Yup, A27 goes through the display area and also Lancing College is pretty close by as well. At either end you have the towns of Shoreham and Lancing with loads of houses. It's all a bit tight in my humble opinion when 1/2 mile away is the open sea.
This BBC picture shows the site. The runway is normally the display axis that parallels the crowd line and then for fast jets you are at least 230m from the crowd that would put you over the A27. The spectator's areas are roughly where the mown square is on the bottom right hand edge of the picture.
LJ