A fixed signal at the entrance of a block section that governs trains entering and using that segment of track. It displays an aspect indicating whether the track ahead is occupied, clear, or requires restricted speed. These signals are tied into track circuits that automatically detect the presence of axles, ensuring trains maintain safe separation.
Heard on the job
The block signal dropped to red right as we passed the approach, so we had to dump the air.
Insider tip
A block signal governs the space between trains, whereas an interlocking signal governs the routing of trains over switches and crossings.