A safety mechanism mounted on the leading truck of a locomotive or transit car that interacts with a trackside trip arm. If a train attempts to pass a signal displaying a stop aspect, the raised trackside arm strikes the tripcock, immediately venting the brake pipe to atmosphere and throwing the train into an emergency stop.
Heard on the job
The train hit the tripcock at the interlocking because the motorman missed the red aspect in the tunnel.
Also heard as
- trip valve
Related terms
Train stop
A mechanical or electronic trackside device that forces a train's brakes to apply if it passes a red signal.
Automatic train control
A safety overlay system that enforces speed limits and signal indications without engineer input.
Signal passed at danger
A severe safety violation where a train moves past a red or stop signal.