Dunno much about trains but how far away from the traffic light would the button be? Certainly not more than 256 x wagon.length. I.e. in the unlikely case of a

Dunno much about trains but how far away from the traffic light would the button be? Certainly not more than 256 x wagon.length. I.e. in the unlikely case of a train with 256 wagons the light will signal green (unfortunate) but while it does so there will be a train passing by the crossroad. So in that case only (257 wagons won't do it - they'll merely cause a green blip) you'd need to have a really pedantic driver at wheel to try to pass because light went green.