Route relay interlocking

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Route relay interlocking (RRI) is a system that was often used in large and busy stations that have to handle high volumes of train movements. In this, an entire route through the station can be selected and all the associated points and signals along the route can be set at once by a switch for receiving, holding, blocking, or dispatching trains. Since the 1980s, new interlockings have tended to be of the electronic variety.