End of imperial-only restriction signs

The Department for Transport (DfT) has announced its intention to finally end the use of imperial-only width and height restriction signs on Britain’s roads.

The long-overdue official acknowledgement that road safety can be improved by using metric measurements on vehicle restriction signs, comes as one of the proposed changes to the Traffic Signs Regulations and General Directions (TSRGD) 2002. The DfT has calculated that savings can be made from the projected reduction in costly accidents, such as bridge strikes, that currently involve a disproportionate number of foreign drivers, who generally do not understand restriction signs in feet and inches. The change will of course benefit British drivers too, as there will no longer be a need to know vehicle dimensions in two incompatible measurement systems.

In the Traffic Signs (Amendment) Regulations and General Directions 2010 consultation documents, it states:

“We are making changes to require both metric and imperial triangular warning signs to be displayed to give warnings of restricted headroom, with the upgrade being complete in four years’ time. Using the imperial sign on its own will no longer be permitted.

We are making similar changes to require both metric and imperial measurements to be displayed on all width and height restriction roundel signs, with the upgrade being complete in four years’ time. The current imperial-only signs shown in diagrams 629 and 629.2 will be withdrawn.”


“… approximately 10 – 12% of bridge strikes involved foreign lorries. This is disproportionately high in terms of the number of foreign lorries on the road network.

… Furthermore, for several years this Department has recommended, through the Traffic Signs Manual, the use of the dual unit height limit warning and regulatory signing in preference to the imperial only alternative.”

This is a welcome development. However, by replacing imperial signs with dual unit signs, an opportunity is being missed to make further savings, as in the not-too-distant future, the new dual unit signs themselves will be replaced with Vienna Convention-compliant metric-only signs. Garage forecourts, warehouses, and many car parks have already been using metric-only height restrictions for many years.

The proposed amendments to the TSRGD have come about as part of the Traffic Signs Policy Review, which was announced in September 2008. UKMA’s contribution to the review included the production of a leaflet, Traffic Signs 2.0, which highlights the many issues within the remit of the review that can be solved by switching to metric road signs. Unfortunately, the DfT continues to refuse to consider switching to metric measurements on road signs, and as a consequence it has dismissed the proposals in the leaflet, apparently even the recommendations that are not directly related to metrication, such as the use of language-independent up-arrows to indicate hazard extent, and the replacement, where possible, of text-only signs with standard pictograms.

As an example, the DfT has overlooked the principles of the 1968 Vienna Convention on Road Signs and Signals in the proposed new warning sign (diagram 7014.1) that indicates a temporary or permanent reduction to bridge headroom. The sign is text only, and consequently a non-English speaker might be unaware that the figures in brackets relate to a height restriction.


The diagram below illustrates how the essential information in the sign can be shown in a language-independent way using standard symbols from the Vienna Convention.


The Vienna Convention does not prescribe feet and inches on restriction signs though, and stipulates that the measurement units should be in metres only.

Traffic Signs Policy Review

Details of the Traffic Signs Policy Review can be found at the following link.

You can apply to join the Traffic Signs Policy Review sounding board, or comment directly using the following e-mail address traffic.signs@dft.gsi.gov.uk

You can comment on the new signs and other proposed amendments to traffic signs regulations in the DfT consultation, details of which can be found at the following link.

UKMA’s Traffic Signs 2.0 leaflet can be downloaded by clicking on this link.  Alternatively, free printed copies can be obtained by e-mailing secretary@metric.org.uk

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23 Responses to End of imperial-only restriction signs

  1. Robin Paice says:

    While this is welcome as far as it goes, I have two comments:

    1. The target is apparently 4 years from when the new amendment comes into force (probably some time next year). Why do we have to wait so long? According to the DfT's own rather dodgy figures, the changeover will result in savings, and it is obviously a safety issue. So why can't it be done in, say, 12 months?

    2. Although they are currently in denial, eventually the DfT will have to concede that the changeover to full metrication is inevitable (just as they have finally admitted that imperial-only signs are no longer sustainable). Why therefore do they not permit metric-only restriction signs (in the red circle) alongside an imperial-only sign - like the two side-by-side triangular warning signs? This would enable the imperial-only signs to be removed when road signs are converted generally, leaving the metric-only sign in place, thereby reducing clutter and improving clarity. The DfT appear to be acting as they though believe that metric conversion will NEVER happen. However, this is contrary to the Government’s stated policy of gradual conversion (ref. Tony Blair in a letter to Lord Howe in September 2004). By maintaining this head-in-the-sand approach the DfT is actually increasing the eventual cost of conversion.

