Cab Controls
All D-class trams have a traction braking controller with an integral deadman's trigger that the driver must release and reapply every minute. If this is not done, an alarm sounds. If the alarm sounds for more than a few seconds then the disc brakes are applied firmly, stopping the tram.
Originally the driver could hold it down continuously while the tram was moving, if the driver took their hand off, an alarm would sound, followed soon by track brake application. If after four minutes it had been held-down continuously and the tram stopped, the driver would get an audible warning and the tram would not move until the driver had released it. There was also an alternative deadman's button on the side of the armrest. Drivers discovered that if the armrest were dropped low enough, this button would stay pressed without the driver applying any pressure, they still had to be released every four minutes when coming to a stop. But as soon as the management discovered this, their reaction was "vigilance control," actually a dead-man's vigilance device, and hence the notice in the cab "Vigilance control now fitted, release and reapply every minute, if an alarm sounds, release and reapply immediately."
Read more about this topic: D-class Melbourne Tram
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