1973 Tube Stock (73TS) uploaded!

Hi John,
Yes - it's certainly possible to follow a train ahead of you. The route has been built with all the correct signal types at the right locations, per the track and signal diagrams for the real lines, so any prototypical move should be possible.
The picture you noted does show a situation that occurs in real life. The Picc 73TS (Player train) has left the WB fast lines from ACT Pfm 2 and is heading up the bank - ultimately towards Rayners Lane. The D78 (AI) left the slow line from Pfm 1 heading for EBDY. These two lines join at the bridge ahead, from where the Picc and DL share the track through ECM and then split again at the HLJ bridge. In the picture shown, the Picc train 'got the road' ahead of the D78 (i.e. our route was set), so the DL train had to wait, and will be following us once we clear the section. Had the D78 got the road first, we'd be following him through ECM - our progress controlled by the signals as he clears sections ahead of us.
Which train does what is all down to the activity maker, as defined by the various train timetables and paths. I deliberately set up that situation to test that the route-setting logic and signals were doing what they should ;D
To give you a sense of what can happen in this busy section of the route, here's a track/signal map of the MSTS route:



Each 'blob' next to the tracks is a signal! There are a lot of both converging and diverging paths in this area on both the EB and WB tracks, as well as access to/from ECM Depot and the East and West sidings, and Acton Works. Any documented 'move' for both Picc and DL trains should be possible - including shunt moves.
So it is up to the activity designer to create the correct paths for any service, and to set their timetables. The route setting logic and signals will control train progress. This will lead to realistic 'conflicts' or waiting for a path to clear due to other traffic - many of these doubtless familiar to the train operators on this board
Sorry if this was long-winded, but I though I'd give you a broader sense of what can be done.

Best, Jimi