I had a chance to visit 7 World Trade Center today, the newest office high rise to open in New York.

Instead of having up and down buttons outside the elevators, there’s a numeric keypad, where you key in the floor number you’re going to. Then an LED display tells you which elevator to wait for. Once you get in the elevator, you don’t have to press any buttons (and there are none to press).

This is more efficient than the old system, in which two people who were going to the same floor might have taken separate elevators, adding an unnecessary trip. Presumably, during the early morning rush, it is able to clump people going to nearby floors into the same elevator, thus getting more people to their destinations faster by intelligently optimizing elevator schedules on-the-fly, instead of letting any arbitrary person force any arbitrary elevator to take them to any arbitrary floor.

Can you guess the usability bug?

(select this paragraph for the answer:) People who aren’t used to the new system come into the lobby and see an elevator with an open door. They jump into it, and then get stuck going to some random floor because they can’t key in their destination once they’re inside. (end)

In that old Jack Lemmon / Shirley MacLaine movie The Apartment, a 1950’s-era accounting firm accomplishes the same trick by putting human operators (“elevator girls”) in each and every elevator, and having a human traffic director in the lobby direct people to the elevator that will go to their floor.