A dead-man's vigilance device is a railroad safety device that operates in the case of incapacitation of the engineer. It is a hybrid between a dead-man's switch and a vigilance control.
The main safety failing with the basic dead-man's control system is the possibility of the operating device being permanently held in position, either deliberately or accidentally. The dead-man's vigilance device was developed to detect this condition by requiring that the dead-man's device be released momentarily and re-applied at timed intervals.
Modern locomotive practice is to incorporate the dead-man's and vigilance functions under the control of the Alerter (US) or the event recorder. This enables more sophisticated monitoring of the driver's alertness. The vigilance control cycle time can then be speed dependent, varying inversely to train speed in order to reduce the distance the train may travel before a non-response is detected and acted upon.
In addition to the dead-man’s pedal/button, the reset signal can also be any one of a number of train handling control actions already monitored by the event recorder. These include a change of throttle position, brake or horn operation, all indications that the driver is actively controlling the train.
If the timer period is allowed to expire a visual and audible warning is given by the Alerter or similar warning device. If the operator fails to acknowledge the warning, a Penalty Brake application results.
Vigilance control is not foolproof and should not be taken to indicate that the driver is vigilant in the true sense of that word. This is because it does not measure driver alertness, merely requiring the robotic response of button pressing. Such responses can occur without conscious input by the driver – the driver could be effectively asleep, drunk, or otherwise unaware of his environment and still automatically respond to the device.
Read more about Dead-man's Vigilance Device: Accidents Due To Insufficient Vigilance Control
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