Hauptsignal

Hauptsignal, in railway signaling, is the main signal used to control train movements on a given route or block section. It conveys permission to proceed or to stop, depending on the current routing and safety conditions. Hauptsignale are typically part of an interlocking system that ensures safe movements and are usually accompanied by Vorsignale, distant signals that inform the driver about the status of the upcoming main signal. The presence of a restrictive Vorsignal requires the driver to prepare to stop, while a clear Vorsignal indicates that the main signal is likely to show proceed or that the route is set.

Historically, Hauptsignale were mechanical semaphore arms; in modern networks they are electric signal lights, often with standardized color aspects. The exact appearance and meaning of the aspects depend on the signaling regime used in a country or network, but the general purpose remains: authorize passage through a section of track or require a stop.

In operation, a train observing a Hauptsignal applies the instructions associated with its current aspect and the route's speed restrictions, and will typically encounter subsequent signals in sequence along the line. The system relies on interlocking to prevent conflicting movements and to ensure that a main signal can only show proceed when the route ahead is confirmed clear.

See also: Vorsignal, Interlocking, Semaphore signal, Signal box.