England's motorways are increasingly loaded with new technology - especially those that have become Smart Motorways. All those signals, cameras and other gadgets have to be identified somehow, and it turns out there's an ingenious system designed to do just that.
Road enthusiasts love a system, of course. Discussions about the intricacies and inconsistencies of road numbering are a perennial favourite. So it will be exciting news to anyone who likes to spot a pattern and collect a full set that there's another numbering system afoot on the motorway network - one right in front of you that's almost impossible to decipher unless it's been explained to you.
A silly mistake
The location itself is based on the markerpost number, but it can't be just the markerpost number because lots of motorways start at zero and count up, so the M1 has a markerpost 53.3, and so does the M2, and the M3, and the M4... so to avoid duplicating addresses, and confusing one place with another, the markerposts have to be converted to something unique. That's where the road code comes in.
The road code is a four-digit number that is added to the full markerpost number to generate a four-digit address. The address is then unique to the system managing it. There can be duplication of addresses across the whole of the UK, but there is never duplication in the addresses managed by each Regional Control Centre.
Some roads travel through several Regional Control Centres, and some have markerposts beginning well above zero, so devising a system like this must have been a complete headache, but the road codes are cleverly arranged in such a way that no address is duplicated within a single RCC's area.
This is the full list of road codes, which includes at least one strange historical relic.
|Route||Road code||Route||Road code||Route||Road code||Route||Road code|
|M6||4000||M53||9000||M275||9000||A38(M)||3800 & 3000|
|M18||7000||M55||5000||M602||6000||A46||4600 (East Mids)|
|M20||6000||M56||8000||M606||2000||A46||8000 (West Mids)|
* There is no M600 - it's actually referring to the M6 Toll. Some Highways England computer systems don't allow for a road number as wilfully obtuse as "M6 Toll", so the dummy number M600 is used in its place.
To get a unique address for a signal, you add the road code to the full markerpost number. So if our animated MS1 signal, which appears to be at markerpost 117/5, happened to be on the A carriageway of the M5, the number on the front would be 8175 (7000 + 1175), and its full address would be SIG M5/8175A.
The final element of the system optionally allows for multiple instances of the same type of equipment sharing the same location by adding a number to the end of their address. So, for example, an overhead gantry on the M42 with three signals mounted over three traffic lanes might carry SIG M42/6212A1, SIG M42/6212A2 and SIG M42/6212A3.
We can even try it out for real if you like.
This MS4 signal was installed on the M25 between junctions 24 and 25 when it was upgraded to Smart Motorway a few years ago. The number printed on its support should be the markerpost number added to the M25's road code - which is 4000.
It's positioned roughly 100 metres before the Driver Location Sign at markerpost 145.3, so the signal itself is probably closer to 145.2. 1452 + 4000 = 5452, and sure enough that's the number on the sign.
It may be that it's enough for you to have learned that this is how the system works. (It may equally be that you stopped reading a long time ago, in which case don't worry, we'll talk about something else next time.) But if you're the sort of person who enjoys learning about a clever system like this, you will almost certainly enjoy it even more if you know it's not quite right.
The A1, you see, duplicates its markerpost numbers, and it's a particular problem in the North East. The Driver Location Signs on the A1(M) in County Durham have had to be patched with new numbers already - you can see them as you drive past - and two road codes have had to be assigned to make sure it's still possible to uniquely identify roadside equipment reporting to the North East Regional Control Centre. Some have a code of 7000 and others 9000.
So, next time you're on the motorway and want something to occupy your mind, take a look at the signals and telephones at the roadside and see if you can work out the road code. And if that bit of mental arithmetic is too simple to occupy you for long, go for a ride on the A1(M) around Darlington and see if you can work out how to fix the markerposts. It's been a problem for years and there are engineers in a control room nearby who will thank you.
We'd love to hear about other interesting systems and conventions like this - if you know of other similar topics we should cover, leave us a message in the comments section below.
What about lighting columns? These have nice long numbers on them, too. Do they follow the same system?
Slight mistake? Sign in photo is 5452. Not 5432. Driver location sign is off by 2km as well.
Interesting that the A20(M) is listed. I wonder if that is used for either the inner or outer carriageway of the M20 through Maidstone, or is not used at all, but still assigned.
Roadside emergency telephones seem to use the same system of numbering (although they exist on more roads than this list).
I could show you the wonderful world of LRP's (those little two dots you see every so often in lane 1 of a trunk road) and Network Referencing if you wish??
Hello. I've been doing motorway stuff a long time too and, unfortunately, your photo showing the MS3 is a bad one to pick.
You see, the location is clearly an ALR (All Lane Running) area which means that the signals (also known as AMIs - Advanced Motorway Indicators) that are on the gantry in the background will always show mandatory signals. The MS3 in the foreground can only show advisory signals i.e. they have amber lanterns rather than a red ring. You don't mix the two so the MS3 will never show a signal aspect, only text. It's a 'strategic' sign which will be used primarily by the NTOC (National Traffic Operations Centre) in Quinton to tell you about problems you might encounter a few miles away...
Sorry to be pedantic. ;)