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
It all started when we published an article called Mixed Signals last year, which looked in detail at the development of electronic signs through the 1960s, culminating in the Motorway Signal (or MS1). The article included an animation showing an MS1 signal in operation, cycling through some of its messages and showing off its exciting amber lights.
There's nothing wrong with the signal animation, but it turns out there was something wrong with the drawing. We were contacted by a nice man called John who has worked on motorway signalling for the last twenty years and these days works on Smart Motorway schemes. He pointed out that we'd given our MS1 a markerpost number - 117/5 - not a signal number. You can tell straight away because it's not formatted correctly, and most importantly it hasn't got a road code.
So, of course, we asked the question anyone would ask.
What's a road code?
The short answer is that it's used to make a unique address for a roadside asset. The long answer is... longer.
How to properly address a signal
We'll get to road codes and numbers again in a moment, but first we should talk about the Highways Agency Traffic Management System, or HATMS, which is used by seven Regional Control Centres. The system they use to run the technology on motorways has a number of sub-systems. Each is given a three-letter code. Here are some of them:
- SIG for SIGnals, which operates single-symbol panels like the MS1 above
- MSS for the Message Sign Subsystem, which runs bigger signals that carry several lines of text
- MID for Motorway Incident Detection and Automatic Signalling, or MIDAS, which detects traffic flow and can set signals automatically in some places
- MET for METeorological equipment: the small weather stations at the roadside that detect wind, fog and so on
- HSM for Hard Shoulder Management systems
- TID for the TIDal flow system on the A38(M) in Birmingham
Different types of equipment connected to the HATMS system are therefore identified by having different letter codes, and two items of equipment at the same location are easily distinguished. (They are not normally written on the equipment for the obvious reason that when you're standing in front of it you can tell a weather station from a motorway signal, and if you can't you probably shouldn't be sent out to fix them.) Some equipment contains more than one type of signal - for example, an MS3 signal actually contains both SIG and MSS equipment, which can be addressed separately.
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?
This is a very good question and the answer is that I don't know! Does anyone else?
No, lighting columns are not treated as operational technology by Highways England.
Instead they have an asset reference number/ID. These can take many forms from simple consecutive numbers, to reference to a local area, or even circuits/phase on a local feeder pillar.
Slight mistake? Sign in photo is 5452. Not 5432. Driver location sign is off by 2km as well.
Oops! Thank you - I must have gone number blind by that point. Fixed now.
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.
A20(M) was assigned (in the technology control data at least), to the area around the Roundhill tunnel and the signals/phones on the A20 to the south/east of it.
I have just checked the data in the SE RCC, and references to A20M were removed in 2007 and changed to A20
The A20(M) code reference still remains in HE documents for the road IDs, if it will ever be used again is another question!
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. ;)
Very helpful for me as someone who has trawled through the motorways and major A road finding these manually, though I disagree with your road code of the M69.
Most gantries and equipment are in the 8000 range, but the motorway starts with a marker post of 99/6 (approx). An emergency telephone can be found at 99/8 on both carriageways with the number 7998A/B. Therefore the road code is 7000.
I also have a query on the road numbers being unique within RCC regions, for example, the M27 and A329 both have the road code of 9000 but would also both be controlled by the SE RCC in Godstone.
The list of road codes in this article is the one I was sent - checking every single one against actual roadside furniture in case there were errors is not something I thought to do!
There's no issue with two roads within the same region having the same road code. The point of the road code is to make the resulting asset numbers unique. 9000 is simply a number that can be added to markerpost numbers on both the M27 and A329(M) without the resulting identifiers having any overlap.
I would also disagree with your numbering of the M18. The marker posts are inherited from the M1 and thus they're all up above 200km, therefore the road code is 5000.
Similar story for the M48, the road code is 1000, but the marker posts are inherited from the M4.
The road code for the M67 is 8400, the gntry just before J1A Eastbound is numbered 8422A, at 2/2, 8422 - 22 is 8400.
The road code for the A627(M) is 6200, for example the gantry at 1/6 on the B carriageway is numbered 6216B, 6216 - 16 is 6200.
Also the road code for the M181 is 1800, makes sense if you ask me
Though it does makes me wonder why the M180 doesn't have 1800 and then the M181 could have 1810 or 8100.