The numbering system (2024)

• A brief history of the numbering system
• Readers' comments on the numberingsystem
• Cones (not traffic cones!)
• The rest of the number

• Miscellaneous information
• Back to the roads page

Have you ever wondered why roads are numbered as they are? If not,maybe you should have done - there's a nice system for doing it, andunderstanding it even has some practical benefit (e.g. preventing youfrom getting lost).

We'll restrict our attention to the roads in the United Kingdom,except those in Northern Ireland, which have aseparate numberingsystem (but not separate enough: their numbers overlap with thenumbers used in Great Britain, and even with each other), and those onthe Isle of Man. Ithardly seems worth having a different numbering system for an area as small asthe Isle of Man, but there is one, and again, it overlaps with the numbering system used forroads on the mainland (although there are no motorways).

The basic idea is that most roads in England and Wales begin withnumbers 1, 2, 3, 4, 5 and 6, with London as the hub, and most roads inScotland begin with numbers 7, 8 and 9, with Edinburgh as the hub.There are three basic types of numbered road: motorways (beginningwith an M), A-roads and B-roads. There is actually a fairly rigorousdefinition of ``motorway'', although I'm not sure exactly what itis - perhaps I should consult the highway code? There are alsosections of A-road, such as the A1(M), which have motorwayrestrictions on them, although these do not need to have numberedjunctions (which motorways do). These restrictions ban, among otherthings, pedestrians, animals, small motorcycles, domus, humus and rus.[Surely some mistake - Ed.]

One might have thought that the first-built road would be numbered 1,the second numbered 2, and so on, but it doesn't work like that,although admittedly the A1 is one of the oldest roads, being reputedly two thousand years old! (Legend has itthat it started with someone walking from Edinburgh to London.) Noattempt is made to use all the numbers: for example, there is no M7,although after reading this, you'll be able to guess where it would beif it existed. Instead, the number of the road should be thought of asa sequence of formal symbols (such as letters)which just happen to look like numbers. So,for example, the roads which begin with 1 are more closely related toeach other than to roads which begin with 2, just as words beginningwith A are grouped together in a dictionary.

A brief history of the numbering system

By James Bufford

With the rise in road traffic at the beginning of the 20th Century and theneed to provide government funding to improve them, the British governmentstarted work on classifying the road system. The First World War interruptedwork but it resumed afterwards and in 1919 an Act of Parliament was passedwhich gave the OK for the Government to fund roads and, in order to do so,they decided to number them.

It was fairly quickly realised that a numbering system would alsobe useful for navigation. The newly created Ministry of Transport (MOT) setabout identifying which roads needed funding, and numbering them. There wereto be two classes of roads: A roads, more important with more funding,and B roads of lesser importance.

By 1921 the MOT had identified the system for England and classified 97 mainA roads, with one or two digit numbers - some of these were published onMichelin and Bartholomews maps, much to the Ministry's irritation - and toBartholomew's irritation as some of the numbers then changed.

The formal classification was not published until 1923, in a little bookletpublished by HMSO. The Ordnance Survey published a series of maps - the MOTseries and several other mapmakers published revised road maps. Road numbersalso went up on signs.

Numbers changed quite a bit in the 1920s:

On the subject of numbering, this is something which used to fascinate me as a boy when my dad, noting my early interest in his road atlas, explained the UK system of numbering roads to me. On long journeys I would often try to find exceptions to the general rules. The A41 was a favourite of mine (the London to Birkenhead (!) trunk road). Whilst the southern half appeared to justify the 4 numbering (being largely south of the A5), it then crosses the A5 north of Wolverhampton and continues merrily northwards. But even if the logic was that the road ``starts'' in London, it starts to the``right'' of the A5, and terminates to the ``right'' of the A5, so cannot really justify being in the 4 zone. Interestingly, it runs exactly parallel to the A5 for its first 15 miles from London, and crosses the A5 twice on its way north. Furthermore, in this first leg, it also gets eaten up by the A1 for a short length, which must be a unique achievement for a north-south running 4 road. A further point of interest is the absence of the A6 in the north London area - did the A6 ever reach the capital? It currently ends at Luton, and the oldest map I have shows it ending at the South Mimms junction with the A1 (pre-M25). Presumably it followed the now A1081 through Barnet, but must have then run into the A1 again well north of The City. Thus, we have, from West to East, the A5, the A41, the A1, and the (ex) A6 (in that order) all running parallel north of London - not only completely undermining the numbering system, but doing so only 5 miles after leaving London.

