Anna,
If driving north from Salisbury on the A345, passing through Amesbury, the road actually goes straight through the eastern sector of Durrington Walls.
It's very distracting, whilst in charge of quite a weight of steel, trying hard not to look at the banks and ditches, which are all too visible. They aren't as noticeable as those at Avebury, but, to the (modern) antiquarian eye, they are very obvious.
As for access, I've never tried. PeteG is probably the one to take advice from.
Best of luck, and let us all know how you get on.
Cheers,
TE.