Automatic warning systems (AWS) identify approaching trains and warn workers in the vicinity of the tracks using acoustic or visual signals. Detectors that are secured to the inside of the rails at the start of the approach route are used for this purpose. The flange of the train wheel trips a switch on the detector, thus activating an electrical impulse, and, as a result, the warning signal.
Automatic track worker warning systems of this kind are available either as combined signal systems or as individual warning systems. In the case of combined signal systems, either electro-acoustic sirens or flashing lights are activated as a warning signal. Individual warning systems issue acoustic or visual warning signals, or activate vibration units, directly for each individual worker. Signal-independent safety systems provide a third variation. In this case, the section of track can only be approached once confirmation has been received that the maintenance site has been cleared.
As a considerable amount of effort is required to install automatic warning systems, they are only deployed for larger engineering works. Signalling personnel are nevertheless required, despite automation: the functionality of the system must be monitored, warning signals repeated if the tracks are not cleared immediately, and approaching trains stopped in emergencies.
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