To make it a bit simpler, a few of the rail rules have been revised, this is the result:
A player may connect locally to one station per build/zone they're in. The player decides which of the 4 stations they want to connect to. All railways must be underground. Once you've connection to a station, post which connection you've used in this post.
Player may connect to other players in the same 'square', using underground tunnels that won't be in the way of other peoples (future) builds.