Elevators: How do they control dispatching?

In my experience, I’ve noticed the following: in some buildings, when you press the elevator call button, an elevator will come very quickly, and likely be empty; while in other buildings you have to wait a long time and the elevator will be packed. This leads me to suspect that in the first case, when you press the button, the system will send any available idle elevator directly to your floor, even if another elevator is going in your direction and is about to pass your floor. In the second case, I’m assuming that you are being forced to wait until an elevator, already moving in your direction and due to pass your floor, reaches you. I can see that this would be more efficient energywise.

My question is, how do they set this? Is there a control panel in the utility room of the building? Or do they have to call the elevator company to come in and adjust the wiring?

The elevators are controlled by a computer in the building, which decides where to send each one based upon demand and proximity. Remember that the computer has to consider not only the people calling for a car, but the people inside each car and where they’re going. Some are more efficient than others. Some buildings simply do not have enough elevators for the amount of people they have, leading to delays. Elevators typically default to the ground floor when not in demand, and the computers may shut some of them down during off-peak times and at night to save power, meaning you may have to wait longer.


Elevators can be programmed just like anything else with a chipset, and are set in accordance with the wishes of whomever owns or occupies the building. For good reason, the controls are only accessible to a certified elevator mechanic, and generally reside in a dedicated elevator control room.

D’oh! Simulpost!

Controlling elevator allocation is a tricky tricky thing. It’s easy to invent a simple controller, but for buildings with many floors, especially office buildings where users exhibit non-random behaviours (mostly up in the mornings, mostly down at evenings) it gets complicated. I think it’s one of the few areas in algorithms the layman can grasp the basics of. (Or at least gripe about them. ;))

See such pages as this and this, or search for “elevator scheduling algorithms” to find out more.

Fur further exploration: Maxis’ “SimTower” game is really more an elevator control simulator than just a game.

The game lets you adjust parameters such as where a given elevator waits, skipping floors, at what number of passengers it will change to an express, etc.

As for the real ones, I did a little digging around otis.com, and found they have fuzzy logic systems and controllers that calculate which elevator to send to which floor based on 20+ parameters.

Wow! Thanks for the responses. I didn’t realize, though I should have, that this type of research has been done on the subject.

Not only has this type of research been done, but there is a degree of overlap between elevator scheduling algorythms and where a computer’s hard drive keeps it’s read/write heads and the optimal order for processing drive access requests. Requests from different locations, taking care of them in a quick order while not unduly starving any particular request, fixed time to travel from point A to point B, etc.


The elevators where I work use fuzzy logic that’s extremely fuzzy.

Meaning, you get on, hit the button for the floor you want, and, if the button even lights up, the elevator sometimes heads in the other direction, stopping on random floors, if at all.

One time, I was going from the 5th floor to the 3rd. The elevator started by heading up a few floors, then changed directions (without stopping on any floor) and went down to 3.

Most people blame traffic when they are late for work; we get to blame the elevators!