(29 Sep 2014, 4:06 pm)Robert wrote Because not all journeys require buses with loads of seats like a decker.
You could argue the same about Go North East's X1 or 56.
Generally speaking, I'd suggest that Go North East is good at buying vehicles with higher running costs, especially double decker vehicles, even if it sometimes cannot be justified immediately. The fact that some journeys do require the capacity of a double decker should mean that these operators should be thinking about investing into appropriate vehicles - that way, should the services grow any more (which is expected in the majority of cases with investment), they won't face capacity issues whereby certain journeys have to be duplicated.
Again, generally speaking, Arriva and Stagecoach are seemingly a lot more reluctant to do this. Despite services 16 and 20 in Sunderland justifying double deckers for a lot of journeys (even journeys at approximately 12 o'clock are so full where you can see every seat full PLUS standees), Stagecoach opted for single deckers. It's a shame, and seems really short sighted in my opinion.