  2. Mark Preston says:

    Three quick points that I'd like to make here ;

    1. No mention seems to have been made of length restriction signs

    2. The DfT has said itself in the past that it thinks dual signage for distance and speed signs would be dangerous yet is to allow them for height and width restriction signs.

    3. I agree that what should happen is that over the next 2 years or so a single metric restriction sign should be put in place alongside an imperial one (not a dual sign). The DfT should require, over that period of time, that vehicle manufacturers, haulage companies, bus companies, drivers etc install in cabs metric only height and width information. As I understand it they must currently show imperial measure, sometime with metric alongside. This could be checked as vehicles are inspected each year. At the end of the two years, all imperial signage shoul dbe taken down leaving only metric height, width and length restriction signage.

  3. Martin Vlietstra says:

    This is a welcome move.

    On a practical note, I think that there is room for one minor improvement to the proposal - namely that the two signs, one metric and one imperial should actually touch each other, espacially where two or more bridges are concerned. I actually know of one road sign in Haslemere which details THREE bridges - each one different.

  4. Jeremiah says:

    This is good news in that it is a foot in the door. Hopefully though the use of dual units will cause equal confusion to the point that the imperial will have to be removed sooner.

    With dual unit width and height restriction signs I can see the use of dual distance and speed signs not far behind. How many foreign lorries have miles and miles per hour on their gauges? Zero I would suspect. So how are they able to comply with speed regulations?

    Not knowing what a mile, yard or foot means, how many cause traffic mayhem when they incorrectly judge a distance and then try to correct for it? Consider a driver needing to turn at a specific intersection and is surprised when it appears sooner or later then expected and the driver causes an accident trying to change lanes quickly or has to make a U-turn to get back to the right road causing an accident in the attempt.

    Even though dual signage is not ideal it is better then no metric signage at all. The metric haters don't even want this for fear that exposure to metric on the signs will soften the resistance of the population to the point where they will become pro-metric or indifferent to increasing metrication. Road sign conversion is really the last major obsticle to complete metrication in the UK.

    I am wondering though if the metric distances will be converted imperial, or based on measurements. Converted imperial can give metric numbers that are impractical, especially if the person(s) making the decisions on what the metric numbers should be wants the metric to look ridiculous. Maybe the 4 years time is needed to remeasure all bridges so as to get accurate numbers instead of assuming the present ones are correct.

    This might be the opportune time for the UKMA to push for metric speed and distance signs and thus for all new cars sold int he UK to be metric only. Just like Ireland.

  5. David King says:

    This is long overdue, although probably not far enough nor quick enough in getting rid of all imperial-only signs from our roads. We need metric signs. I started seeing the metric height restriction signs back in the early 1980s (or possibly it was late 1970s), and expected the changeover of all these signs to metric to be completed within a few years, rather than a few decades.
    Hopefully we can have metric-only signs as well where councils so choose to erect them (if they are forward-looking enough).

  6. Ezra Steinberg says:

    The headroom restriction sign is a disaster on all fronts.

    * It is an established fact that text in all capital letters is harder (and therefore slower) to read that mixed case letters because capitals all have roughly the same shape (i.e. a rectangle) whereas readers have stored clues about the shapes of words in mixed or all lower case.

    * The situation is even worse for drivers who read English poorly not at all. It will be difficult for them to reliably make out the text of the sign while traveling at any speed or if the sign is partly lost amid surrounding clutter. It is well established that well designed visual signs are much more quickly processed by the visual cortex than text signs, which must be processed through a much more complicated neuro-cognitive path in the brain.

    * Who on earth thought of white text on red background when 11% of males suffer from red-green colour blindness? Those individuals will find this sign even more difficult to make out. Make them a foreigner and you can see what the liklihood is they'll sort out the meaning in time, especially with the metric value (the one they can understand) buried at the end and cluttered up with parentheses).

    * As others have said, the sensible approach (short of metric only signs) is to have 2 separate signs (one in Imperial and one metric) using the established international designs so that the Imperial signs can be easily removed as part of an "M" day conversion to metric only road signs.

    One can only hope enough pressure can be brought to bear to bring DfT around and show some good sense for a change.

  7. Tim Bentley says:

    Whilst wanting to see the complete metrication of all road signs done as soon as possible, I accept that with a General Election looming this is unlikely and is something which an incoming government should get to grips with early in a parliament.

    However,I think some progress is possible during this reveiw,in particular the replacement of the yard with the metre. This can be achieved without replacing or relocating any signs as they are already set out using metres! The signs can be changed using high quality vinyl overlays which should, if applied carefully, last the lifetime of the sign without fading or peeling.

