Forcing Functions

Post by Steven Dale

We all do stupid things. Constantly. Wouldn’t it be nice to have something that prevents those things?

Forcing Functions are a principle of industrial and interactive design that shapes human behavior in order to prevent error when using a machine, interface or system. They are functions that – quite literally – force us to behave in a particular way. Forcing Functions are often irritating and annoying but when designed properly, they prevent behaviors that are even more inconvenient and irritating:

  • The reverse key lock in cars. Before the advent of the key lock fob, cars could not be locked from the inside. Was it inconvenient to have to lock the car manually from the outside? Yes. Did it prevent thousands of people from locking their keys inside their cars? Also yes.
  • Placing your alarm clock out of reach of your bed. Yes, when the alarm goes off you have to get out of bed to turn it off. Really irritating, especially on a cold winter’s morning. But more irritating is when you slap the alarm off half asleep and miss your 8 am conference call.
  • Keycard activated lights in hotel rooms. Lights will only be engaged once you insert your hotel keycard in the appropriate slot. Prevents people from forgetting their card and from leaving lights on. A great example of a Forcing Function that benefits the service provider rather than the user.
  • Child proof medicine bottles. One of the most benign and irritating Forcing Functions ever developed. But the display of strength and ingenuity needed to open these bottles prevents children from accidentally ingesting medicine they shouldn’t.
  • Freezing your credit card in ice. A classic from the debt-reduction self-help world that is rarely if ever seen as a Forcing Function. The time it takes to return home from the store and thaw out the credit card provides room to pause and contemplate, preventing poorly thought out impulse purchases.
  • Repeated requests for confirmation of a computer-related action. 99 out of every 100 times you know you want to delete the file you just asked the computer to delete. So why then does your computer keep asking you if you’re sure? Because there’s always that one time out of every 100 when you’re not sure.

Forcing Functions are all around and often completely invisible to us. And yet they seem noticeably absent from our existing transit systems and technologies. I can think of at least half a dozen problems with public transit that could easily be resolved with the proper Forcing Functions:

  • People who do not exit by the rear doors of transit vehicles.
  • Riders who dangerously rush down stairs and platforms to “catch” a departing vehicle.
  • People who refuse to let people off of a vehicle before they board.
  • Drivers who take unapproved breaks.
  • Not having the “exact change.”
  • Riders who will not move to the ends of a subway platform or to the back of the bus.
  • People on escalators who clog both the “walk” lane and the “stand” lane.
  • Chronically behind-of or ahead-of schedule vehicles.

As I see it, our current transit systems are not designed to recognize how people behave in reality. They are instead designed under the assumption that people are purely rational decision-makers that will behave as they are supposed to. We know, of course, that this just isn’t the case.

I suspect there’s something in the human condition that doesn’t like the concept of Forcing Functions because it implies that we are fallible and capable of moronic errors in judgement. We don’t like to think of ourselves as stupid and therefore don’t like the idea of a system forced upon us to correct for our stupidity. No one likes to be reminded of their shortcomings, after all.

Problem is we are stupid. Each and every one of us. And there’s nothing wrong with that, so long as our stupid decisions don’t ripple through an entire system to the inconvenience and hassle of thousands. Why not just admit that, design around it and move on with our lives?

Ironically, admitting to our own stupidity might just be the smartest thing we could ever do.

Beyond those listed above, what other public transit problems can you think of that come down to simple, stupid human error? Name a few and try to suggest a simple Forcing Function that could correct for it.

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