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A failsafe system of train operation primarily used for single line routes. The ball token system relies on the crew's physical acquisition and carriage of a small metal ball to mark a train's permission to enter a section of track. The ball is dispensed by a Token Instrument at either end of the block. The two instruments are interconnected so that at any given time, one and only one ball can be handed out from either of them, ensuring that only one train from either direction can enter the section of track controlled by them. This system is now being replaced by modern signaling, thus marking the end of an era.