    The only slight confusion which can easily be addressed are the very few signs which at present use the m for mile. I suggest as a temporary measure, until km signs are introduced, the abbreviation mi can be adopted.

  8. Richard Birkby says:

    Jeremiah asks "How many foreign lorries have miles and miles per hour on their gauges?". I can't speak for lorries, but having taken my annual summer holiday in Britain in my non-British registered car I can answer his follow-up question of "So how are they able to comply with speed regulations?"

    The answer is - badly. Keeping to the urban limit is relatively simple, as it is 50 km/h as a general limit all over Europe, and one already has the mentality of keeping to that speed in built-up areas. However, the conversion to other limits is far from automatic. It requires maths and thinking.

    I remember once reading an article in one of the more anti-metrication newspapers about how high the number of non-British-registered cars detected speeding by cameras was near ports, along with comments such as "why do we let foreigners get away this" etc. (I'm afraid that despite googling I have not been able to come up with this online - perhaps someone could help?) Frankly, I am not surprised so many newly-arrived drivers are confused. It is bad enough having to adjust with a different country's different rules of the road without having to get your head round what is by no means an easy mathematical formula.

  9. Peter K says:

    I can't believe that a panel of traffic signs experts spent 12 months coming up with that new bridge headroom sign.

    It could quite easily be seen as one of the those strange new journey-time signs.

    12 minutes 9 seconds (3.8 miles).

  10. John Frewen-Lord says:

    In response to Richard Birkby's comment, while I wholeheartedly agree, we must be a little careful in assuming that 'foreign' drivers cannot cope with mph. Some of us are old enough to remember driving 'on the Continent' (as we called Europe then) in cars that had no km/h markings at all. Somehow we coped (and were advised that using the excuse that you forgot that the '60' sign meant km/h and not mph just didn't wash when the gendarmes pulled you over - and no, I never got a speeding ticket in Europe).

    Likewise when I lived in Canada in 1978 when it converted on Labour Day that year, few cars had supplementary km/h markings at the time (unless bought new that year, when most were dual marked, km/h predominant, or else km/h only, even before the signs had been converted), yet we still managed to get used to the new speed limits very quickly.

    I am not in any way condoning the use of imperial signs - far from it, I want them GONE! - just that we must be careful to use arguments that will stand scrutiny, or else the anti-metric crowd will use them against us.

  11. Richard Birkby says:

    In case I left any readers doubting whether I was condoning breaking speed limits by my earlier comment, I can assure any readers I was not, and I am grateful to John Frewen-Lord for his clarification and remarks on the changeover in Canada. Nevertheless, I do maintain (from experience) that the hardest part is getting used to limits on entering the country (i.e. at ports), especially when coupled with getting used to (or re-acquainting myself with in my case) the different rules of the road, which are markedly different from any of Britain's neighbours other than Ireland. It is, in other words, a risk that could be diminished by metrication.

  12. Derek says:

    Several reasons could be found to explain this proposal:

    * ‘Papering over the cracks’. Another attempt by the DfT to sustain the unsustainable – imperial measures on UK road signs.

    * Part of a carefully considered long-term plan by the Department for Transport (DfT) to convert road signage in an efficient, cost-effective and safe manner. Highly unlikely, in view of the DfT’s (and its predecessor the Department of Transport's) long term hostility to the idea of the changeover, spanning 44 years, thirteen governments, and goodness-knows-how-many Ministers of Transport.

    * “An EU ploy” aka “metrication by stealth” aka “the thin end of the wedge”, all suggestions put forward by MEP Derek Clark in Monday’s Today programme on BBC4. If there is a conspiracy, then MEP Clark should be in a good position to obtain evidence. So far none has been forthcoming.

    If we accept ‘papering over the cracks’ as the most likely explanation, then where are the paper hangers at the DfT likely to head for next, now that the concerns relating to cost and safety which have been raised by bridge owners and lorry fleet operators have been addressed?

    To Northern Ireland? An increasing proportion of cars crossing the border from the Republic to NI have km/h only speedos, while in the UK several manufacturers, including Mercedes, have introduced mph-only speedos in new models. And there is that famous coastal road which over a short distance crosses the NI/RoI border many times, with consequent changes in speed limit.

    To Wales? A recent posting on MetricViews illustrates the cluttered signs that result from imperial’s use of abbreviations, doubled if two languages are used, and also shows the simplicity that results from metric’s use of symbols.

    Into the motor trade? The UK is now the only significant market for right-hand drive mph cars. This is a bane for manufacturers, and results in increased costs to motorists, whether buying a new car or attempting to ship a car into or out of the UK.

