Avoiding Affordances: Unusability Engineering

January 21st, 2007 | Category: Essays

With all of the semi-recent focus on usability, I’ve noticed a growing countermovement that doesn’t get near as much attention: unusability. I’m talking here about deliberately designing something so that it’s not usable, not the much-maligned negligence of design that renders things unusable.

“Bum-proof” benchFor example, there are several bus bench designs that allow sitting while waiting for the arrival of mass transit, yet prevent the bench from being used as a bed. Most of these designs involve armrests or ridges in the seat to prevent one from lying prone across the bench, but my favorite is the backless, round-top bench: The seat is shaped like half of a cylinder and allows one to sit (albeit not a luxuriously comfortable place to park yourself). Without your feet on the ground though, you’re not likely to stay on top. Therefore, there’s no napping on this bench. In one of his books on L.A. (City of Quartz, Vintage, 1990), Mike Davis calls them “bum-proof benches.”

The manipulation of the perceived affordances of objects and surfaces is another great example. Donald Norman discusses a few of these in his book Turn Signals are the Facial Expressions of Automobiles (Addison-Wesley, 1992). Chairs and tables offer surfaces that are affordances for the support of weight. That is, a table affords support. If you have a glass counter on which you don’t want anything placed, it should be slanted. If it’s flat, it gives the perception of affording weight placed on top (and often ends up cracked).

The handrails around hotel balconies are typically rounded or beveled in such a way as to prevent the setting down of a beverage. This is to keep one from setting a beer bottle on the rail then drunkenly or excitedly knocking it off onto passers-by, cars, or just the ground below. This is not a design flaw. It is an engineered unusability.

Skate-blocked ledgeIn the past ten years or so architects and urban landscapers have made or retrofitted handrails and ledges to make them unusable for skateboarding. Large knobs welded onto metal handrails or blocks bolted to ledges keep skateboarders from using these surfaces as props or obstacles for their maneuvers. Again, these are not mistakes, but designed — if even often clumsily or not exactly aesthetically — for preventing a certain use.

There are many other examples, but it just struck me that the flipside of usability (in its deliberate form) doesn’t get much attention. Be on the lookout for things designed to prevent their use.

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