Here is the position at the start. Eastbound train has one coal car. Westbound train has two cars, a gondola and a boxcar.

Move 1. Westbound loco heads into the spur, leaving cars on
the main.

Move 2. Eastbound loco moves past the switch and pushes the cars  farther along the main.

Move 3. Westbound loco returns to the main and couples to the coal car.

Move 4. Westbound loco pulls coal car past switch.  Move 5. Eastbound loco goes to spur.

Move 6.  Westbound loco reverses back past switch and couples to all three cars.

Move 7.  Westbound loco pulls cars past switch and stops.

Move 10. Eastbound loco pulls all three cars forward and clear of the switch.

Moves 11 and 12. Eastbound loco backs coal car into spur, stops  and returns to main.  Move 13. Westbound loco backs onto cars.

Move 14. Westbound train pulls away and proceeds on its journey.

Move 15. Eastbound loco backs into spur.

Move 16. Eastbound train, once again intact, pulls away and continues on its journey.