unsignaled

Unsigned is an adjective meaning not marked or indicated by signals; lacking signaling devices, warnings, or explicit notification. In transportation, the term is widely used to describe level crossings (railroad tracks that cross roads) where no active warning devices exist. An unsignaled crossing may have only signage (crossbuck, stop or yield) and rely on drivers to observe trains; there are no gates, lights, or bells. Such crossings are more common in rural or low-traffic areas and are often subject to safety upgrades, speed reductions, improved sightlines, or, in some cases, closure or grade separation. Safety concerns include higher chance of collision due to the absence of automatic alerts. Many jurisdictions collect data on unsignaled crossings and implement programs to install signals or build alternatives.

In railway operations, "unsignaled" can describe a track section or route not protected by fixed signal devices. Movements through unsignaled blocks or sections are governed by timetable rules, train orders, or token systems and require careful crew procedures and communication to avoid conflicts. Advances in signaling have reduced reliance on unsignaled routes, but some networks retain them in remote or low-density lines.

The term can also appear in general language to indicate something that lacks signaling in a broader sense, such as an unsignaled event in a process or system, though this usage is context-specific and less standardized.

Etymology: formed from un- + signaled, documented in 19th-century discussions of railway signaling and general signaling terminology.