Best way to do it is..
Upgrade the X21 with New Buses but buy more to launch the X46 and make it fall under a new brand for both routes.
X21: Every 30 mins ( 15 at peak times with peak times terminating at Durham ) New buses with Wifi, Plug Sockets, USB and next stop announcements.
X46: Every 30 mins ( 30 mins to Crook and every 60 mins to Stanhope )and the same for the buses as above.
The new brand should be like how Coast and Country follows the Coast And Country trail.
So I suggest North Pennine Connection, as Crook and Stanhope are located on the very east of the Pennine Hills and it sounds similar to Coast And Country.
RE: Go North East: Service Suggestions
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