    But if the DfT paper hangers are at a loose end, here is a suggestion for them. How about looking at the inflated estimate of the cost of the changeover produced in 2005? In these financially straightened times, should the changeover really cost per head of population about ten times that of similar schemes in Ireland in 2005 and in Commonwealth countries in the 1980’s and 1990’s?

  13. Mark preston says:

    I have thought that perhaps, unintentionally maybe, that this might be the first step to full metrication. If we now accept that weight restriction signs are wholly metric, we now have height and width (and possibly length ?) restrictions in dual units.

    I can see a situation arising in maybe 5 years or so where a decision is made, on the grounds of cost or safety to remove or not replace the old non SI signs. The DfT has stated that dual measure signs for speed and distance are not desirable so how much longer can we have dual height and width restriction signs ? In which case, in 5 - 10 years time feet and inches will disappear from our road signs for good ?

    Then an argument can be made for a better understanding of metric measurements, especially the metre. As the yeard and the metre are very similar measures i can see short distances being converted from yards to metres, especially something like the speed humps signs. I live near a junction which has a sign pointing left which states humps for 3/4 mile and a sign pointing right saying 475 yards - anyone know how these two measures relate to each other ??

    Then in time we move towards km for longer distances and then finally speed limits in km/h.

    I reckon we will eventually see metric road signage by about 2025. It depends perhaps on whether the US 'bites the bullet' and decides that it has had enough of imperial measures and makes the switches any time soon.

  14. Derek says:

    UKMA has received contributions to this debate from two of its contacts abroad.

    Pat Naughtin writes from Australia:

    “It is interesting to note that changing all road signs in an entire nation can be done in a day – that's right – in a single day.

    It all depends on the method you choose. Australia, New Zealand, India, South Africa, and Ireland chose successful methods largely by copying each other’s successes. They all chose to change to metric only signs and the job done in a day was the result.

    Others have chosen other methods based on simple conjectures or prejudices. The UK chose two methods that have proved to be unsuccessful so far:

    1. Design, build, and repair roads all in metric measures while you provide the public with signs based on the metric inch, the metric foot, the metric yard, and the metric mile that were all defined in metric terms in 1959. This truth was hidden from the UK people by an arbitrary decision made at the time of the Thatcher government – it was based on a simple political prejudice that was encapsulated in the phrase 'WE have saved the pint and the mile for Britain'.

    2 'Dual signs are good for educating the public' is an interesting conjecture that, as far as I can find, has no basis in fact and no precedent in history. It is simply a false conjecture that has always proved to be false wherever its application has been attempted.

    These two thought have led to the current situation in the UK. They began to use this prejudice and this conjecture in about 1965 and there are many who still support them even despite their obvious failure after 44 years – so far – and with many more years still to come!

    Remember that the alternative is to look at a nation that has made the upgrade in a single day and copy the successful methods that they chose to use.”

    You can contact Pat at pat.naughtin@metricationmatters.com, or to get the free 'Metrication Matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.

    John Frewen-Lord writes from Canada, adding to his earlier comment on this topic:

    “Canada converted all its speed limit signs in one night. Went to bed, signs were in mph. Woke up next morning, all were in km/h. The stick on solution was used - very cheap, very fast, and very effective. Most lasted until they needed to be replaced for other reasons.

    When you consider Canada's vastness, and the fact that every road has speed limit signs by the million (roads 60 km/h and under by law have to have signs every 500 m [exception - blanket '50 km/h unless signed otherwise' signs when entering a metropolis], while those roads over 60 km/h had to be signed every 1 km, including freeways), this was quite some achievement.”

  15. Derek says:

    Pat Naughtin has added the following to his earlier comment:

    "Our road sign metric transition was similar to the one in Canada except that a Sunday was chosen so we could do things in daylight. For several months beforehand, new signs were put up and covered with a sort of hessian sacking material. All that had to happen on the Sunday (1974 June 1) was to remove the sacking and take away the old signs.

    The whiners (called whingers here) had a lovely time with conjectures describing bloodshed on all of our roads – but like their other conjectures these had no basis in fact, in history, or in reality. To quote from the report, Metrication in Australia:
    Despite suggestions by people opposed to metrication that ignorance of the meaning of metric speeds would lead to slaughter on the roads, such slaughter did not occur."

