A railway signal is a visual display device that conveys instructions or provides warning of instructions regarding the driver's authority to proceed. The driver interprets the signal's indication and acts accordingly. Typically, a signal might inform the driver of the speed at which the train may safely proceed or it may instruct the driver to stop.
Colour-light signals (Great Britain)
The additional lights on Japanese signal 10 show that the points are set for the left route at the next junction.
Some signals convey large amounts of information. This older German signal indicates preliminary caution with max. 60 km/h in the upper main signal aspect (green above yellow, number plate "6") and caution in the lower distant aspect. The lower yellow number indicator announces a speed limit of 30 km/h by displaying "3". At that specific station the selected route ends on a stub track, thus distant caution with additional speed limits.
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.
Train order operation is a system for safely moving trains using train orders, as opposed to fixed signals or cab signalling. In train order operation, a "train order" is an order issued by or through a proper railway official to govern the movement of trains".
Picking up train orders on the ATSF in Isleta, New Mexico in 1943
A train order issued in the United States in the 1940s
