Road safety experts ignore UK sign problems

A recent report into the safety implications of variations in road signs across Europe has ignored problems caused by the UK’s continued use of imperial units.

In the last decade, 2 million Europeans lost their lives or suffered crippling injury on our roads. In purely financial terms, this costs a staggering 2% of European GDP.

In June 2011, two international road safety organisations jointly issued a consultation document, “Roads That Cars Can Read”, in which they forecast that thousands of European lives will be saved once the use of technologies such as in-car road sign recognition systems become as universal as today’s satnavs. The two organisations, the European Road Assessment Programme (EuroRAP), and EuroNCAP, are both dedicated to reducing the number of serious road accidents throughout Europe, and believe that these figures can be drastically reduced by improved road design, and the use of standardised road signs.

The report points out that, after over half a century of international treaties intended to standardise road signs worldwide, there remains “marked variation between countries even on the most common signs”. In addition to the safety implications of poor uniformity of road signs, these differences hinder the ability of future in-car road sign recognition systems to correctly identify signs. The report states that, “It is sure to be true that roads that can more easily be read by machines will be safer for road users generally too”.

As examples of how signs vary, the report shows 3 key signs as implemented in 5 different countries.

However, more obvious and serious differences between UK signs and those of all other European countries have been ignored. The signs below show speed limits as seen in the UK, France and Germany.

Whilst here too there is a lack of uniformity in the use of type faces and the thickness of the outer red circle, there is a far more important difference between these signs. Although superficially similar, the UK sign is alone in not having the same meaning. It prescribes a completely different speed limit from the other signs.

The report also erroneously asserts that “all countries appear to follow the principles of the UNECE protocol agreed in 1949 and revised in 1968”, whereas in fact UK vehicle width, height and length restriction signs are non-compliant because they do not use the units of measurement specified in the protocol, which are metres only.

Section C, II, 1(e) of Annex 1 of the Vienna Convention on Road Signs and Signals specifies the units for vehicle restriction signs:


The publication of “Roads That Cars Can Read” comes only weeks after a decision by Philip Hammond, the Secretary of State for Transport, to ignore the outcome of an earlier Department for Transport consultation which had recommended that all width and height restriction signs be shown in metres in addition to feet and inches.


The Vienna Convention on Road Signs and Signals 1968 is an international treaty designed to increase road safety and aid international road traffic by standardising the signing system in use internationally. Its signatories include the UK and more than 50 other countries worldwide.

56 thoughts on “Road safety experts ignore UK sign problems”

  1. I’m wondering if there is any kind of consultation that the UKMA can provide after the fact (since the report has now been published) to perhaps persuade the two authoring groups to issue an addendum that addresses the issue of Imperial units on UK road signs.


  2. What I find interesting is that the report focuses on comparatively trivial differences between different countries’ signs (the thickness of the red ring) yet it ignores the fact that almost identical signs may have a completely different meaning in different countries (because they use different measurement units). A British driver who interprets “50” in France to be “50 miles per hour” could cause a serious accident. The DfT’s persistence in clinging to imperial measurements is actually a risk to road users in other countries.


  3. The British position on road signs is extraordinary, especially on vehicle dimension signs, which as you point out do not comply with the Vienna Convention. It would be interesting to see a highway authority or the UK government taken to court over an accident caused by failure to implement the adopted treaty properly.


  4. I’m not defending UK signage; I agree it should change to metric.

    However, I’m not so sure the signage violates the Vienna Convention. I skimmed it, and it seems to be a rather inclusive document, with alternate examples of several signs. It explicitly allows speed limits in both kilometers per hour and miles per hour, using the most prevalent units in each country, either as a standalone number or with units underneath.

    For width and height restrictions, the example sign and text refer to metres, but the unit symbol is on the sign. It is very hard to say whether they are insisting on metric or just giving an example. If the units are shown on the height/width restriction, is it really non-compliant? I have trouble accepting that they mean to be so exclusive on this when they are so inclusive on speed.


  5. The article does not claim that UK speed limit signs are non-compliant with the Vienna Convention. The Convention clearly permits the use of either mph or km/h. The article however does make a case for there being a safety issue with one country using different units for speed limits from all its neighbours.

    Width and height restriction signs, on the other hand, are clearly required to be shown in metres only. Nowhere in the Convention does it stipulate that feet and inches are a permitted variant or can be used to supplement metric units.

