(06 Jan 2020, 5:30 pm)S830OFT wrote The 57/57A have been fully Optare Solo operated today. By any chance is there any narrow roads on the 57 route?

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.