Chugalug,
It would seem that we got out of Thorney just in time (for I was short-toured and away in early '60), and so our idyll on the Hampshire Riviera was not ended by those big, noisy, dangerous things of yours ! (Let's hear it for the Admirals). Interesting too, that the A23 went as far as LGW, for it was also the coast road where I had my duel with death on the runaway bike !
'Tis all too true that motor vehicles and aircraft do not mix at all well (or MVs with one another come to that, as a horror story - coming shortly - will attest). As you say, complete separation is the answer, but apt to be expensive. I am sorry about the Mole River (that surely must be the one where the immortal "Ratty", Mole and their friends live), but I suppose it'll have to take its chance in the scheme of things.
All forms of barrier fail in the face of the old adage: "There is no such thing as a foolproof system - you only breed a new kind of fool".
Danny.