I'm sure this question has been asked before, and sorry if it seems dumb, but after Broad St, where do the J & Z go? Into a seperate tunnell? Specifically during rush hour when the M terminates at Bay Pkwy? Do they go onto seperate tracks to allow to the M to run freely on both sides?

J&Z trains go into a tunnel that goes just above the North and
south bound tracks that go into the montage tunnel.


M trains use the middle track just after Bay Pk'way or the CI yard lead tracks at Bay 50th St.

Just south of the Broad Street station platforms, the two tracks become 4 tracks, an inner set of 2 tracks, and an outer set of 2 tracks.

The outer set of tracks (2 tracks) lower themselves to met the 2 tracks that the R-train uses that lead to/from from the Whitehall Street station, all of these tracks merge and form the two tracks that lead to/from the Court Street station in Brooklyn.

The inner set of tracks (2 tracks) have a diamond cross-over switch between them, so that either track can relay and terminate a train. These tracks "stub-end" at a distance so that both of the tracks can hold a full-length train. For example, an arriving J-train at Broad Street would discharge riders on the south-bound platform, enter one of the 2 inner tracks, and then return to the uptown platform ready for service.

Hope this helps.
Mike

Yes. Very detailed explaining of something I've always wanted to know! Thanks everyone .

This track map should answer your questions fully.