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A post-mounted board marked W or SW.
Also known as: Sound whistle board, Horn board, W board, Board marked W
A whistle board tells the driver to sound the horn — usually approaching a level crossing where sighting is poor. Some are marked SW for 'sound whistle' and some carry time restrictions, because a horn at 3 a.m. through a village is a different problem from one at midday.
Instructs a train driver to sound the horn at that point, typically on the approach to a level crossing.
Contexts: Public information
Carries time restrictions on some networks, suspending the requirement overnight where noise nuisance outweighs the warning value.
Contexts: Public information
A small rectangular or diamond-shaped board on a lineside post bearing a large letter W, sometimes with the letters SW or a time restriction beneath.