Editing Cab signalling (section)

{{Short description|Railway safety system}}
{{use dmy dates|date=March 2022}}
[[File:CTA Cab-signal-display.jpg|thumb|upright|Cab signal display unit on a [[Chicago Transit Authority]] [[Chicago 'L'|'L' train]]. The vertical light bar in the middle of the signal indicates the maximum permitted speed for the section of track where the lead car is currently located.]]

'''Cab signalling''' is a [[railroad|railway]] safety system that communicates track status and condition information to the [[cab (locomotive)|cab, crew compartment or driver's compartment]] of a [[locomotive]], [[railcar]] or [[multiple unit]]. The information is continually updated giving an easy to read display to  the [[train driver]] or [[Railroad engineer|engine driver]].

The simplest systems display the trackside signal, while more sophisticated systems also display allowable speed, location of nearby trains, and dynamic information about the track ahead. Cab signals can also be part of a more comprehensive [[train protection system]] that can automatically apply the brakes stopping the train if the operator does not respond appropriately to a dangerous condition.<ref>{{cite book| title = Elements of Railway signaling| work = General Railway Signal Co. | url = https://books.google.com/books?id=LjIvnQEACAAJ | date = June 1979| publisher = General Railway Signal Company }}</ref>

The main purpose of a signal system is to enforce a safe separation between trains and to stop or slow trains in advance of a restrictive situation. The cab signal system is an improvement over the [[Railway signal|wayside signal]] system, where visual signals beside or above the right-of-way govern the movement of trains, as it provides the train operator with a continuous reminder of the last wayside signal or a continuous indication of the state of the track ahead.