This type of system would seem to have the same failure modes that complex baggage handling systems have. [1]

They are both moving baggage (passengers) on demand between two points. I seem to remember seeing an article indicating that the failures Denver was having (all the empty pods end up at one spot) was visible in experiment, but I can't find it now.

[1] http://www5.in.tum.de/~huckle/DIABaggage.pdf [2] http://cdn.intechopen.com/pdfs-wm/630.pdf