The second motorway from London to Birmingham, calling in at Oxford on the way, is calmer and prettier than the alternative - but caused far more problems to build.
It's one of London's most complete radial routes, but the road envisioned by sixties planners would have been bigger: perhaps a motorway, perhaps double-deck, perhaps not.
A gallery of images sent in by visitors to the site of original photos of motorways — including some impressive views of the M4 and M11 under construction.