traffic movement may be either fixed-block or moving-block.

;Fixed block signaling

Most blocks are 'fixed' blocks, i.e., they delineate a section of track between two defined points. On timetable, train order, and token-based systems, blocks usually start and end at selected stations. On signaling-based systems, blocks usually start and end at signals. Alternatively, cab signalling may be in use.

The lengths of blocks are designed to allow

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