Diagram A The situation if there is no crossing at this station.

Diagram B The original automatic signalling installation was Single Line Automatic (SLA) with automatic operation of points and signals. The branch is now operated by CTC but the double yellow feature of SLA has been retained.

Diagram C If the line is in "Auto" mode, then after the down train enters the station and clears the points and section behind, a 30 sec time delay runs. At the end of that time the block is released. The up "Distant" indicates yellow if the down train already at the station has been there less than 30 secs. Once more than 30 sec have elapsed, the Up intermediate would change to green. If the Train Controller has taken manual control then it is entirely possible that all three Up direction signals would be a green already.

Diagram D This move is allowed, but the preceding service would have had to be inside the home and clear of the points for 30 secs to release the block to the following movement, so it would be a rare event.

Diagram E This is standard CTC. Under automatic operation running is left hand but Train Control can take control if required.

Diagram F The installation of Advance Caution (flashing yellow on top unit) has been proposed for the Johnsonville Line. This will mean that the "Distant" will indicate yellow only when the Home signal is at Stop or Low-Speed

Distant Or Intermediate In the original SLA installation the "distants" were designated R3 etc (repeater for 3 signal). The system was designed so that the "distants" could be replaced by intermediate signals. In 1969 the "distants" were renumbered as intermediates but I do not know if their function changed or if they now allow following moves.