A different tack might be to install a relay or equivalent in the engine to cut power to just the motor leaving full track power to the electronics. Whatever detects the higher priority train would activate some signal on the lower priority track section that activates the motor cutoff relay. Certainly not as impressive as the RFID/computer control techniques but ought to be relatively inexpensive - maybe $10?
I have not done this myself but would be curious if someone else has tried this. I have some additional thoughts on this if this approach adds to the discussion.
