All the boxes I sign - and, as far as I'm aware, it's standard on all non-LU lines! - have exactly the opposite. There's usually a pair of lamps (or more) per track circuit (rather than the track itself lighting up!) - so two would have to blow before a train would 'disappear'. I assume (though I can't be totally sure) that the interlocking's fail safe though - even if the lamps did fail to light, the locking would still prevent us pulling off for one.Signalman said:Its a fail-safe design. If a bulb blows we have to assume a train is there. What do you have?