As I was putting down the track today, I changed the design slightly as I thought my runaround loop was too small. I added a small loco stabling/ re-fueling point as well as changing the runaround loop.
After arriving, the loco can either propel it's train back into the tunnel, and run around it's train in the fiddle yard, or, if the fiddle yard is full, a station pilot, probably a 141, will release the loco. The loco can shunt in the freight yard or refuel