Abstract: In a railroad interlocking, a cab signal transmitter is coupled to the rails at each exit location and at such other locations as are necessary to supply continuous cab signal energy to trains traversing any possible route through the interlocking. Where train shunts prevent the reception of cab signal energy, wire loops laid adjacent the rails carry the cab signal energy for train pickup. Each rail coupled transmitter is finally activated to supply energy when a train occupies an associated track section. However, the control circuit network for each transmitter also checks, as pertinent for the established route, that a route has been established and the approaching train authorized to traverse that route, that any succeeding track sections along the route are unoccupied, that the transmitter for a preceding section has been activated, and that transmitters for opposing or conflicting routes are not active.

Abstract: A single relay serves to register route request selections for both traffic directions over each track route through a railroad interlocking layout. This single route request relay is jointly controlled by the route selection push buttons for both directions, the actuated push button being also repeated by a traffic direction relay. The route request relay pick up checks that no conflicting route request is active, and that the same or opposing route is not already established and locked. The route request and direction repeater relays are held by stick circuits to store the request until the route is locked. A single relay serves to provide the clear and lock function for all possible traffic routes originating at each entry point into the interlocking.