fog signal

plural fog signals

1. UKrail transportA small explosive charge (detonator) which can be placed on a railway line in fog, to be detonated by a train passing over it as a warning signal to the driver.

   The last train—a three-coach A.E.C. unit—from Belfast to Crumlin and back, was bade farewell with fog signals as it carried a capacity crowd of last-trip travellers.

   1960 November, L. Hyland, “The Irish Scene”, in Trains Illustrated, page 691

   1 more example

   The layman does not realise the dreadful nightmare of running in fog, especially at night, when the safety of everyone depends on the driver hearing the fog signal detonate.

   1943 November and December, T. Lovatt Williams, “Some Reminiscences of the Footplate—III”, in Railway Magazine, page 344