    On the contrary, Chapter I Article 3 section 1(a) states:

    (i) Where this Convention prescribes a sign, symbol or marking for
    signifying a certain rule or conveying certain information to road-users,
    the Contracting Parties undertake, subject to the time-limits specified in
    paragraphs 2 and 3 of this Article, not to use any other sign, symbol or
    marking for signifying that rule or conveying that information


  6. To repeat part of an earlier comment:
    ‘Is it the Government’s aim to make Britain’s roads the safest in the world?’
    [Just another DfT consultation]


  7. I posted a similar observation in a thread on the SABRE UK forums about metric signage:

    It seems pointless to have pictorial signs that are 90% the same as every other country in Europe and then use different units on them. A height warning sign is recognisable to anyone from Europe but the actual information it contains is meaningless. Since there are so many costly bridge strikes involving foreign HGVs on our roads, and if the Vienna Convention does indeed require metres anyway, there can be little argument left that our dimension signs should be converted to metres without further delay.

    I imagine one of the DfT’s logistical obstacles with changing height warning signs in particular is the Road Vehicles (Construction and Use) Regulations 1986:

    Regulation 10, Paragraph 2 states:

    “No person shall use or cause or permit to be used on a road a vehicle to which this regulation applies if the overall travelling height exceeds 3.66 m unless there is carried in the vehicle in the manner specified in paragraph (3) a notice clearly indicating in feet and inches and in figures not less than 40 mm tall, the overall travelling height.”

    How bananas is that? If your vehicle is more than X metres high, you must display its height in Y feet/inches!

    Compounding this problem is the fact that most HGVs are fitted with plastic reconfigurable indicators showing heights in ft/in only, e.g.:

    We’ll only see an end to imperial dimension signage once this particular regulation is brought up-to-date and the transport industry has been convinced to change all their height indicators.

    It’s hardly a major obstacle, if we’re honest. All it needs is to be done.


  8. Isaac has pointed out that the article makes a case for for there being a safety issue with one country using different units for speed limits from all its neighbours.

    The current situation with respect to the Irish Republic and Northern Ireland makes this issue even more acute now that there is a land border between a country that uses metric-only signs (including speed limit signs) and a portion of a country that uses Imperial-only road signs.

    And it is really correct that the Vienna Convention prescribes metric-only signs for height, width, and length restrictions? If so, is there legal action that UKMA (for example) could undertake?


  9. Vienna Convention workshops:
    In 2009 I asked my MP to find out why the DfT wasn’t participating in the
    Vienna Convention workshops. Below is part of the reply from the duty minister:

    ‘We no longer participate in the UNECE working party on
    road safety because from past experience this forum has added little
    value and does not justify the resource that would be involved, in
    terms of officials’ time and the expense of attending the Geneva
    meetings. However, we do participate in European Union road safety activities,
    in particular the EU High Level Group on Road Safety, as well as
    regular bilateral contacts with those countries with which we have
    most in common on road safety and from whose experience we have the
    most to learn, such as the Netherlands, Sweden and Norway. ‘

    Chris Mole MP
    Duty Minister ‘


  10. Among the many excuses successive British Governments have used for not making the change to metric on roads is the one purporting the risk to road users during the change.

    Yet this article and many of the comments above point out that the risk to road users in switching between different units when crossing our borders is cheerfully ignored by those same government ministers.

    I can only conclude that the latter risk tends to be disregarded because it mainly affects foreign drivers and does not led itself to popular support. This in spite of the fact that a foreign driver on British roads who has difficulty in assimilating imperial units present a risk to all other road users as well as themselves.


  11. The safety issues that arise from the use of different units on similar signs are an obvious safety risk. I believe that it would be good if the UKMA sent a letter or email based on Hughster’s posting on the Sabre website to every Northern Ireland MP and every Northern Ireland newspaper.


    At the same time, the UKMA should approach the UK ministers for transport and ask them if they would stand in the way of Northern Ireland metricating their road signs if this should be the will of the Northern Ireland Parliament. Whether or not they agree, their answer should be communicated to the Northern Ireland legislators.

    If the ministers say no, they will be open to the charge that they are not prepared to listen to the will of the Northern Ireland legislature; if they say yes, then the Northern Ireland legislature will no longer be in the position where it can duck-shove this decision onto Whitehall. Remember, support for metrication of road signs is not yet overwhelming in the NI Parliament, but it is much stronger than it is in England, so I think it’s worth a go.


