Ringway 3's western section threaded its way through outer London suburbia. A line was set for this road in the 1940s, but the question of where it would run could seemingly never be settled.
Sweeping through the suburbs from east to west, the southern side of Ringway 3 would have been enormously destructive and intrusive, and yet - oddly - it was never the subject of much protest.
The Eastern Section of Ringway 3 was built and opened in its entirety: we know it as the east side of the M25. The inevitable question is: was that it?
The northern side of Ringway 3 presented few problems - that's why almost all of it exists today, and it was a bit of a struggle to not build the part that's missing.
A critically important link in London's proposed urban motorway network - but fierce opposition from the locals made the authorities scared to ever reveal its route.
This was the most controversial section of London's planned orbital motorways, and the one over which the most visceral battles were fought between planners and the public.
The east side of Ringway 2, one of London's planned orbital motorways, is a road of two halves: one still discussed today, too important to cancel and yet impossible to build, the other so straightforward that it's been open to traffic for years.
One of the oddest motorway proposals in the London Ringway plans, the Balham Loop appears to be utterly redundant. It was killed off at an incredibly early stage, and little is known beyond its route.
With its busy market, narrow shopping streets and throngs of pedestrians, Camden Town is not an ideal environment for road traffic. With Ringway 1 came a plan to provide this inner London town centre with a bypass.
The South Cross Route was the most controversial and the most destructive component of Ringway 1, London's planned inner motorway ring, but also the one for which the least information is available.
The strangest part of London's planned inner Motorway Box - not just because it's nothing like the other three sides, but also because it actually got built.
Ringway 1 would have been one of the largest inner ring roads the world had ever seen: an urban motorway encircling about sixty square miles of central London, including the whole of the City, Westminster and all of the present-day Congestion Charging zone, plus almost all of its docklands and the East End.
The Greater London Council's 1960s masterwork created a vision for a new London ringed with urban motorways - and when it was published, it seemed utterly unstoppable.
The 1940s and 50s were an era of growing traffic and growing institutional panic about the state of London's roads. The suggested fixes were the precursor to London's urban motorway plans of the 60s.
A whistle-stop tour of the motor age, from the turn of the twentieth century to the present. No pedestrians, horse drawn vehicles, invalid carriages or motorcycles under 50cc please.