Usability case study: The NYC subway turnstiles

This week I went out for an observational study about the interaction between people and the NYC subway turnstiles.

NYU subway turnstile
NYU subway turnstile

The study was made on two busy subway stations: Bedford Avenue station in Brooklyn, and Union Square station in Manhattan. The observations, and the conclusions, were similar on both stations. Therefore, I will specify my findings in an unanimous form.


  1. A few meters before they get to the turnstiles, people reach to their pockets, wallets, or bags to get a paper card, shaped as a credit card. One face of the card is painted in yellow, and the other one is painted white.
    It is very unusual to see people get to the machine empty handed.

    Getting the cards in advance
    Getting the cards in advance
  2. People swipe the card on the right side of the machine.

    Swiping the metro cards
    Swiping the metro cards
  3. Usually, a ‘click’ sound is heard after the swipe, and the ‘swiper’ moves across the gate to enter the subway platform.
  4. Occasionally, a ‘beep’ sound was heard after people swiped their cards. After the ‘beep’, people were seen swiping their cards again. This scenario repeats itself until the ‘click’ sound was heard, after which, the swiper entered the platform.
    A closer look shows an ‘error’ message on the small display, placed just above the card swiping deck.

  5. On rare occasions, the swiper was swiping the card, a ‘beep’ sound was heard, and the swiper seemed angry.
    This situation made other people, who were lined-up behind the swiper, angry as well. A few of the waiting people were trying to move to another turnstile line.
    The swiper turned back, and went to the ‘refill machine’. After doing so, the swiper repeated the steps from step 2.
  6. The turnstile was used, by different people, both for entering the platform, and exiting from it.
    On many occasions, people were trying to exit the platform from a turnstile that was occupied by other people, who where trying to enter the platform.
    Ofter 1-2 second of confusion, the ‘exitter’ (it was never the one who enters) was turning to another turnstile to exit the platform. Some of the exitters took the liberty of exitting the platform from the emergency exit, which was open at all times.

    Commuters go in and out the platform through the turnstile, or through the emergency exit door
    Commuters go in and out the platform through the turnstile, or through the emergency exit door

Major insights

  1. The NYC subway turnstile is a very understandable device. Whether it is because people tend to use it often, of because its design is very simple, people rarely get confused while using it.
  2. At first sight, it felt like the the fact that people use the same turnstile to enter and to exit the platform indicates a design flaw, that might become a major one on rush hours. A longer observation on the turnstiles reveal that people tend to work-around this limitation pretty easily, while spending about a second or two doing so.
  3. Since there is no indication on the card for the amount of funds attached to it, people tend to block the turnstile on cases of ‘insufficient funds’, and to repeat previous steps in the interaction.


Be careful of over-engineering – Intuitively, I was surprised that the engineers, who designed the turnstile, were not concerned by the fact that people would have to cross the turnstile from both of its sides at the same time (to enter and to exit the platform). I assumed that a better design was one that allowed entering and exiting the platform from different locations.
But engineering and design are all about decision making, and compromises. The design I thought about is one that requires more space, and eventually less effective. Apparently, people do not care that much about this ‘limitation’, and address it very easily.
There might be an optimal design that could solve this situation, but sometimes, looking for complex solutions for simple situation is just over-engineering.

An indication for the amount of funds on the cards could be helpful – Since people tend to hold their subway (metro) cards a few steps before they reach the turnstile, having an indication for the amount of funds on the card could save time and frustration when addressing a situation of ‘insufficient funds’.
Also, it could have been useful if people were able to fill their cards with ‘rides’, instead of plain money. For example, one would be able to fill a card with 1-10 rides, instead of $20-$60. This situation could make it easier for people to track and remember the number of rides they still have in their credit (currently, the cost per ride is $2.75, which make it relatively hard to calculate the number of rides in $20, and supposably leads to ignorance).
Here are few suggestions for such indications on the NYC metro card:
Suggestion for NYC metro card design

Simple switch circuit

To gain better understanding of electronic circuits, I built a simple LED circuit.

LED circuit
LED circuit

Later, I added a force-sensing resistor. I used the resistor manually as a switch to close the circuit.


Closing a LED circuit with a force-sensing resistor
Closing a LED circuit with a force-sensing resistor

One thing if very clear to me know — whether it will go through some dead LEDs, or through a few burned down dc engines, I learn better when I try things hands one. Since I started to use the digital multimeter, I was able to test my understanding of circuits on live working components, but more importantly, I started to feel more confident about my knowledge. Can’t wait to build a more challenging piece.

Physical Interaction: Interpretation and Thoughts

What is physical interaction?

Interaction: a cyclic process

In order to answer this question, I believe that I should first describe what is an interaction? According to Chris Crawford (“The Art of Interactive Design: A Euphonious and Illuminating Guide to Building Successful Software”, 2003), an interaction is:

“a cyclic process in which two actors alternately listen, think, and speak.”

Crawford claims that interactivity must be cyclic, and that it must includes a process of listening, thinking, and speaking. But what if an interaction includes only a single cycle of a question and an answer? What if the one actor doesn’t listen, and instead says something that is unrelated? What is the unrelated reply makes the first actor go for another cycle (to process what he/she heard, and to say another thing in reply)? Would that be considered an interaction?

Number of cycles: an interactivity strength scale

Crawford mentions that, to his perspective, there are degrees of interactivity. Therefore, interactions could be strong or weak, based on the level of listeningthinking, and speaking by those who participate in the interaction.

