gunrunnerjohn posted:Well, bidirectional control kinda' implies multiple tracks. Having signals that react to trains going different directions on the same tracks would require some capability of determining the direction of travel. This can be done with multiple IR sensors for a block, but not really using insulated tracks.
Terry at Custom Signals had a board called a "Tumble Down Controller" that was made for this application and used insulated rails. If you have single track between town A and town B with multiple signal blocks along that track, the board detects when a train enters the single track from town A. All of the signals in the opposite direction (from town B to town A) are automatically set to the STOP indication.
Signals in the direction from town A to B act according to automatic block signalling (when the train has moved completely into the second block, the signal at the beginning of the second block displays STOP while the signal at the beginning of the first block changes to APPROACH.
