After the next couple of bends the gradients ease, and in real life the banker loco would stop pushing, and roll back down the hill to Stella Gill Flatts where it would wait to assist the next train.

This is why the banker locos would "tack on" to the train instead of coupling up, allowing the lead loco to maintain it's momentum.

The banker loco would typically make 3 such trips before returning to Tyne Dock to be replenished and re-manned.