  12. To add to everyone else’s comments, I wonder if there have been any verified incidents of people driving at 30km/h in a 30mph section, 40km/h in a 40mph section, etc. in the UK? Or going at 10km/h when the minimum speed limit is 10mph…

    Plus, I would have thought that motorists could get extremely annoyed (if not severely cheesed off) if they are following someone driving at 40km/h in a 40mph (64 km/h) section of a single carriageway, or 20km/h in a 20mph (32 km/h) zone, assuming there is no traffic jam.

    This is in addition to (as mentioned by everyone here) the risk of bridge strikes due to imperial-only signs not being understood, and the risk of British drivers causing a serious accident due to forgetting that speeds are in km/h not mph (even if in practice, the vast majority of British drivers do cope when abroad), these are surely serious safety concerns.


  13. The highway code says that motorists should keep up with the flow of traffic.

    I happen to know of a case where a learner driver failed his test for going too slowly. This was on a quiet out-of-town road where the limit is 60 mi/h and he was doing about 40. I am told that during the test, the learner is expected to travel at or slightly below the speed limit if conditions allow.

    This may be partly to do with demonstrating confidence but it is also a safety issue. On my route to work I often see cars struggling to get past slow vehicles or obstructive motorists and, as a result, taking chances.


  14. There is a program on Dutch TV, named Wegmisbruikers (Road Abusers). And indeed, some British motorists who were pulled over had misinterpreted Dutch speeds signs, like ’50’, ‘100’ and were fined. Dutch speeding fines run into the hundreds of Euros and an offender who drives more than 50 km/h too fast, will see his/her drivers’ licence confiscated on top of the fine and the DPP decides what happens to it. Either the offender gets it back within a few weeks, or there will be a decision during a court case; the offender’s past record is taken into consideration. A British motorist who misinterprets a sign ‘100’ on a Dutch motorway exceeds the 50 km/h rule as he drives at 160 km/h. Non-Dutch nationals however are offered to pay a fine in such cases but that is 400 euros!


  15. The Surrey Advertiser has publisher reports of yet another continental lorry causing a traffic jam due to the driver not understanding an imperial-only height restriction signs. Local resisdents are calling for metric units. (See

    The MP for the neighbouring constituency is Philip Hammond, the Minister for Transport who blocked the legislation making dual signing of height restriction mandatory. Lets see if the local MP is going to talk to his neighbour – they are both members of the same party.


  16. But the Surrey council is not blameless in this either. Dual height height restriction does NOT need ot be made mandatory for them to fix the problem. It merely needs to be allowed and it is under the existing 2002 Traffic Signs acts. They simply don’t care about the problem or the resident’s concerns.

    If the article is true and it is a “daily” concern, the cost of living with the problems seems like it would be higher than the cost of the sign to fix the problem.

    At the local level, that lack of concern for residents’ issues is a good way to got unelected.

    None of that deflects blame from Mr Hammond. The way to fix it across the UK, and in advance of an issue at every bridge is to make it mandatory. However, councils that care can correct documented and continuing problems on their own (if only they cared).


  17. Ironically, the local council not caring opens the door for a national discussion that the DfT can hopefully be made to respond to.

    If Surrey had quickly put up their own signs and made the problem go away, the issue would have evaporated. So, the silver lining (one hopes) is that pressure can be placed on DfT by appropriate business groups (because those are the folks with the most leverage with the Tories, I presume) to insist on change.


  18. The problem is getting the authorities, local and national, to recognize the connection between non-metric warning signs and some cases of bridge strikes.
    Common sense would suggest that imperial only signs are bound to be a risk factor for drivers who do not know the height and width of their vehicle in feet and inches, but unless there are documented cases where the cause of the accident was reported to be failure to understand measurement information on warning signs, it won’t be taken on board. With the likes of Mr Hammond the common-sense point of view tends to be overshadowed by prejudice.


  19. @Phil

    But rather than administering an Imperial quiz to the driver, perhaps the license of the driver and/or registration of the truck could be used as a surrogate. If not UK, then assume a misunderstanding of Imperial may have contributed. There will be exceptions in both directions, but it may provide a good estimate from existing police reports.

    In the case of naturalized UK citizens, you may have to ask where is he originally from and how well does he understand imperial. I wouldn’t count on all UK citizens understanding it well either, although it should be an element of a commercial license exam.


