What I have in mind is a two part setup. Both the trigger and the crossing will need to be scripted and, as I have little or no interest in building 500 level crossings, it would be useful to be able to attach the crossing script to existing objects.
The trigger will need to know which crossing it is talking to, how far away it is and how long its animation takes to run. It will need to detect a train and the speed at which the train is travelling. It will then need to work out how long it will take for the train to get to the crossing and when the gates should close. It will wait until the appropriate moment and then send a message instructing the crossing to run its animation.
I'm reasonably sure that all of this is possible in TRS2006, and it should also be possible to extend the concept to send messages to signals and junctions.
The crossing script will just need to turn off the built in auto response mechanism, listen for 'Train Approaching' messages from the triggers and, once the crossing is clear of trains, close itself. This can probably be set up as a standard script which can just be dropped into existing unscripted crossings.
Since crossings can control road traffic only as well as road and rail together the situation that Stagecoach is describing could also be covered directly (ie without the dummy junctions). I'm not minded to further support the AJS Crossing Controller - it was always a bodge and is unneccessary under TRS2006.
To quote from a recent trainz newsletter:
Trainz Classics will feature:
...
-Train controlled sounds, lights and boom gates at build-in road crossings
-New Freeways feature supporting and including one way and multi-lane roads
-Remodelled roadway traffic featuring working head lights
...
So Auran are planning to implement their own 'Street Kit' - where do I send the bill?
Assuming that they make a better fist of this than they did with their 'Junction Kit' there will probably be additional facilities in the next release so don't expect this immediately. I will start looking at it though and it would be useful to hear anybody else's thoughts on the subject.