Cab signalling is a railway safety system that communicates track status information to the cab, crew compartment or driver's compartment of a locomotive, railcar or multiple unit, where the train driver or engine driver can see the information.
The simplest systems display the trackside signal aspect (typically, green, yellow or red, indicating whether it is safe to proceed or not), while more sophisticated systems also display allowable speed, location of nearby trains, and dynamic information about the track ahead.
In modern systems, a train protection system is usually overlaid on top of the cab signalling system to warn the driver of dangerous conditions and to automatically apply the brakes and bring the train to a stop if the driver ignores the dangerous condition. These systems range from simple coded track circuits to transponders that communicate with the cab, to communication-based train control systems.
Read more about Cab Signalling: Overview, Hierarchy of Cab Signal Systems, Information Transmission, Typology of Cab Signalling Systems, Cab Signalling Systems in The US, Positive Train Control, Audio Frequency Track Circuits
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