Metrication timeline for British road signs

In response to one of his enquiries, the UK Department for Transport (DfT) has provided Ronnie Cohen  with an account of recent progress on the introduction of metric signs on UK roads.

I recently asked how the DfT how it decides where to use metric and imperial units. The DfT responded with the general point that “For a traffic sign to be lawful, it must be either prescribed in the Traffic Signs Regulations and General Directions (TSRGD) or be authorised by the Secretary of State for Transport.”.  In its response, it also gave a metrication timeline for British road signs:

“1980: Since at least 1980, motorways have had distance marker posts installed at 100 metre intervals alongside the hard shoulder. They show the distance from a pre-defined point on the network measured in kilometres.

1981: In the TSRGD 1981, the basis of controlling the movement of heavy goods vehicles was changed from unladen weight in imperial tons to maximum gross weight in metric tonnes.

1981: In the TSRGD 1981, highway authorities were also given the option of showing metric height, width and length limits in separate signs alongside the imperial ones.

2007: Driver location signs were introduced on major highways at 500 metre intervals. They show the distance from a pre-defined point on the network measured in kilometres.

2016: In the TSRGD 2016, metric units became mandatory for all new signs showing height, width and length restrictions. They must show metres alongside feet and inches.”

This describes the progress that has been made with introducing metric units on UK road signs. Of course, the story begins much earlier, with a recommendation from the UK Metrication Board in 1970 that the changeover  to metric units on UK road signs should begin in 1973. Within a year, the Minister of Transport Industries had postponed the matter, and it was stated that “the Government had no alternative date in mind”. Since 1980, as with metrication in other areas, progress has been slow and erratic. However, progress on road signs has been even slower than in other areas of the British economy and very limited progress has been made on metrication in road transport.

British road signs remain generally imperial, leading to a common misconception that the use of metric units for distance on all signs, public and private, is illegal. Britain is probably unique in the world in prohibiting metric units for distance and speed on road traffic signs. Despite the widespread use of metric units on private signs and elsewhere in the British economy, successive governments and the DfT have remained reluctant to consider a comprehensive and orderly changeover. Today’s Queen’s Speech, setting out the current Government’s programme, is unlikely to change this.

16 thoughts on “Metrication timeline for British road signs”

  1. Perhaps the one thing the government could do, even if it continues to require distance and speed limit signs in Imperial, to explicitly allow distance signs to be metric only to clarify that anyone posting such signs can do so legally (without including Imperial).

    Speed limit signs are much more sensitive but metric-only speed limit signs could also be made legal by private entities (such as parking garages, private roads, etc.)

    Any chance this clarification could ever pass Parliament? Or could DfT just issue a new regulation?


  2. Re Daniel Jackson’s post:
    Why does Flintshire Council take any notice of silly old duffers like BWMA? Would they act if Metric Views objected to signs in imperial? Warwick Cairn’s comment amused me….”They probably think it’s the twenty first century….” It IS the twenty first century. But obviously not in Mr Cairn’s mind.


  3. I don’t think the U.K will ever complete the metric changeover, I wish I was wrong but I was taught in school years ago and here I am in my forties and still nothing. On a unrelated topic why do national newspapers still use Fahrenheit when its hot when everyone I spoke to both young and old use Celsius.


  4. @ Cliff,

    I posted this here mostly to point out that the dual use of units is a farce. If you notice, the drivers ignore the imperial and follow the metric value. The metric value in this case was wrong. The driver hit the bridge because he thought his 4 m high vehicle would pass under a 4.1 m high underside of the bridge.

    It should be noted that the article mentioning the BWMA is from the end of June this year and the other article with the corrected sign is from 2 years ago (2015-07-03). The original article on the accident was from 2015-06-19. The picture article was from the day before. It seems that this publication choose to reprint that article two years after the fact just to give print to a BWMA boast.

    The sign was changed showing a height of exactly 4.0 m and some imperial gibberish that no one refers to.

    Somehow the BWMA was able to convince them that metric only is illegal. If the government were to amend the law to make metric alone fully legal, the Flintshire Council could just as well told the BWMA to get lost.

    I’m glad you noticed Cairn’s comment. Yes a full Freudian slip. He thinks the UK should exist in one of the previous centuries, possibly the 19-th when Britannia ruled the waves. Some people just can’t get over the truth that the empire is dead and time to move on.


  5. One interesting point is the motorway/dual carriageway marker posts, I haven’t been there for a few years but last time I was in Northern Ireland I noticed that these were still placed at imperial distances (I can’t remember the distance but they are very close together).

    I can only imagine that this is like many of the laws in NI, hindered by some backward thinking groups determined to stick a finger up at the south at every opportunity.


  6. The stuck lorry at Flintshire perfectly illustrates (again!) the problem with dual measurements. If only metric units were to be used on such signs, the measurement would have been made directly in metric units and would have been correct.

    As others have pointed out in other posts, when you have two sets of units and you engage in conversion from one to the other, you are simply asking for trouble (and mistakes).

    Yet another fine example of both the virtue and necessity of scrapping Imperial and going 100% metric.


  7. There is a sign where I live in Essex saying “no hard shoulder for 9000 m”. For a while this seemed wrong because a quick mental calculation told me that 9000 m is a little less than 1 km and the distance seemed more like 5 miles. Then after a few weeks I realised that 9000 m was in fact 9 km. In imperial units this would have been expressed as 5 1/2 miles – something we all understand.