  16. Richard Birkby says:

    Derek (2009-10-22) made the point about the UK being the only significant market for right-hand drive cars using imperial measurements. As a matter of fact, I think I am right in saying it is the only country with such a market, as the very many other countries that drive on the left are all metric. This however I think is not relevant as far as it is implied that it is what the motor trade wants, as (i) national markets almost always differ to a slighter or lesser extent anyway and (ii) I would respectfully suggest that this is not the forum to discuss such an issue. (For what it is worth I most definitely think such a switch in Britain would be a lot of pain for very little gain.) Nonetheless, I do think, as I stated in my earlier posts, that metrication - which would be very little (if any) pain for a lot of gain - would undoubtedly ease matters for drivers arriving at a British port as they would not have to worry about converting all the time to imperial while also concentrating on adjusting to the different rules of the road.

  17. Derek says:

    “METRIC signs are to be placed on Britain’s roads at a cost of at least £3million to end the chaos caused by foreign drivers” headlined the Daily Express on 20 October. Or, looked at another way, “METRIC signs are to be placed on Britain’s roads … because the UK failed to carry out the conversion when first proposed in 1973”.

    Putting this figure of £3 million in the context of Government expenditure, I noted this in today’s London Evening Standard:

    “£2 million cost of delay of house sale
    The Government’s delay in selling the Belgravia house last occupied by David Blunkett could cost taxpayers £2 million. Mr Blunkett was forced to resign in 2005 but stayed in the house until 2007.”

    And, as Robin pointed out in the “Today” programme, the metric signs will cover their costs by reducing damage to bridges and delays to rail passengers and other road users.

  18. Michael Glass says:

    As there is some movement on road signs, this might be the time to push for revising the law that anti-metric campaigners have used to stop people using metric signs. That change would discourage zealots from defacing signs on the pretext that they do not comply with the law.

  19. Mike Joy says:

    After wondering for many years why the UK is so tardy in switching to a system that is favoured by so many, many countries, I did my own investigations.
    When I heard that the results of a survey in England were to retain MPH on road signs, especially by younger people, I decided to dig deeper.
    My opinion is that the culprit is our friend Jeremy Clarkson and his popular TV program 'Top Gear', where he stresses Imperial units and totally disregards metric measures as if they don't exist - even on trips outside the UK.
    So it's easy to put two and two together and you can see Jeremy's formula of Fun = Imperial Units, and any young person will soon forget what he's taught in school about the metric system being the preferred system.
    The US do the same with their 'Mythbusters' program, where complicated calculations are made to look easy using their non-decimal system, and no mention at all of SI units.
    So until someone produces a fun show that promotes the metric system, we will always have the brakes put hard on when it comes to metrication in the UK or the US. Fortunately, we did not have these trouble-makers around when we moved to full metrication 40 years ago.
    Mike Joy
    Perth, WA

  20. philh says:

    I am inclined to the view that our failure to convert road signs are a major factor in the UK population not fully embracing metric.

    The opinion of young people varies but they are generally conscious of the disparity between what they are taught in school and what they encounter outside the classroom. They have grown up with imperial road signs and have adapted to them. They may not have any appetite for the change if they don't value their education especially in mathematics and science.

    This gives the lie to the broad assumption by the DfT that the mental preparedness will take care of itself as new generations of drivers populate our roads.

  21. John Steele says:

    Was the law changed to also require metric on height and width clearance signs? Does it only apply to new signage or is there a date by which existing signage be rectified and brought into compliance.

    I am curious because of this story about problems with over-height vehicles in Surrey:

    Local resident's suggestion is the article title and says it all, "Make sign EU-friendly to stop stuck lorries."

    I am surprised by the town's cavalier attitude and wonder if the law never changed, they don't know or care about the new requirement, or if they are allowed to delay complying for a while. The town has a problem and could easily fix it but instead prefers the position snipped from the article:
    Jean Parry, who has lived near the bridge for 10 years, believes the problem is getting progressively worse.

    She said: "It is on a daily basis, twice daily sometimes, and the police are called frequently. Surrey highways said the signs comply with legislation but the big problem is that a lot of the drivers are foreign and they don't know what it means in imperial measurements.

    "I said 'can't you put up a sign saying three metres?' and Surrey said their signs are already compliant with legislation."

  22. Martin Vlietstra says:

    I don't know if the town's MP can help, but it is rumoured that the MP in the neighbouring constituency might be able to do something about this problem - after all he is Philip Hammond, Minister for Transport who was responsible for blocking the mandatory use of metric units on hieght restriction signs.

  23. Ezra Steinberg says:

    Is there a way for UKMA to make use of this sad situation to "shame" Mr. Hammond and the coalition government to re-adopt the Labour government's position to add metric signage for height, width, and length restrictions? After all, isn't the government all about not wasting taxpayers' money these days?

    I'm also wondering if there are any Lib-Dem members of the government who are more open-minded about this sort of thing and can be appealed to.


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