Model Train Technology

Merging Tracks Signaling A

Version A uses three-aspect signals with the same wiring as version B, including the detector on the shared track past the merge. When a track releases the shared track, its signal steps down through yellow to red.

Merging tracks relay interlock with a detector past the merge Detectors 1 and 2 feed their controllers through normally closed relays K1 and K2, which are cross-wired so only one track can get a green. Detector 3, on the shared track past the merge, feeds both detector lines through a diode at each connection. Track 2 Track 1 Shared track Detector 2 Detector 1 Detector 3 Diode Diode B A Relay K2 (normally closed) Relay K1 (normally closed) coil coil Controller 2 Controller 1 Signal 2 Signal 1

Active detector signal Inactive wire Train

How the yellow aspect works

Each signal controller shows green while its detector line is active. When the line drops, the controller steps the signal down through yellow for a moment before red. The wiring is identical to version B, so the interlock behaves the same way.

Detector 3 feeds both detector lines through diodes, ahead of the relays, so it’s locked out by the same relays as detectors 1 and 2. A train must reach detector 3 before it leaves detector 1 or 2.