The RFID system I developed about 10 years ago consisted of a PIC based board. It wasn't computer controlled but a stand alone system tied into the Atlas signal system. When a train approached a red signal the RFID reader under the track would read the engines TAG and then generate the proper engine commands to stop the train. It would also blow the horn/whistle ( 1 toot). When the signal turned green engine commands would blow 2 toots and start the train up.