And don't start me on the M54 (all of it south of the A5), or the M62 (starts in zone 5, finishes in 1).

I also wonder what number the new Birmingham Relief Road will get - running virtually alongside the A5, and will it actually get an ``M'' allocation, as Britain's first toll motorway? Any thoughts?

Cones

The basic criterion determining the first digit in a road's number iswhich ``cone'' (or zone) the road begins in. The cones are numbered 1-6 (forEngland and Wales) and 7-9 (for Scotland), and are basically definedin terms of the nine key roads A1 to A9 (which do all exist).Roads in England are generally considered to begin from the Londonend, and roads in Scotland from the Edinburgh end. When the road hasnumbered junctions (usually because it is a motorway, although thereare exceptions, like the relatively new A14), the low-numberedjunctions are at the beginning of the road.

As I mentioned, the roads A1 to A6 are considered to start fromLondon. They emerge clockwise starting from the north: the A1 goes toEdinburgh, the A2 to Dover, the A3 to Portsmouth, the A4 goes westto Bristol, the A5 to Holyhead and the A6 to Carlisle. (Note thatsome of these roads are no longer continuous, since sections of themhave been replaced by more major roads: for example, one section ofthe A5 near London was renumbered, presumably to confuse people intousing the M1 instead.) The 1-cone, where the roads begin with 1, liesto the north of London between the A1 and the A2, and so on, endingwith the 5-cone between the A5 and the A6, and the 6-cone between theA6 and the A1.

Numbering in Scotland works analogously. The key roads, which emergeclockwise from Edinburgh, are the A7, which goes southwest toCarlisle, the A8, admittedly largely eaten up by the M8, which goeswest to Greenock, and the A9 which goes north to Thurso.

This basic plan applies to all the types of road, notjust A-roads. However, there are some exceptions, some of themirritating. One of the most striking is the M5. It is usually thecase that if a motorway and an A-road have the same number (e.g. theA3 and the M3), then they go approximately in the same direction.However, the M5 is a blatant exception: it goes from Birmingham toExeter and is clearly very friendly with the A38, which it isessentially replacing throughout its length, so it should be calledthe M38. The A5, in contrast, is almost at right-angles to the M5!

Charles Walkden's numbering game, and other numerological pursuits

The M621 (Leeds to Gildersome) in avery real sense joins to M62 to the M1. How many othermotorways/A-roads are there for which there exists a partition of theroad number into the two roads that it connects?

Of course the M62itself fails, for it does not join the M6 to the M2. Nor do I countthe trivial partition: the M25 should not be regarded as connectingthe M25 to the M25, nor should the M6 be regarded as connecting the M6to nothing (although this probably depends on your opinion ofCarlisle).

Well the A46 (which runs right near my house) joins the A4 at Bath to theA6 at Leicester.

Also the A404 (a very strange road which loops round a full semi-circle)runs from the M4 near Maidenhead, across the A4, across the M40 and theA40 at High Wycombe then round and into London where it joins the A40(M)so it joins its partitions in both the motorway and the A road sense!

Yes, there is another one! The A1214 in Ipswich connects the A14 to thesouth of the town (where at an interchange it begins multiplexing with theA12 east, and eventually northbound) with the A12 to the east of the town.Exiting the A14 into Ipswich at the Copdock interchange, you travel on theA1214 northward, through the north of the town, through Kesgrave and outonto the A12 at Martlesham.

Interesting numerical coincidence: Until the A604 was re-designatedA14, I couldn't think of any junction which gave access to a road ofthe same number as the junction; now I can think of two: M11 J14 isfor the A14, and A1(M) J14 is also for the A14.

And another one... M32 J3 joins with the A4320 (which is a relief road to link the end of the motorway to the A4 Bath Road and thus avoid the Bristol inner relief road and city centre). Along its length (about 2 miles) the A4320 has junctions with the M32, A432, A420 and A4. I just wonder if the bods that named the road knew what they were doing and called it the A4320 on purpose just for this very reason.

The A939 - the infamous co*ckbridge to Tomintoul road in Aberdeenshire - has a lesser sibling the B939 in Fife between Craigrothie and St Andrews. Are there any other cases where a road number gets used for different classes of road that were never part of the same road? (Well, I can't see how these could ever have been connected.)

