This trigger simulates the action of a UK call-on or similar permissive signal aspect. Place it 5 - 10m in rear of a signal that can display either the EX_STOP_THEN_CONTINUE aspect (1) or the EX_STOP aspect (9). When a train approaches from in rear of the trigger, the signal will be set to display the appropriate aspect PROVIDED that there is enough room in advance of the signal to accomodate the train without fouling the signal or any intervening junctions. When the train has passed the signal, it is restored to automatic operation.
Suitable signals include 'Signal BR 1' to 'Signal BR 3' and their right-hand equivalents (built-in in TS2009 & TS2010)
Trainz AIs are reluctant to drive right up to other trains (unless coupling), so it's best to allow plenty of space. At the moment, the trigger looks for an additional 30m over and above the length of the train that triggered it.