The earliest systems were train stops, as still used by the New York City Subway, the Toronto Subway, the London Underground, the Moscow Subway (only on the older lines) and the Berlin S-Bahn.
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Transmission balise-locomotive (Dutch: Transmissie Baken Locomotief) (TBL) (English "Transmission Beacon Locomotive") is a train protection system used in Belgium and on Hong Kong's East Rail Line.