(23 Feb 2023, 7:44 pm)Storx wrote You'd struggle with some of them as you'd have an uneven service with the 6/X21 and the 49/49A does an anti clockwise / clockwise loop which wouldn't really work.

Personally imo this would be better for the 21/X12/X21

X12/X21: Every 15 Minutes; Durham to Newcastle both via X12 route
21: Every 7.5 Minutes, Newcastle to Angel; Every 15 Minutes Angel to CLS, 30 Minutes to Durham.
21/X12/X21: Every 7.5 Minutes; CLS, Birtley to Newcastle

Would up the frequency on the core section and drop it on the quieter part (Angel to CLS) which would gain the X12/X21 at some stops - the A1 is a constant car park lately.