Would anyone agree that the Sunderland to Concord section is used less than the Concord to Newcastle section of the 56 service?
How's about a service every 20 minutes between Sunderland and Newcastle, but every 10 between Concord and Newcastle? The short and long 56s would interwork at Newcastle, and would provide a PVR of 12.
If we were to suggest that the 56 was to receive 17 new B9s and the 309/310 was to also receive 17 new B9s, the remaining 5 vehicles for the 56 could be used for an X56 service (feel free to send in your suggestions for this one!) requiring 4 vehicles, while 1 acts as a spare.