  8. @ Graham Palmer 2017-11-03 at 14:49

    Another rather strange response. Surely the first thought for someone truly Imperial orientated on seeing ‘9000 m’ would be ‘9000 miles? that’s too far!’ I must say that 9000 m is a rather strange way of signposting but this is another oddball trait of this country. It seems (my perception of the media in UK) that umpteen – thousand metres is an acceptable metric statement, but using those dreaded kilometres seems to remain a media taboo even after 50 years of metric education.
    Now having realised it was not miles and it takes ‘a few weeks’ to work out that 9000 metres is in fact 9 km then even for me that is a bit of a stretch.
    To state that 5 1/2 miles ‘is something we all understand’ is not altogether true. Why should those doing the work have to convert everything to Imperial for a mostly fully metric educated public?


  9. @BrianAC

    This sign is also the subject of a Reddit thread, where a photo is posted:

    “Metres” is spelled out making a rather verbose sign. This may have been necessary as the UK has co-opted “m” to mean miles. While it is not an official ISO symbol, the US uses “mi” for miles to avoid conflict with the SI. (However, we would have required 9 km as it is over 1000 m)


  10. @ BrianAC 2017-11-06 at 11:31
    I’m sorry you thought my response was strange. Whilst zooming past this sign I was instantly irritated by the sign being expressed in a large number of metres and having to calculate what that was in miles or yards (though I must admit that yards and metres differ by only 10%). It is on a road that I use infrequently so it did take me a few drive pasts before realising what was intended.
    Surely with all distance signs on our roads expressed in miles, both on motorways and all other roads, and tachometers displayed in miles, everyone who was brought up in this country must know what a mile is.
    I wonder why the people doing the work are using metres anyway considering that the official units of measure on our roads are miles and yards.


  11. Graham Palmer having to convert in order to get miles and yards is the way it should be. Everything should be metric only and if one doesn’t like it, the burden of conversion must be on them. Let it be a PIA. Maybe over time after doing nothing but converting, then the person will wise up and learn the metric system.

    I wonder if you are aware that the signs that say yards are really metres. So, when you see a distance of 100 yards, the sign is positioned to mean 100 m. The yards are fake. That is another good reason to just get over your hangup and learn metres.

    Just because signs are in yards or miles doesn’t mean that engineers and workers should be required to use them. They should use the best system for the job and that is SI. The people doing the work actually prefer SI as it makes their job easier. Those not involved in the work, those on the outside interloping, don’t really have a say in the matter and shouldn’t.


  12. Graham Palmer, I am not sure where you have been in the last 50 or so years, but if you care to look and read you will find many of the UK signs are metric, a couple of quick links to get you started.
    Should you have the misfortune to break down on a UK motorway you will come across the motorway locator signs, the figures given are in fact distances in km, but not marked as such as we are not meant to know that.
    As Daniel above has said, all road marker signs in 100 yard intervals are in fact 100 metre intervals as a requirement of the DfT, not the construction company.
    You can fight it all you want, but it will be an uphill push. SI is here to stay.


  13. @ Graham Palmer

    British road signs currently show heights, widths, distances and speeds in a combination of inches, feet, yards, miles and metres. Five different units and two systems of measurement! I have a photo of one particular sign that uses the letter ‘m’ to mean both mile and metre on the same sign (but the rules on this site do not allow photographs, so I cannot post it here). Why do we need so many different units? British road signs can be quite ugly, especially those on roads approaching bridges where widths are often shown in feet and inches, the distance to the bridge is shown in yards, and the height of the bridge is shown in feet and inches and metres. Not only ugly but big too. Metric-only signs are generally smaller and allow you to take in the information much more quickly, especially as many use pictograms and are international. I hope I live to see all our road signs simplified and upgraded to metric.


  14. I am still blown away by the incredibly negative impact on metrication in the UK that the government decision (or was it simply dithering?) to delay converting road signs to metric decades ago (which later got squashed by Thatcher and which therefore never happened).

    Just today I listened to a new episode of an otherwise excellent program on YouTube called “Just Have a Think” in which a non-scientist Brit presents in a most understandable way the many frightening dangers posed to the human species by the evolving climate catastrophe engendered by anthropogenic climate change.

    The entire program used metric units exclusively with one notable exception where he used “miles” where one would expect “kilometers”. Everything else was in terms of “meters”, “centimeters”, and “degrees Celsius”. (And I fully expect he would have used “liters” if needed because he has done so in previous episodes of his program without any reference to “gallons”.)

    Mind you, he used “miles” with no conversion to “kilometers” whatsoever. Why, you might ask? Simply because road signs are still in Imperial in the UK and that is what he sees and internalizes every day. How utterly depressing!

    This is just another sad example (and to me a very striking one given how much the use of “miles” stuck out like a sore thumb) of how that decision decades ago has hung on the neck of the UK like a millstone.

    Every other English-speaking country (other than the USA, o woe is me!) has converted road signs to metric. Most notably, the conversion of road signs in Canada and Ireland have resulted in the complete domination and acceptance of metric in those countries despite close proximity to a larger and more powerful neighbor (the USA and the UK, respectively) where road signs still remain in Imperial (or US Customary).

    If only we had that time machine that Doc Brown invented in “Back to the Future” so we could change history and get those road signs converted when it was so much easier to do.

    My kingdom for a flux capacitor! 🙂


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