blocksignaler

A blocksignaler is a component of railway block signaling systems that communicates the occupancy status of a defined section of track (a block) to train drivers and to signaling control equipment. In traditional fixed-block systems, the blocksignaler is tied to track detectors such as track circuits or axle counters and drives the adjacent signal aspects to indicate whether the block is occupied or clear. In modern installations, the blocksignaler is an electronic or electromechanical subsystem that processes inputs from detectors and outputs control signals to signals and interlocking logic.

Responsibilities include monitoring track occupancy, enforcing safe distances, and cooperating with the interlocking to prevent conflicting movements. The blocksignaler is typically located at block boundaries or signaling control points and is integrated into a broader signaling architecture, such as centralized traffic control or moving-block systems, for route authorization.

Blocksignalers are designed with fail-safe principles: a loss of power or detector fault generally defaults signals to the most restrictive aspect to protect trains. They are interlocked with other signaling devices so that routes cannot be set unless the block is verified clear, and so that a train entering one block is reflected in subsequent signals.

Over time, signaling standards have evolved from mechanical semaphore to electric-light signals, and later to digital interlocking schemes. The term blocksignaler is used chiefly in discussions of block signaling systems and may refer to any unit that performs the signaling and interlocking logic for a particular track block.

See also: block signaling, interlocking, track circuit, axle counter.