Which type of signal is exclusively paired with a call-on signal?

The call-on signal is designed for situations where a train can proceed with caution past a signal that is otherwise indicating a stop. Specifically, it is associated exclusively with a home signal, which serves as a main signal controlling movement onto a track. When a call-on signal is illuminated alongside a home signal, it instructs the train operator that they can proceed at a restricted speed past the home signal to reach a block that is clear or to enter a new section of track.

Home signals provide the primary control for train movements and are typically the first signal encountered on a route. The pairing of a call-on signal with a home signal ensures that train operators understand they must approach the next block with caution, following the specific rules associated with the call-on indication. This relationship is crucial to maintaining safe train operations in areas where signals dictate the flow of train traffic.

Other types of signals mentioned do not have this exclusive relationship with call-on signals. For instance, clear signals and caution signals indicate different states of track conditions without the specific implication of a call-on scenario, while a stop signal denotes an absolute halt rather than the option to proceed cautiously. Thus, the home signal is fundamentally linked with the call-on signal and serves a critical regulatory role in train operations.