Study guide 11.1

[steak]

Have a look for Treadles (often used for Level Crossing strike-in)
Look up Rail circuits - I can't say I know much but I think they're an inverse of Track circuits.

Signal aspect sequences need to prove the absence of a train, similarly for moving points we prove there is no train on the points that might be derailed.

Level Crossing strike-in can probably be argued both ways - the sequence is initiated to lower barriers by a train approaching, but equally barriers are only maintained open by proof of no approaching train.

I'm probably thinking about it from a more Mod3 point-of-view though.

thanks