I've read it once was the busiest rail junction in the US and perhaps the world, and maybe it still is in the US: the Chicago Transit Authority elevated junction at Lake and Wells Streets. All trains on the elevated structure entering or leaving the Loop must pass through this junction. There are 5 L lines sharing the tracks: Green, Pink, Brown, Orange, and Purple. The first 4 lines have at least 100 trains/weekday while the Purple line has maybe 40/day. The Pink, Brown, and Purple line trains pass through twice on each trip, entering the Loop, going around and exiting, so they visit the junction twice within about 10 minutes. The Green line trains go through once in each direction, and the Orange line passes through once on its route to/from Midway Airport. So, by my reckoning there would be >= 200 Green line trains + >= 200 Brown line movements + >= 100 Orange line trains + >= 200 Pink line movements + >= 80 Purple line movements through that junction every weekday for a grand total of at least 780 train movements per weekday. No too shabby!
"Welcome aboard Orange Line run 711. Travel time to downtown is 25 minutes. Next stop will be Pulaski."