Everyone knows the M1: it's the original long-distance superhighway, the iconic route north from London, serving the Midlands and Yorkshire. Arguably, this is the dull one of the set, because there is little to add from a historical point of view. What was built is almost entirely what was intended, even if the GLC did like to refer to it, in the manner of just another unbuilt plan, as the "Luton Radial".
The difference is (as ever with the radial routes) at the London end of the motorway. While the M1 comes much closer to central London than most existing motorway routes, it is still missing the last couple of miles of tarmac that would have taken it to its intended conclusion.
Continues towards St Albans and the North
R4 North Orbital Road
R3 Northern Section
Local connections to Edgware & Stanmore
Stirling Corner Link to A1
Local connections to Hendon
R2 North Circular Road
R1 North Cross Route
The M1 planned back in the 1950s and 60s is much as you see it today: entering from the north via Luton and St Albans, it would have crossed Ringway 4 somewhere close to the existing junction 6. The present-day M25 at junction 6a was not part of the plan, and is actually an invention of the 1980s designed to bolt parts of Ringway 3 and 4 together with the minimum damage to the suburbs of Watford.
The M1 would continue south, interchanging with Ringway 3 near Bushey, about half-way between junctions 4 and 5. Its continuation south-east would take it to Scratchwood Services and the Stirling Corner Link, a spur connecting it to the A1 to the north. This was never built, but the access to what is now London Gateway Services uses the incomplete junction 3.
The motorway then would meet Ringway 2 (today the A406 North Circular Road) at Staples Corner. The junction that stands there today is clearly intended for the M1 to pass straight through and continue south, with the North Circular lifted high above the interchange to allow the M1 to pass between it and the roundabout on its journey towards central London (shown left).
From there the motorway would have continued to follow the east side of the Midland Mainline railway, terminating on the Ringway 1 North Cross Route at a complex free-flowing interchange near Brondesbury Station.
The most interesting thing about the M1 is the provision left for its extension to the North Cross Route. Room for future extensions are nothing exceptional in the Ringway plans (or, indeed, for the rest of the British road network), but this is a special case. The M1's approach to the A406 North Circular Road opened in 1977, some five years after the GLC had been forced to cancel large parts of the Ringway plan, and Ringway 1 had been thrown out by both the Treasury and the Cabinet. There was room for the M1 to continue, but nowhere for it to go.
So why, five years after its destination was permanently cancelled, would the M1 still be built with space for its southern extension? There are a couple of theories, both plausible and based on similar situations elsewhere. The first is that the interchange with the A406 had been planned when the southern extension was still likely to go ahead, and when the scheme was ready to start construction, it was too late or too expensive to begin re-designing the interchange. It is known that the A406 high-level flyover already existed so perhaps the current solution was thought to be the easiest way to connect the M1 to the existing roads.
That doesn't quiet work, though, because the enormous carriageway stubs - ski jumps, to use the jargon - were built for the M1's mainline. Even if the plans weren't being changed, it would surely be possible to omit these monstrous features, yet they were built. The second possibility is that an extension of some sort was still on the cards, and it seems that for a time in the 1970s and even the 1980s, there were proposals to extend the M1 southwards through Hampstead and Willesden Junction to reach the stub of Ringway 1's West Cross Route. This would relieve the congested A41 through Finchley, by allowing traffic bound for Central London to use the A40(M) Westway instead; it would also tie the motorway in to the proposed Western Environmental Improvement Route, a late-70s resurrection of the West Cross Route to be built at a lower standard.
Either way, the extension never happened, and the white elephant interchange at Staples Corner was made slightly better in the 1990s with the addition of a short-cut flyover from the roundabout to the M1, making use of some of the empty space that the motorway was supposed to pass through.