Maybe the 6 could be reduced to every 15 minutes?

This would then allow for a more consistent service to Hollymoor and Cockfield. As at present you have a service at 35 and 00 which isn't very consistent.
So you could have a service every 30 minutes to Cockfield, and a service every 15 minutes to Bishop Auckland. Then you would have the Cockfield ones extended to Newcastle, serving University Hospital, Chester-le-Street and then non-stop to Newcastle. For example:

Cockfield                -- 15 --  45
West Auckland:      13 28 43 58
Bishop Auckland:    36 51 06 21
Spennymoor:         50 05 20 35
New Inn:               06 21 36 51
Durham:               11 31 41 01
Chester-le-St:        -- 50  --  20
Newcastle:            -- 17  --  47 (via A1)