How do elevators decide where to go?
A lift keeps going while someone needs it in that direction, then turns around. Most of the rest is built on that one rule.
Most lifts follow one rule: keep going while someone ahead needs you, then turn around. On the way up a lift stops for people getting off and for people waiting to go up. When nobody is left above it, it heads down and does the same.
Serving calls in the order they come in would be worse. A lift that runs from the first caller on 2 to the next one on 9 and back again spends most of the day empty.
A few other things happen on top of that:
- A full lift skips people waiting, since nobody could get in anyway.
- With several lifts, the building picks one car for each call. That is the lamp you see light up over one door.
- In the morning, empty lifts go back to the lobby. In the evening they wait higher up.
- Tall towers split floors into zones, with express lifts that skip the lower ones.
If you want to try writing these rules yourself, that is what Elevator is about.