Yes, I get what you mean about every 15 minutes but due to the nature of the route, they could surely make an exception. It's popular enough to be getting new buses. and if ANE had a batch of 20 Sapphire E400's, then they could easily operate them on a rota basis so that they all get their fair share of hammering on the X18 and time to simmer slightly on the X21 and X22.
So it would be 4 units like this on the X18:
-Monday = 7528 to 7533
-Tuesday = 7523 to 7528
- Wednesday = 7518 to 7523
- Thursday = 7514 to 7518 and 7533
Then the rota would come around every 4 days like that.
RE: Arriva North East - Latest