  20. One of the biggest problem with local authorities seems to be that they’re only concerned with their current budget and the bottom line at the end of the current financial year. Last time I spoke to my local authority to query their policy on dual unit signs I was very much told that they did nothing more than was legally permissible at the lowest possible cost.

    What this seems to come down to yet again is that unless a higher authority insists on metric on these signs then it’s going to be a long time before it happens.


  21. Perhaps this is a time for local action. Why not design and produce appropriate warning signs, tip off the media and then erect the signs. The more publicity the better.

    If the local authorities stop you or take down the signs, they are to blame for putting petty rules and penny-pinching attitudes ahead of public safety. If anti-metrication groups try to weigh in, they can be accused of putting little England prejudice and pig-headed stupidity against the public interest.

    You have a wonderful opportunity to generate publicity. Seize the opportunity!


  22. The following was picked up from a road enthusiasts website (

    I wonder how many drivers have any idea of how wide their vehicles are when comparing them to a width restriction notice.

    My manual gives it in both Metric (2000 mm) and Imperial (78.8″) over wing mirrors. So even with that, nothing to compare easily with a sign in feet/inches.

    Bodywork is 1790 mm, 70.4″. I seems that when driving on the M4 from Heathrow into London I am not permitted to use the perfectly normal-sized lane 3 (the old bus lane) because this has a signed limit now of 6’6″, unless I pull in my wing mirror a bit. Likewise any lane 3 through motorway roadworks, signed as 6’6″. Until I wrote this I never realised.


  23. I like Michael’s idea of taking some action on the very bridge posing a problem to generate publicity.

    But after this whole riot thing (and the Eurozone stuff) has settled down. (Guess that could be a while?)


  24. @ Martin,
    When it is a legal restriction rather than a physical limitation, what width prevails?

    The US limit basically only applies to commercial vehicles as it is 102″ (Now it is officially 2.6 m, which is 102.36″. NAFTA??). However, mirrors and side marker lamps are specifically excluded so as not to encourage unsafe running configurations. The limit is widest part of the body, excluding those items.

    NOTE: That limit is Interstates and State highways. States may designate 96″ max on local/county roads.


  25. Very pleased to see that at Lechlade in Wilts, the warning sign for the narrow bridge warns approaching vehicles that they must be 13m or less. No imperial indication at all. Unfortunately, a few metres down the road, their is a width restriction in feet and inches and a warning sign for a lay-by in yards.


  26. Someone ought to take some pictures of what michdung has just described at Lechlade and post it on the UKMA website … and then pass it along to as many media outlets and organizations interested in road safety, etc. that you guys can think of to solicit their comments.

    Sadly, the situation at Lechlade sounds like the quintessential example of the metric muddle in the UK, which is why I suggest highlighting it somehow in the public’s mind.


  27. Some Daily Telegraph journalists use “kph” as an abbreviation for kilometres per hour. Sadly these are their science correspondents. Only a Liberal Arts Muppet would use “kph” rather than km/h (km/hr). “Where’s the metre, Muppet?”
    Justification given is that “kilometre” is one word, thus the abbreviation would be “k”.
    But then “kilogramme” and “kilowatt” are also one word. Can you provide a more brutal rebuttal?


  28. @Jack

    Perhaps tell them it is only an abbreviation for kilometers per hour as Americans at Associated Press invented it. USMA has been trying to correct AP for at least a decade (to little avail). See this message as USMA archive list server:

    It has a link to a Word document which I sent to the three AP Stylebook editors and addresses several metric errors the AP makes. The letter is fairly specific to the AP and American journalism, but perhaps the points can be modified to be suitable for use with the British press, and I invite anyone to so use it.

    Perhaps the strongest argument for automotive writers is that, under US law, kph is illegal on a speedometer, a secondary kilometers per hour marking must be marked km/h. I have no idea what the case would be under British law.


  29. Personally I am just glad that the Daily Telegraph is using metric measurements 🙂


  30. Thanks, both. Problem is that The Daily Telegraph uses metric and imperial measurement in the same article, paragraph, sentence. Even “miles per litre” is a distinct possibility. So it’s the DT’s lack of professionalism and “mishmash” of terms that is the main problem. Obviously compounded by “Trash Culture UK” which ridicules learning and education as elitist. So I can see why you have you have your work cut out in convincing the British general public that metrication is the way forward.
    Jack, Japan Alps


  31. @michduneg

    I certainly understand that point of view. When it is an isolated error, and they are open to correction, I agree with it. They should be thanked for using metric and gently corrected.

