Finally had some time to visit your site and ... amazing project.
My system working at DC mode. So, not need detect the position of a particular train.
Post #25 mentions hall sensors.
You can stop a particular train in front of a traffic light by removing the voltage from the section of rails in front of it, as on classic DC.
It seems to me a very abrupt way to exercise control. All the passengers' coffees will be spilled.And it's not how the real railway works ...R
All right thank you very much, anyway. It was an interesting discussion.