But the Dft Card Index has an entry for it: "Reserved for Bristol Road". This is vague and unhelpful - does it mean a road called Bristol Road somewhere, or is it for a road in Bristol? The capitalisation I would tend to ignore, there are so many spelling and other errors that it's likely to be just another one of those.
But A440 is still waiting to spring back into existence. Has anyone ever heard of a "Bristol Road", or Bristol road plan that would reuse the number?
I'd say "answers on a postcard", but a postcard is all the evidence we have so far.

By way of contrast, A434 also has an entry on the index, but it is blank.