The M1 is Britain's first full-length motorway and possibly its most iconic. (The Preston Bypass was the first, of course, but was not very long. It was part of the M6.) It is also one of the most important, forming the main road north from London, serving the industrial East Midlands and the most populous areas of Yorkshire before handing the north-south baton to the A1(M) near Leeds. It's part of the route from London and the south east to the West Midlands, Lancashire and Scotland. It does everything, in other words, short of making the tea.
Its first section ran from St Albans to Rugby and opened in December 1959. At the time it was stunning - the idea of a road on which you could maintain breakneck speeds (and with no speed limit), that gave you three full traffic lanes for fifty miles or more, that had flyovers and bridges to get all cross-traffic and other obstructions out of the way - well, it was unbelievable. Its architecture and bridges reflect its futuristic ambition, and those that survive from that era - designed by Owen Williams, who also created the iconic Twin Towers at the old Wembley stadium - are just as striking and unique as they were fifty years ago.
Today, it has seen a number of expensive upgrades to help it cope with modern traffic. Its original specification called for road that would carry 13,000 to 14,000 vehicles per day; today it carries 130,000 to 140,000. Widening and junction improvements between the M25 and Luton make the section closes to London more bearable, but sadly those changes meant destroying the highly unusual architecture of the original motorway. North of there, as far as Milton Keynes, it's been turned into a Smart Motorway, which isn't quite so good for capacity but has allowed Owen Williams' bridges to survive.
The M1 was mostly completed in the sixties, with a continuous road from London to Leeds finished by October 1968. There were plans to extend north, passing west of Leeds to meet the A1 at Dishforth, which were shelved in the 1970s. The problem of getting traffic north beyond Leeds remained, however, and in 1999 about eight miles of new motorway were tacked on to the top of the M1 to make it swing east of Leeds and connect to the A1(M) at Hook Moor.