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.

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11 Responses to Metrication timeline for British road signs

  1. Ezra Steinberg says:

    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. Daniel Jackson says:

  3. Cliff says:

    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.

  4. Lee Kelly says:

    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.

  5. Daniel Jackson says:

    @ 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.

  6. Michael Glass says:

    The least they could do is to get the heights and widths right in both measures. See for what can happen when the metric measures are not right.

  7. Alex Bailey says:

    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.

  8. Ezra Steinberg says:

    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.

  9. Graham Palmer says:

    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.

  10. BrianAC says:

    @ 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?

  11. John Steele says:


    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)


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