Fixed signals are signaling devices that are permanently installed at designated locations along a railway line. Their purpose is to provide train crews with movement authority and information about track conditions ahead.
The term "fixed" refers to the fact that these signals remain at a permanent location and do not move with the train. Train crews must observe and interpret the signal indications as they pass each signal location.
Fixed signals are commonly mounted on signal masts, cantilever structures, signal bridges, or other permanent installations located beside or above the track.
These signals communicate information through visual indications. Modern signals typically use colored lights such as red, yellow, green, lunar white, or blue. Older systems may use semaphore arms or position light arrangements to display signal indications.
Every signal indication displayed by a fixed signal is known as a signal aspect. Each aspect has a specific meaning that is defined by the railroad's operating rules.
Signal aspects may instruct a train to stop, proceed, reduce speed, approach the next signal prepared to stop, or follow a specific route through an interlocking.
Fixed signals also provide information about conditions ahead, including occupied blocks, track conditions, switch alignments, and movement authorities granted by the signaling system.
At interlockings and control points, fixed signals may display route information indicating which track or path a train has been authorized to follow.
Safe train operation depends on train crews correctly interpreting signal aspects and complying with all operating rules associated with those indications.
Failure to obey a fixed signal can result in serious operational and safety consequences, including train collisions, derailments, or violations of operating rules.
Fixed signals remain one of the most important safety devices used in railroad operations and continue to provide the foundation for many modern signaling systems.