Where are they, between J16 and North Stoke? Google maps location please
I tend to go to J15 and then A500 and almost straight onto the A50, but its worth knowing the van location for the future as it is tempting to break the limit on that stretch before you reach the 50 section in town.
On the A500 between the A34 and A527 (Southbound) exits....

http://maps.google.co.uk/maps?f=q&s...3.053313,-2.216191&spn=0.018573,0.038581&z=15

