(06 Jan 2020, 6:12 pm)Andreos1 wrote I wouldn't say they were particularly narrow, although the 57 does get down some estate roads.
Some of the route of the 57A is shadowed by the X21 and you know what gets allocated to that.
I'd suggest the vehicle allocation for the 57a was more to do with loadings than owt else.

Yes, Service 57/57A it is specifically allocated Solos, mainly due to the route in Quarrington Hill.

It Interworks with half of Service 43, presumably to allow driving duties to be cut in either, 3, 4 or 5 hour chunks. If the 57/57A didn't interwork, drivers would need to be changed every time, creating only 3 hour chunks of work, which isn't very efficient.