reversals are necessary.
The white train (from A to D) is divided into three sections, engine
and 7 wagons, 8 wagons, and 1 wagon.
The black train (D to A) never
uncouples anything throughout. Fig. 1 is original position with 8 and 1
The black train proceeds to position in Fig. 2 (no
The engine and 7 proceed towards D, and black train backs,
leaves 8 on loop, and takes up position in Fig. 3 (first
Black train goes to position in Fig. 4 to fetch single wagon (second
Black train pushes 8 off loop and leaves single wagon there,
proceeding on its journey, as in Fig. 5 (third and fourth reversals).
White train now backs on to loop to pick up single car and goes right
away to D (fifth and sixth reversals).