Cone anomalies

Is there any system for the allocation of numbers ofroads such as the A46 which cross several ``cones''? Why for example isthe A46 not the A1xxx as its northerly point at Grimsby) is east of theA1. (I see that it appears to start at the A4 in Bath - and wonder whythere should be a route between Grimsby and Bath.)

The A100 and B300 are very short roads in central London,each not much more than 1 mile.The B709 by contrast is a long road which starts about 8 miles south ofEdinburgh and ends at Dumfries - a distance of some 50+ miles. Doesanyone know of a longer B road?

Stephen Bott answers:

I think the B1145 is one of the longest B roads in thecountry too. If you look, it goes from Kings Lynn toMundesley (near Cromer).

Surely the M25 is an anomaly to the cone system and ought to be the M0 or perhaps just the M?

The M4 ran across the old Severn Bridge but when the new bridge was built, the new section linking the new bridge to the old road was called M4 and the part excised by this is now the M48. Are there any other examples of M sections being renumbered? [Yes: have a look atthe M60 fiasco for a good example! - Ed.]

I cannot see what is wrong with the M25 being numbered as it is. Yes it doesnot fit into the cone system, but it does run alongside the road itreplaced, the A25. Surely this is a good enough reason for the number. Itcan hardly be called the M414 (the road it runs alongside in the north).Also in a more gentle time, the A25 used to be known as the valley road.

If the two-digit A-roads (12, 57 etc) were originally built astrunk roads crossing large distances (which they were), where on earthdoes the A38 come into things?! It runs from Bodmin (Cornwall) toMansfield (S. Yorks) by way of Plymouth, Bristol, Birmingham and Derby.The M5 replaced most of it (so surely that should be the M38) but it'sstill there.

This is incorrect. The A38 does indeed terminate at Mansfield but Mansfield is nowhere near South Yorkshire as it is well and truly in the county of Nottinghamshire.

Roads entirely in the wrong cone

As far as I can tell, the A3400 starts at J4 of the M42 andends where it meets theA44 near Chipping Norton. Thus, despite being numbered as an A3xxx road,its entire length is within the 4 cone of the road numbering system andhence it should definitely have a number beginning with 4 rather than 3.

I wonder if there are any other roads which run entirely outside the conethat their number suggests that they belong in ?

This is probably because the A3400 follows part of the course of the old A34 (hence the name). Furthermore, it must have started in the 3-zone: even if most of it lies in the 4-zone, as long as it starts in the 3s it's okay numberwise. I guess the part within the 3-zone has been downgraded thus giving rising to the apparent anomaly. This is all guesswork, by the way. There are, however, two examples in London that people often bring up. Firstly the A41 which starts east of the A1, i.e. in the 1-zone. Its route was revised many decades ago but it originally started west of the A1, i.e. in the 4-zone. Secondly, the A6, which appears to start in Luton, a mere thirty miles from London. The present A1081 was the A6 a long time ago, so that's that one wrapped up.

Paul just slightly misses my point on the A3400's uniqueness, because although there are several examples of roads which run for very little of their length in their numerical ``home cone'', the A3400 is, as far as I know, the only A- (or for that matter B-) road which runs entirely outside its ``home cone''. I accept the A3400 may, at one time, have run for some of its length (now renumbered or declassified) in the 3 cone but, if so, I can't find any of it in there now and I think this still makes the A3400 unique as things stand. (Different rules, of course, apply to Motorway and C-road numbers.)

Please let me know if you know of any other such anomalies (or, alternatively, if you can confirm that the A3400 is unique in this respect).

I am now able to answer my own question. There is atleast one other A-road that runs entirely outside its ``home cone''. Thisis the A6144 which - along with its sibling, the notorious A6144(M) - runsentirely within cone 5.

The A3400 is NOT unique. The A4601 also never enters its home cone.It was formed when the A460 was re-routed along the Cannock easternbypass, and is the result of the original route renumbering. It'sfrom the A3400 school of renumbering. Whilst it does start at theA5, it then goes the wrong way (northwards) away from it throughCannock Town Centre, and finally ends up back on the A460 in Hednesford.

We've been discussing this on SABRE in a thread entitled "Roads entirely inthe wrong zone", and the answer is definitely yes! Including the A3400,we've now got fifteen entries:

• A3023
• A3400
• A42
• A427
• A4601
• A6144 (And A6144(M))
• A8000
• A88
• B316
• B325
• B4666
• B4667
• B4668
• B4669
• B5444 (Swansea version - as Julian Dommett points out on your site, there'sanother one in Mold!)

