I have never used one, in fact only became aware of twin elevators this week from the recent EconTalk episode with Tim Harford. I'm wondering as a user of a t

I have never used one, in fact only became aware of twin elevators this week from the recent EconTalk episode with Tim Harford. I'm wondering as a user of a twin elevator, how are you even aware that the elevator below is preventing you from descending? The only situation that I can think of where this would happen is if both elevators are taking passengers down to the ground floor and the higher elevator either has to wait for the lower one to fill or empty. Does this result in a noticeable delay? Do you notice that on average delays are actually lower compared to normal single elevators?