A traditional mechanical trackside signal that displays its aspect through the physical angle of a pivoting arm or blade. A horizontal blade typically indicates stop, while a diagonal or vertical blade indicates proceed. Although largely replaced by high-visibility color light signals, they remain an iconic piece of historic railroad infrastructure and are still maintained on a few remote branch lines.
We still have one old semaphore signal guarding the junction out by the lumber mill.
Related terms
Signal aspect
The visual appearance of a railway signal that conveys a specific rule to the crew.
Color light signal
A trackside signal that uses illuminated colored lenses to convey track authority.
Block signal
A fixed trackside light or semaphore that tells an engineer whether the track segment ahead is clear.