I watched the Via Rail Veterans train whizz by a junction tonight.
The signal was green over red before the train came. As the train enter the block, the top head changed from green to red, winked at me (went dark for less than a second) and then returned red.
A short while later, as the train left the block, I expected some new combination, perhaps a yellow / red, (Rule 409), to indicate that the next block is occupied. Instead, both heads went dark, and stayed that way.
The signal you saw was probably an intermediate signal simply advising of the condition of the block ahead. These signals are usually approach lit, which means when a train gets close enough the signal will light up. When running on trains at night I used to see the signals light up ahead of me. Absolute signals, I belive, are always lit and never go dark. When no trains are lined up they simply stay lit red. Not positive on that.
Here on the Pocahontas Division of the NS we have some signals that go dark after a train goes by it.I was told it is an energy saving mode.Also in some places thats out in the boonies,it keeps people from taking aim at the lights with guns.The signal that fickers after a train goes by it ,is sorta normal because after the train “knocks down” the signal it has to reset to stop or restricted.And it may have an issue with the signal bond wire. What I have noticed on some signals is the distance it takes a train to “drop” a signal to red after it “knocks” it down .But run a stop signal and the dispatcher can sure tell real quick.I’m sure it doesn’t flicker on their computer.
When the train changed the top head from green to red, the holder of the three colored roundels was de-energized. Red is the default position. What happened was that the mechanism swung past the red position a bit, then settled back to the red position. Nothing to panic over.