OK heres my take on Relay shuttle operation.......
Line consists of single track with station at each end(A+B)
Starting off in the middle of the line heading towards station A. The relay "Coil" is denenrgised(down).As the magnet fitted shuttle passes over Reedswitch A, Placed at a suitable point approaching station A, it momentarily makes the normally open (NO) contact closed. This allows the relay Coil to energise, and in so doing alters the change over switch(COS) "Coil1"to close the NO switch, completing the circuit through Reedswitch B and sticking the relay coil in an energised(up) state. This change of state is then used to change the direction of the shuttle via COS "Coil2" and "Coil3" A further COS "Coil4" is used to change the signals to clear/on as appropriate. At the other end, the Normally closed (NC) switch on Reedswitch B, placed at a suitable point approaching Station B, breaks the previously made circuit and swaps traction polarity sending the shuttle back to A.
I would imagine that a suitable capacitor across traction supply.....NON POLARISED!! Would smooth the changeover, to stop the gears of the shuttle being damaged.
Of course the problem here is there is no pause at either end. For that, you would need a 555 timer........
1 x 4COS relay
2 x COS Encapsulated Reed switch.
LEDs for signals
Suitable resistor for signal LEDs
I think that would work OK, total cost less than a tenner.