On my web page, I describe the work that I've been doing to implement a method of train detection on my layout. My layout uses 3-rail tubular track so all of the work that I've done is with that kind of track.
I envision a scheme where there are RFID tag readers at strategic places around the layout (placed under the tracks). RFID tags are attached underneath every engine and car on the layout. Tags are loaded with information about the engine/car to which they are attached. A control computer could then use that tag information to control the engines.
I would use the Elechouse CC1101E radio and commands that I developed for the RTC program using OOK transmission codes.
Needs to be cheap. I chose the 13.56 MHz tags.
I plan to put two tags on each engine, one on the front truck and one on the rear truck. Cabooses will have one tag on the rear truck. All other cars will have a tag on one of the trucks. I plan on each tag having information about its distance from the end of the car. I hope to be able to couple/uncouple, pickup and drop off cars automatically via the control computer.
My scheme is based on Arduino computers and RFID tag readers from Elechouse. Each Arduino processes detection information for up to 6 tags. Any number of Arduinos then send this tag information to a Master Control Arduino. This computer uses the tag information know the position of every engine and car on the layout. This computer constructs commands which are sent over the radio to the TIU which forwards them on to track and to the engines. Here is a photo of one Arduino with one tag reader connected - with the RF antenna placed under the track:
My web page describes what I've done up until now and has a bunch of videos:
So what can we do with this? I envision a "smart" Master Control program which gets the tag information and controls the trains. Say, for example, you are running one freight train, doing switching to drop off and pick up cars. Let a computer run another freight train in the other direction. The computer would know where your train is and control the other train to take sidings to keep out of your way.
Or maybe, the computer controls a 1st Class train over the layout while you, controlling a peddler freight, have to figure out how to keep out of the way of the 1st Class train while still doing your work.
This video shows a short clip of a P&LE GP38-2 being controlled based on tag detections on my test layout.