Railway signal
A railway signal or just signal is a mechanical or electrical machine that gives train drivers or engineers information about the line ahead. These traffic signals say whether the train must stop or may continue and what speed the train may go.
In Britain, modern signalling uses a system similar to road traffic lights. The signals are coloured lights mounted on a pole. A red signal means 'do not go further'. A yellow signal gives a warning to the driver that the next signal is showing a red. Some signals can show two yellow lights, known as a "double yellow" and are warnings to the driver that the next signal is showing a yellow. A green signal means 'you can continue'.
On older lines semaphore signals are still used. These are poles with a coloured bar at the top, which can be moved so that it is either horizontal, or at an angle. When a red bar is horizontal this means that the train must stop, and when it is pointing diagonally up or down it means that it's safe for the driver to continue. There are also signals with yellow bars which give warnings in the same way as yellow lights on newer signals.
Railway Signal Media
The additional lights on Japanese signal 10 show that the points are set for the left route at the next junction.
A British lower-quadrant semaphore stop signal with subsidiary arm below
A Finnish distant signal at the western approach to Muhos station is displaying Expect Stop. In the background, express train 81 is pulling away from the station.
Mechanical semaphore signals at Kościerzyna in Poland
Network Rail (UK) two-aspect colour light railway signal set at 'danger'
German railway signals showing aspect Hp0 (Stop)
Railway signal in Ploiești West railway station, Romania. This type of signal is based on the German Ks signals.
Mechanism of a searchlight signal made by Union Switch & Signal, with the lamp and reflector removed to expose the coloured roundels
PRR position light signal showing "Approach Medium"
