"AF Track Circuits" . . . "disappeared" . "Track circuit#Circuit_failures" . . "Track Circuit" . "track circuit block" . "Track circuit" . "track circuit operating clips" . "Track Circuit Block" . "detect the presence of the train" . . "track circuit-based system" . "Track Circuits" . "Track circuit" . "jointless track circuits" . . "track circuits" . "DC code systems" . "track-circuited" . "track circuit" . . "track-circuiting" .