(09 Aug 2015, 1:10 pm)Davie wrote No. I think it interworks with service X9 Mondays - Saturdays.
Doesn't look like they do interwork unless (and quite understandably), there is a long layover at each end.
For example, an X10 leaves Newcastle at 11:00 and will get to Middlesbrough at 12:20. The next X10 out of Middlesbrough is at 12:30 meaning that it would be the next bus out and would get back to Newcastle at 13:50 . The cycle would keep going and works in the same way for the X9.
As i say, with it being such a demanding route for drivers, they may be given 40 minutes layover at each end allowing buses to alternate between the two routes.