There's no reason why they can't have both if they can get the funding.

I just don't see where traffic will come from to populate this. If you've come from Durham you've better options (train) and if you are driving why would you stop when in sight of the City Centre and turn off to a car park to sit on a 21 which will take around half an hour at peak?!

I've been driving in and around the area lately and with Saltwell Rd, Old Durham etc there are plenty of alternatives available to avoid the A1 and make a decent journey time.