A few more things about this method -
To ensure automatic signals stay red until the path is set, make the default direction of each junction (the direction of the red/green arrows in surveyor) within a path lead onto a dead end. As already mentioned, the SnC semaphores don't like having an aspect forced on them, also I seem to remember that Bloodnok's MAS colourlights also don't keep a "Set Signal State".
I think (more testing needed to definitely confirm) that junction directions are not changed unless all the permits for a path have been obtained. This avoids the "fiddler's elbow" effect mentioned in the 2nd link in pwjohnson' s post above where a path part-completes, allowing a signal to clear, then un-sets as the full path is not available.
By carefully positioning triggers, when a path sets can be controlled. A class 1 express would be set to use a trigger a long way before the junction, to reserve the path with priority over any other train; a slow freight of lower priority would use a trigger much closer while "approach release" can be used by having the trigger only just before the start of the path - remembering that the signal is held to red by the default dead-end path.
By using Check Consist, On Time, etc, rules, with set Driver Schedule as a child rule, it is possible to send fresh "select path" command to your player train to get the player train to run to it's schedule. As a simple test I have manually driven my train into a loop, watched a following AI train re-set the path, clear the signals and pass, then at departure time waited for signals to clear and then driven my train back onto the main line.
Hope this helps.
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