An electronic display mounted in the engineer's field of vision that continuously relays the aspect of the block signals ahead. It receives coded electrical pulses from the rails. If the signal drops to a more restrictive aspect, an alarm sounds in the cab, requiring the engineer to acknowledge it and reduce speed.
We caught a restrictive cab signal just past the crossover, so I had to dump the air.
Operating with a failed cab signal system usually imposes severe speed restrictions on the train.
Related terms
Block signal
A fixed trackside light or semaphore that tells an engineer whether the track segment ahead is clear.
Aspect
The visual appearance of a trackside signal as seen by an approaching locomotive crew.
Alerter
A cab safety device that applies the brakes if the engineer stops moving the controls or pressing its reset.