The next step is the communication. Not the main protocol, that will come later. This is for determining position. There will be metal plates between the rails and a contact on the bottom of the engines. When these touch, the engine's AVR will sense the pulse and send back its ID. That's all. For now, I prototyped this with an Arduino UNO and MEGA.
The communication flow through the yellow wire. There are 10K pull-down resistors to prevent catching noise in contactless state. I even draw a schematic.