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Wig-wag signals are traffic signals consisting of a set of three lamps mounted on a rectangular board, with an upper pair of horizontally aligned red lamps which flash alternately ('wig-wag') when in operation. The lower lamp is amber.
They are used for a variety of purposes, including the protection of level crossings, lifting or swing bridges, and the exits from fire stations. It is an offence to pass a stop line guarded by the flashing red signals.
The boards on which the lamps are mounted are invariably black, and normally have a red and white chequer surround, although a narrow plain white edge is occasionally used.
The most common use of wig-wag signals is to protect level crossings. However, as mentioned above, they are also used widely to warn of opening bridges and of vehicles emerging from fire stations as well as in a range of other situations where the road ahead may be blocked at random times of day. More regular blockages, such as those occasioned by cattle being taken for milking have simpler warning lights.
In addition to the two, alternately flashing, red lamps at the top of the board, there is also normally a single amber lamp lower down. This is used in a similar fashion to the amber light on standard signal heads, warning that the red signal is about to be lit and that approaching vehicles should stop if they can do so.
Isle of Man
In the Isle of Man wig-wag signals are mounted as if they are a normal 3 aspect traffic signal, with the exception that the top and bottom lamps are red, while the middle is amber. The signals are mounted onto a red and white backing board.