They'll be TOWS - Train Operated Warning System. They are used to provide an automatic warning of an approaching train, and can be switched on when gangs are working at the location.
They have a wailing siren on the stretch of ECML through Grantham station, which, when switched-on, not only sounds when trains are approaching, but also sounds intermittently when there are no trains in order to test it.
Very necessary on this fast stretch of line with a curve to the north end of the station, but very noisy too if you're on the platform at the time.
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Also another query I have is that am I right in thinking that only one train can be in Standedge tunnel going in one direction at a time, in other words if a train is going towards Manchester another train can't enter the tunnel until the first train has exited the tunnel at the other end.
I seem to remember from a cab-ride video I saw a while back, that there is a colour-light signal within the tunnel towards the eastern end, but by the time the train has cleared it, it would be out of the tunnel before the next one could enter from the western end. Is that signal still there, or am I imagining it?
There were even watertroughs within the tunnel at one stage, but that is going back a bit!