The biggest part of an elevator ride is the opening and closing of doors. So the solution actually would be to get people within 1-2 floors of their destination.

So if you walk in and someone already selected floor 20 and you want to go to 21, you aren't able to select 21. You have to get off at 20.

Same thing to get in. If someone already called an elevator to 1 floor from you, you can't call it for your floor.

Give people with mobility issues a Key that overrides this.