I hope this question isn't as silly as it sounds - what I'm getting at is this.

Junction 1 of the A1(M) is at the start of the southernmost section where it meets the M25.

Most, if not all, of the other long-distance motorways radiating from London extend further into town than the A1(M) and the junction numbering reflects this, or they were once expected to penetrate further into London and the numbering allows for this, even if the inner section didn't get built.

In the case of the A1(M), however, although there is a DC corridor for A1 that extends well within the M25, the numbering still starts at 1 on the M25.

Now I can see that there might be a number of explanations for this. For example, you could argue that the A1(M) was seen as a number of discrete bypasses rather than being seen as a long distance route that would be extended further into London - but on the other hand, the junction numbering of A1(M) treats the A1 route as a whole, at least as far as Newcastle, and implicitly extends the numbering to sections that aren't (yet?) motorway - so why not south of the M25?

A1(M) is also pretty old, so it's not as though work on A1(M) started only after it was held to be unrealistic to extend motorway routes as far into London as had previously been expected. On the other hand, that may have been the case by the time a comprehensive numbering system for A1(M) junctions was devised, many years after the initial sections of A1(M) was built. Any thoughts?

When the A1(M) was built junctions were unnumbered. By the time numbering took place (late 80's) urban motorway building was dead.

Motorway junction numbers were invented about 1965-6 (anyone know the exact date?) but several shorter motorways and An(M) motorways were originally left out.

I think the Yorkshire and Tyne-Tees sections of A1(M) were even later getting them than the Herts section.

You'd have though that it, possibly might be J3, taking it to Stirling Corner link road. J1 and 2 would have been mostly in Greater London, rather than Herts, which is a good reason to look at as to South Mimms is J1.

AFAICS, other than the Possible North London Radial (which might not have been motorway), there was no plans by London in extending it further south - the Scratchwood Link would have been to an all purpose A1.

M20 is the same, and M3 and M40 don't get that far inside the M25 before coming to an end.
Remember that in some cases, when the radial motorway was built, plans for an orbital motorway were still hazy at best, so they wouldn't have known exactly where it was going to go. That's why M1, M4 and M40 all have suffixed junction numbers.

I think you've answered your own question there - it's the HQDC that gives the game away. The motorways where the numbering starts at '1' quite some way out - A1(M), M3, M20, M40 - have good DC links in towards the capital, so there was no need for the motorway to be extended further. The routes where the numbers start higher, leaving potential for more junctions to be added - M11, M23 - are missing that high quality link, so when they were built, it was hoped that they would be extended.

Not quite - all of the above suffer from the M25 moving from the quite clearly defined Ringway 3/4 plans. The M1 meets the "Watford bodge", the M40 would have met R4 (and the Denham Spur) at Denham roundabout, and the M4 is just a cock-up as the junction is in exactly the right place. I have seen maps of the M4 with the junction numbers all shuffled down one - M25 being J5, Huntercombe being 8 and the present 8/9 being just 9.

Now that soulds like far too a sensible idea to be implemented. - Although given that it has been as it is for so long, the costs in making the change would be pretty high for all concerned.

Go pro road and re-instate the ringways project i say, get the bulldozers in

Don't know the exact date, you are round the right time, but one of those who put the plan together came to talk with us at university in the early 1970s, and described the process. I may have written about this here earlier.

One senior guy had the whole idea conceptually, the project was approved, the adaptations of signing were devised, and the detailed scheme of numbering everything was done for all motorways, present and proposed.

The numbering started right from Central London, and was done in miles. So the M4 would start at Chiswick at J7, Brentford J8, Heston Services (they numbered the services as well) J12, Heston J13, Heathrow J16, etc. This gave an indication of distance, allowed for new junctions, etc.

All prepared, put up to the Minister for approval. The Minister said the government should be encouraging metrication, and for a new scheme it should be metric, otherwise he might look silly to colleagues embracing the new world order. Comments about all signposts, vehicle odometers etc currently only being in miles were brushed aside.

Back to the desk, redid the whole scheme in kilometres. M4 starts at J10, Brentford J12, etc. Put up to the Minister again.

Minister (same one) said there appeared much public hostility to metrication, scheme might be ridiculed in the press, he would look silly to voters, etc. Do something different. Anything.

Back to the desk again. Someone said "do them sequentially then". And that's how it was done.

I remember that when the announcement was made that junctions would be numbered, there was an item about it on whatever the then current David Frost satirical TV programme was called (possibly BBC3, several decades before there was a real channel of that name). It was a pseudo-romantic song about key events in a couple's relationship and the places where they happened, except numbers were used instead of placenames. Something like

Do you remember the night we met
at a hundred and seventy-three

and so on.

The above information implies then that motorways such as the M1 and M5 did not have junction numbers when first opened and presumably explains why junctions on these older sections were known by names, e.g Lydiate Ash, Berrygrove etc.

Ian (M5 DRIVER)

Yes, that's right. You get road atlases from 1958 to about 1965 where the junctions are actually names on the maps.

You're thinking of "TW3" - the abbreviation of That Was The Week That Was.

I like smaller numbers and distance numbering has its own problems.

Take M8 in Glasgow - J17/18/19 would be in the same kilometre, so you'd have (hypotehtically) M8 J44A, 44B, 44C etc...

I'm not thinking of That Was The Week That Was, which was terminated in 1964 (or at the end of 1963) because an election was due in 64. It was followed, after the election, by Not so much a programme, more a way of life, which was followed by BBC3, which was followed by The Frost Report. If you've ever seen the "I look down on him" sketch with Cleese, Barker and Corbett, that was from The Frost Report.

Look again at my original post and you'll see BBC3 is a link.

I think that either the link colour, or the default text colour, or the background colour, should be changed, so that links stand out more. At one time I started underlining links in my posts but somebody didn't like it for some reason.

My apologies, I was browsing on my phone so missed it... whoops.

No, they would have been 43, 44 and 45 for such few instances. The Distance measurement doesn't have to be to a surveyor's precision, numbers can be adapted to suit.

But given the junction spacing that means that every junction along the M8 from current J6 to junction 31 (because there's too many A junctions for J30 being one higher than J29 to match it's chainage, even though the gap is bigger) would not be distance based, but actually just sequential starting from a different point (junction spacing is less than a mile on average). That's no bonus - in fact, unlike today, the junction numbers would be misinforming!

Sure, do it with M5 J15 and J16, which are 500m apart according to the chainage figures on CBRD, but with the M8 you are going to need several A junctions, if not a B junction or 2. The sequential numbering works, though perhaps some small differences would have made more sense when they did it.

Oh, and mileage-/kilometrage-based numbers will sort out how many suffixed-junctions? Under 20 on the motorway network. It's not worth it.

It's also worth thinking about the fact that the likes of M4 J4A and M23 J9A would still need suffixes...

And M11 J8a, M8 J28a and similar, given they are part of the same junction - with Stansted, you'd make J8 '8A' and 8A '8B'.

I took into account all that and guestimated - I worked it out, there's about 25 if you count the M74 and M80 ones that haven't happened yet, ignoring the M8.

You can, of course, get rid of quite a few of them if you shuffle numbers along - either move M1 J4, 5 and 6 down one, or make j6a junction 7. Likewise the 8/9 shuffle to remove J4b on the M4.

Of course, Staples Corner would become M1 J11 (if we use the marker posts), so a lot less starting at J1!

WBHM wasn't actually suggesting it should be done, just explaining the what was considered