(09 Sep 2014, 7:23 pm)DaveyBowyer wrote The only thing that I can think off with the PVR being 9 is Ashington getting more new E400's for the X21 / X22 due to it being a more demanding route with 7501 - 7509 going to Darlington for the 7.
7501-9 would be very hard to get under the Cornmill Centre Bridge in Darlington Town Centre - marked 14ft 6ins as you enter, and reduces to 14ft 3ins at the top end, 7501-9 are 14ft 6ins.