, or pull it up too soon.

Please Swipe Again at This Turnstile

This problematic design also leads to more subtle errors,
which, in turn, is the reason behind the infamous “Please swipe card
again at this turnstile” message. With a single-ride metrocard, for
example, the machine must first read the available balance on the
card, determine whether that’s enough, then deduct the $1.50 fare, and
write that new amount back on the card, all within that single swiping
motion by the user.

If, for some reason, the user pulls out the card too soon, it might
get interrupted before writing the new amount back, or even
while writing the new amount back. In order to deal with this
problem, the turnstile has to remember what card it just saw, so that
when you swipe your card again, it can finish the transaction it was
doing, rather than start a new transaction.

Of course, people frequently ignore this message, and assume that it’s
the turnstile that’s broken, so they move to another turnstile and try
again. So the MTA has to put up posters, explaining to people that
it’s important that they stick to the same turnstile. All in all,
both the turnstile and the user must do a whole lot of
work to make up for the fact that the design doesn’t guarantee
that the transaction is atomic.

Did It Go Through? Ouch! I Guess Not!

All of this is augmented by inadequate feedback. As mentioned, people
have taught themselves this smooth walk-and-swipe
motion. Unfortunately, this means that, by the time you’ve swiped your
card, your body is already so far ahead that you can’t read the
display that tells you that you failed.

There is an audible feedback: A beep that I believe actually is
different when you’re okay and when you’re not. But the difference is
too hard to notice. There’s also the clicking sound when the bar is
released, so it’ll turn when you lean against it. The
absence of this clicking sound will also help tell you that
you’ve failed. But the timing here is tricky, since it’ll take a
while before you realize that the sound is not just delayed a bit,
it’s actually not planning on coming at all.

In any event, I usually end up unconsciously sensing that
something’s wrong, but by the time this realization reaches my
conscious mind, it’s too late. I have too much inertia to stop
moving, and a split-second later, I jam my body against the bar,
embarrassed look up and around, hoping that nobody noticed.

What aggravates the pain is that, while probably about 95% of my
swipes are successful, when I have to swipe again because of a
failure, it usually takes three or four more tries before I succeed. I
believe this is because the swipe is an unconscious bodily skill.
When there’s a breakdown, and I become conscious about swiping, I
can’t do it right. This is a common phenomenon: Try to breathe
normally while consciously monitoring your breath, and you’ll know
what I’m talking about.

The English Boarding School Effect

At first, I actually liked this interaction style. When done right,
the elegancy, ease and speed with which you can pass through the
turnstile is, ahhh, gratifying. And, having a technical
background, I was impressed with the technical achievement of
conducting that whole transaction is one swipe, as well as with the
amount of thought they’d put into recovering from failures.

Also important, I enjoyed showing off my mastery of the
turnstiles when I was accompanying visitors. I could clearly
demonstrate that I had truly become a New Yorker.

But later, I came to realize that New York’s subway doesn’t have to be
like an English boarding school. There’s no need to unduly harass the
newly arrived, who are already adequately intimidated by the city
itself. And I also started noticing the frustration and embarrassment
in the faces of especially native New Yorkers, when they occasionally
fail to swipe correctly. This is wrong. Technology should not make
people feel stupid.

Lessons for Design

A few lessons can be learned from the turnstile design:

Design with a clear goal

If the goal is to penalize newcomers and reward regulars most of
the time, then the design can be considered a success. But this is
not a good design goal. It should be easily accessible for both
newcomers and regulars, and in any event, it shouldn’t make any of
these feel stupid.

Eliminate the causes of error

When the turnstile programmers realized that they were spending so
much effort trying to recover from aborted transactions, maybe
they should’ve considered changing the interaction style to
eliminate this whole class of errors.

Give the right feedback at the right time

The audible feedback should more clearly distinguish between
success and failure, and the visible feedback should be moved
further back, past the bar, so the chance of seeing it while
you’re moving forward is increased. Normally, the absence of sound
is a good way of signaling error, because it avoids telling the
bystanders that you’ve made a bummer, but since the interaction
here happens so fast, by the time you realize that the sound is
missing, it’s too late. If the sound could be designed so it’s
directed towards the person in the turnstile, so bystanders can’t
easily hear it, that would help avoid some of the embarrassment of
failure.

Usability test in realistic settings

The turnstiles must be tested both with novices and with people
that have had a lot of time to practice, and be tested by people
moving through the turnstile fast. At this point, it would be
prohibitively expensive to replace all the turnstiles, but at
least new replacement turnstiles could be designed better. The
upside of the massive installed base is that it’s easy to gather
test data: Just mount a couple video cameras at selected subway
stations and analyze the many failures.

Good luck, MTA!