(27 Oct 2018, 9:45 pm)JM03 wrote Why would they operate it from a depot so far away

In the morning the 168 starts from East Rainton
Distance from CLS Depot - 5.6 Miles
Distance from PLE Depot - 8 Miles

On the evening the last trip terminates at Hetton Le Hole Interchange
Distance from CLS Depot - 7.2 Miles
Distance from PLE Depot - 6.3 Miles

Total Dead Mileage
CLS - 12.8
PLE - 14.3

There isn't actually much distance between the 2 depots and considering the time the service operates and runs, they could tag say a work service from Rainton Bridge to Peterlee on the end to eradicate the dead mileage. Plus the costs of supplying drivers for the service will be lower at Peterlee so it negates the 1.5 mile difference. I'm sure there are plenty of other routes that have much more dead mileage than the 168.

Distances provided by Google Maps.