To add to Crawford’s degrees of interactivity model, I would say that since an interaction is cyclic process, the number of cycles could be used as a measurement for the strength of an interaction, and that minimum strength of an interaction is a single cycle.

I agree with Crawford’s determination that in cases where the occurrence does not lead to (at least) a single full cycle of interactivity, this occurrence would be considered as a case of cause and reaction.

For example, when two people engage in a long conversation about the theory of Repeated Games With Incomplete Information, they experience an interaction that requires many cycles of questions and answers, that lead to many other repeated cycles. This conversation would be considered as a very strong interaction.
In contrast, when two people stand in an elevator and greet each other with ‘good morning’, I would say that, even though their interaction went through a single cycle (or a single exchange), this single cycle satisfies the minimum requirement for an interaction. Obviously, the strength of this interaction is very weak (some would say that this is the weakest interaction possible, but I always consider an interaction between people as one that includes an exchange of information the surpass the the words that are being said vocally).

In case where one of the actors greets the second actor with ‘good morning’, and the second actor embraces the greeting, but do not reply, I would consider that a case of cause and reaction.

Interaction: an exchange of information

I would also add that an interaction must be a cyclic process in which actors listen, think, speak, and exchange valuable information. Information is valuable for an interaction in case where it was related to the previous cycle, and had an effect on the next on.

For example, let’s have a look at the following conversation:

John: “What is the time now?”
Dana: “The leaves are falling because winter is coming.”

If John considers Dana’s answer as unrelated to his questions, he might stop the conversation, and won’t say anything else. John might as well assume that Dana did not reply to his question, and did not even talk directly to him. In this case, I would argue that Dana did not interact with John, and therefore, there is not even a single cycle of interaction, meaning that there was no interactivity at all.

This situation is very similar to the highly frustrated experience of operating a computer, and getting a repeated error message that doesn’t seem to have any connection to the operation, and that doesn’t lead the user towards his next step.

Error code. [taken from]
Error code.
[taken from]

What if John asks his question again, assuming that Dana miss heard him? What if after Dana’s reply John forgets about the time and starts to gaze at the falling leaves? Similarly to the previous case, In this one I would say that both actors are reacting to one another, but do not perform any real interaction between them.

But what if, somehow, John understands what is the time (or at least he thinks he understands) from Dana’s answer?  In this case, even though the content of the conversation doesn’t seem to be of any value, I would consider it an interaction, since Dana’s reply was valuable to complete a single cycle. In other words, regardless to Dana’s reply content, if this reply pushed John to try to re-interact with Dana, Dana’s reply effected the next step in the interaction. And therefore, it was valuable.

To summarize it all, I would argue that an interaction is:

at least a single exchange of valuable information that leads to a cyclic process in which two actors alternately listen, think, and speak.

Physical interaction

In my opinion, a physical interaction is one that includes a physical object, and that the physical object plays a major role in it. I would consider a physical object anything that has a tangible attribute. Therefore, humans, for example, are physical objects. This conclusion led me to a disagreement with Bret Victor’s article about the future of interaction design. Even though the future, as presented on Microsoft’s concept video, does not fulfil the potential of physical interaction, humans are playing a major role in it.

Physical interaction with digital interfaces. [taken from]
Physical interaction with digital interfaces.
[taken from]

For example, an exchange of information between two servers would not be considered to be a physical interaction. But in my opinion, any interaction between human and a machine is a physical interaction.

We can say that a physical interaction is

a cyclic process, on which a physical object plays a major role, and includes at least a single exchange of valuable information.

What makes for good physical interaction?

By now, it is clear to me that a good physical interaction must include a good use of physical object. By saying ‘good use’ I mean that it should be clear that the interaction could not be as strong, or even could not occur at all, without the physical object.

Having said that, and without quoting Don Norman’s book The Design of Everyday Things, I would say that a good physical interaction would also be one that fulfils its potential in the following ways:

It is sensitive

Remember the times when you got a new shirt, or a new haircut, and no one told you anything about it, as if it wasn’t happening? Have you ever experienced a situation where someone important to you forgot about an important day for you?

Computers have the potential to impact our lives with just a minimal effort. Think about a scenario where your desktop lamp would change its tone of light according to your mood, if it is saying that it feels you. Wouldn’t that be nice? What if your home stereo would lower its volume, or just lower its treble sound when you have a headache? What if your refrigerators would pour a glass of water when its sensors hear you coughing?

It is surprisingly smart, but not arrogant

In continue to the previous topic, a good (physical) interaction is one that has a sense of surprise in it. Repeating the same interaction over and over would probably kill this effect, and therefore, a good interaction should be one that evolves, and gets smarter in time.

The best interactions would be those that does not leave the user with a feeling of “that was great, but I have no idea what happened.”. I cannot stand looking at my father as he admires new features on his phone, while secretly admits that he is no way near the understanding of this features, and how they actually work. This interaction leaves my father (and many others) with the feeling that he cannot play a major part in the new world of computer based interactions. In other words, although my father appreciate these interactions, they tend to leave him with some frustration, which leads me to the next topic –

It is satisfying

Rolling back to the earlier parts of this post, I can say that a strong interaction, one that includes many cycles, is surely satisfying. But the feeling of satisfaction could be achieved even on weak interactions, and should not be overlooked. A satisfying interaction would lead a user to be more engaged in it, and would push the user to explore new ones.