Some of these are due to truncation, some to rerouting of zone boundaries,some are deliberate attempts to create a distinctive number, and some appearto have no explanation at all - they're just careless renumberings. Hopethis helps!

I understand you have been in touch with Swansea City Council about theroute number of the above mentioned road.

The classificaton of highways and route numbering, where appropriate, inWales is the responsibility of the National Assembly for Wales, andformerly the Welsh Office. Pentrechwyth/Jersey Road was allocated a classifiedroad status in 1991 and given the number B5444 due to the construction of thePentrechwyth bypass and cross valley link.

Unfortunately the route number used was not appropritate for use in SouthWales, all roads in this area would normally start with the number 4.Also, as you have pointed out, the number was already in use on road in theMold area. We will be discussing an amendment to the route number with theCity Council and once agreed we will inform the map production companies. TheCity Council will then amend the necessary traffic signs.

Thank you for making us aware of the error.

The rest of the number

So, that's the first digit of the number explained? What about therest of the number, you may wonder. The rules for determining thesubsequent numbers are necessarily more vague, since not all roadslead to Rome (respectively, London or Edinburgh), but the idea is thatthe closer to the hub the road starts, the lower the secondnumber should be. The secondary numbers also tend to sweep clockwiseround the cone in the same order as the primary numbers. This iswell-illustrated by the roads A20 to A24, which essentially start inLondon. The A20 goes south-east to Folkestone, and the Channeltunnel.The A21 goes to Hastings, which is further to the west; theother roads occur in sequence passing to the west: the A22 goes toEastbourne, the A23 to Brighton and the A24 to Worthing.

Motorways and B-roads are qualified in a vaguely similar way. Themain difference is the number of extra digits which may be added.Motorways usually only have one or two digits, but a few (like theM180) have three. A-roads may have one, two, three or four digits,even if they have motorway restrictions (like the A6144(M) near Manchester).B-roads have three or four digits. The length of a road's numbertends to be in inverse proportion to its importance.

One of the high points of my recent honeymoon in the Outer Hebrides was my first sighting of a road sign bearing the number of a classified `C' road: I hadn't known such things existed. It was in the middle of Tarbert on the Isle of Harris, and I was so interested that I took a photo of it! My wife was rather dismissive, suggesting that such things were common in the wastes of Scotland.

It was the C78 to Kyles Scalpay. Rather like most of the back roads on Harris: single track with passing places, rough-edged, tortuously winding... I presume it merited a number because of being the road to the Scalpay ferry, and hence in local terms a ``trunk''route, but could not in all honesty be classified as a B road. I think they may be building a bridge to Scalpay now, so maybe they'll upgrade the road too.

You might be interested to know that Jersey has an extensive network of C-roads. The map there lists A and B roads (coded green and red, not sure which is which) and yellow C-roads, no Motorways!

There is also a classified C-road running from Lovedean towardsHaslemere, I believe. However, since it has been some years since Iwas there, it is quite possible that I am mistaken as to the origin,the destination and the classification.

Re Matthew Garrett's comment: C roads are still used by Waverley BoroughCouncil (which includes Haslemere). They're published in the paper onpublic notices for roadworks, like the junction of the C1234 (HighStreet) and C5678 (Station Road) will be closed for X days (fictitiousnumbers and places). I think I remember some D roads as well, but couldbe mistaken.

There are a couple of C-road numbers on road signs on mini-roundabouts on the Southern edge of High Wycombe - somewhere near the arrow on here

I believe that the C-road classification was formerly available for useby County Councils to allow them to identify roads not otehrwisenumbered, but regarded as having particular local significance. Myrecollection is that there was correspondence on this subject in the CTCGazette (the magazine of the Cyclists' Touring Club) sometime in the1950s (but possibly in the 1980s). The use of the classification wasoptional.

Sc*nthorpe also has 'C' grade road (its number I can't remember off thetop of my head) as well as a road sign that tells you to drive on the righthand side of the road. Very odd, and the only one I've ever seen.

About 1 mile outside Holmfirth on the B6106 (Dunford Road), thereis a modern road sign indicating, to the left C577 (and if you go about a mile down that road turning left, you come to a place called Paris).

I've also seen roads with "R" numbers (on roadworksadvance-notice signs). Are these for Rural roads that don't haveCounty numbers?