The wonderful A1

The A1 is the UK's longest numbered road and possibly its most famous. But the part within London, from St Paul's to the M25, might be the most easily overlooked. Thankfully some of Youtube's favourite transport geeks are turning their attention to it - so to mark the occasion, here are five things you might not know about the A1 in London.

Several years ago, comedian and Youtube star (and, shhh, closet roadgeek) Jay Foreman made a very funny (and very factual) video about the London Ringways which was partly based on research on CBRD. Now he's joined forces with Geoff Marshall - yes, from All The Stations and all those videos about the Underground - for a look at the A1. I've played a very small role in the research for the video and thought it was worth sharing with CBRD's readership, but obviously we aim to completely outgeek them, so before we get to the video, let's revel in the things that a funny Youtube video for a general audience wouldn't touch with a barge pole.

1: The A1 is not the Great North Road

Not within the M25, anyway. Of the 16 miles of A1 in Greater London, only three miles are on the traditional route of the Great North Road. The other 13 miles are on bypasses built at one stage or another to improve the flow of traffic and make the journey easier in one way or another. From south to north:

• Goswell Road (from St Paul's to Angel) carries the A1 parallel to the ancient route along St John Street
• Archway Road was built in the nineteenth century as a bypass for the steep hills on the Great North Road through Highgate
• Aylmer Road - and then Falloden Way, Great North Way and the whole of the road from Archway to the M25 - is part of the 1920s Barnet Bypass

The Barnet Bypass, opened in about 1928, is an incredible piece of inter-war roadbuilding, replacing at a single stroke more than 17 miles of the original A1 route through Finchley, Barnet, Potters Bar and Hatfield. It runs from Archway in North London to what is now A1(M) junction 4 at Stanborough north of Hatfield - a bypass so long and so much a part of the furniture that most people today don't realise it's a bypass at all. More on that in a moment.

2: The A1 has the most accurate maths

5: For a long time the A1 was not the A1

Or at least the Barnet Bypass wasn't. If you travelled out of London in the first half of the twentieth century, a smashing bypass existed to get you past all the tedious bits of road through everywhere from Finchley to Hatfield - but it wasn't the A1.

When the new Barnet Bypass opened in 1928 there was a policy to assign new numbers to new roads, so the A1 stayed faithful to the old Great North Road, and the new bypass was split into three parts: the utterly unmemorable A5092, the downright obscure A5093 and (for the middle section shared with the Watford Bypass) the decidedly uninspiring A5088.

In 1935, someone at the Ministry of Transport realised that this situation was a bit silly and that the Barnet Bypass should be given a number that would indicate its status as a major road in and out of London, so they renumbered it to the A555. That was certainly better, but still not what we would now consider the obvious solution.

In 1954 sense finally prevailed and - as part of a London-wide rationalisation of road numbers and signposting - the A1 finally moved on to the Barnet Bypass, where it has stayed ever since.

The A1 in motion

If the road facts have given you an appetite to explore the A1 in London more closely, you can either drive it or - much more enjoyably - you can watch the video here or on Youtube.