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!