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IDK if they still do it but Chicago used to run "A" and "B" trains that would only stop every other stop. At some stations, all trains would stop so you could get off and transfer to the alternate train if you needed to.

So basically any given train was only stopping at maybe 60% of the stations.

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I knew some buildings that had elevators that worked that way: one for even floors, one for uneven ones. I always wondered if this really paid off. I guess in a building you almost always are either going to or coming from the ground floor, and you never need to switch elevator. But on a train line you might want to get off at any stop so ~50% of people will need to switch.

I was curious about this too, so I decided to simulate it. It's a fun problem to model and code, with some entertaining places to trip up - for example, that brief awkward period where the elevator is full, but newly arriving people recognize they should not press the button until it leaves. In any case, the answer varies based on the rate of arrival - in some regions of the parameter space it's better if all elevators stop everywhere (intuitively, if odd people arrive every 2 min and it takes 3 min to go up and down, it becomes too expensive to have to wait for the odd elevator). But even in cases where interleaved floors performs better than all floors, there's a solution which is even better there - lower half of the floors on one elevator and the upper half (plus ground floor) on the other. This will make for a fun interactive notebook.

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