In this application the MR204 is used as a Automatic Forward / Reverse (Shuttle) Control. Sensor 1 and Sensor 2 could be placed anywhere on a loop, or even back to back. The train will run from Sensor 2 to Sensor 1, when it passes sensor 1 the circuit will change the polarity of the tracks putting the train in reverse. The train will now travel in reverse until it passes over sensor 2, at which time the MR204 will again change the polarity of the track putting the Train into forward again.
This will continue until power is removed from the system.