Poka-Yoke at the Gas Station

written by Justin Davis on December 30, 2013

A poka-yoke device is a way of designing an interface or system to be naturally error-proof, put together in such a way that a user can’t make an error. It’s a type of usability enhancement that makes systems more efficient and less error-prone. Developed by Toyota in the 1960′s, this terms has been applied to the lean manufacturing space for some time, now making its way into other industries, the web included.

The cool thing about poka-yoke devices is their inane simplicity. These design choices are so seemingly obvious that most users don’t even notice them, instead, just completing their tasks as they should. Take for example, my experience at the gas station just this morning.

The gas and diesel spouts are different sizes, to prevent someone from accidentally using diesel in their gasoline vehicle. Perfect poka-yoke.I stopped at the gas station to fill up my car, which takes regular ol’ unleaded fuel. As I was standing there getting ready to fill up, I grabbed the green, diesel fuel handle by mistake (hadn’t had the full cup of coffee yet). As I went to put the spout into my gas tank, the problem was immediately apparent: it didn’t fit!

This is a great example of poka-yoke at work. Instead of allowing me to make the mistake of filling up the car with diesel fuel, the designers of the pump stopped the error from happening completely, by making the spout on the diesel pump too large to fit in an unleaded tank’s fill spout. Seemingly obvious, and obviously brilliant. (It’s worth noting, however, that this¬†wouldn’t work in reverse, as the smaller gas spout would fit in a diesel tank. Making one square and the other round would create a two-way poka-yoke device.)

Poka-yoke concepts can be used on the web just as they’re used in manufacturing and physical environments. Using dropdowns instead of textfields when the user needs to enter something from a fixed set of options is a great example. Because the user can’t type in their own value, the input field prevents an error from happening straight away. Likewise, disabling a submit button until all required fields have been entered is also a poka-yoke device – a user is unable to make the mistake of submitting the field while lacking data.

If you’re looking to make the usability on your site better, looking for poka-yoke opportunities is a great way to do it. They’re usually small improvements, but can have drastic effects on the ability for people to get through your interface.

What other poka-yoke devices have you seen, both on and off the web? How are you using them to prevent errors in your design? Leave your thoughts in the comments!

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