    When it is an institutionalized error and they refuse to correct it (as is true of AP and the American press), I have to wonder about it. I wonder whether they are arrogant, obstinate, stupid, innumerate, or have an ulterior motive. The only ulterior motive that makes sense is further confusing the public and forestalling metrication. In two contexts, that confusion creates some safety risks.

    Roads: Automotive writers insist on using kph to refer to kilometers per hour. Yet the Federal government requires a secondary speedometer indication, if used, to be labelled km/h. Unlike the UK, metric speed limits are legal in the US, although VERY rarely seen. Unlike a MPH speed limit, the numeral is enclosed in a circle, and labeled km/h under the circle. We share land borders with two countries who use metric speed limits. Canada does not require units on every speed limit sign, but near border areas, they place km/h placards under the sign as a reminder to Americans (I’m not sure about Mexico). An American driver will never see kph in his car or on a road, yet automotive journalists use ONLY the incorrect kph, when they can see for themselves the km/h on the speedo of every vehicle they write about. Who knows whether they have a deliberate goal of confusing the public, but they have that effect. It will be a long haul to adopt metric on US roads, but having journalists not confuse people would help, and having them confuse people can only hurt.

    Weather: The National Hurricane Center uses “KM/H” in their hurricane forecasts (the whole forecast is upper case), but journalists change it to kph. So you see an apparently different unit when you look at NHC’s website vs your local newspaper website. Perhaps not a great deal of confusion, but at least some confusion.

    I certainly would not object if a few kph crept through. However, the situation here is that if km/h appears in the media, an editor failed to do his job. Incorrect usage is institutionalized by the AP Stylebook, the correct km/h is not permitted. I feel the deliberate confusion outweighs “using metric at all.” However, I respect that there can be multiple opinions on the matter. I shall continue to flog the issue at the USMA site; here, I will bow to the general consensus.

    Does the press misusing metric help or hurt the cause of metrication?


  32. Hi John

    I do agree with your opinion on the notation – the use of the letter ‘p’ in these abbreviations are a hangover from the old days before the ‘/’ became standard notation. Certainly, when I was at school in the 1980s we were taught to use the ‘/’ in all units, which were of course metric. The only ‘modern’ unit I can think of that has retained a ‘p’ is ‘bps’, for data transfer (nowadays preceded usually by k,M, or G). And of course the very infuriating ‘dpi’ for printer resolution

    Does anyone remember ‘Top Trumps’? They were child card games in the 1970s, you were dealt a hand of cards from a pack all based on the same themes eg ‘Military Fighters’, ‘Civil Aircraft’. Each card had a set of data all based on the same parameters. You had to try and win cards off your colleagues by choosing a parameter that you thought your card could do well on. For many of us, this was our first contact with metric, and we did not know how to ‘say’ the ‘/’ so we used to call it ‘stick’ or ‘slash’ if we were calling out speed.

    Finally John, I see this notation is a real passion of yours. While I understand that, in the UK I fear that such an argument would marginalise metric supporters even more than we often are at the moment. You only have to read the reports from the National Measurement Service to realise that the fact Britain is officially metric is not something we shout about! While I am slightly perturbed that the Science Correspondent of a quality newspaper has got the notation wrong, I am more concerned that an astonishing number of papers still use imperial notation as the standard on most issues. Even the socialist Daily Mirror (which usually is a supporter of Labour, the more metric friendly party) referred to temperatures in F the other day. Thats more worrying to me!


  33. @John Steele, @michdung

    For me the significance of ‘km/h’ rather than ‘kph’ is that the latter is too reminiscent of ‘mph’ which makes it seem a superficial alternative to imperial. It also obscures the difference between an abbreviation and a symbol (an SI symbol is language independent whereas an abbreviation is language specific).

    I think that part of the problem is that people (in the UK) think of measurement as nothing more than a collection of units and see nothing odd in mixing metric and imperial even in the same sentence. I think this is because they are used to things like stones and pounds where there is no obvious reason for the ratio between them. It’s a case of what you’ve never had you don’t miss. Thought of in this way, the metric system is nothing special, merely different and a burden to have to learn it.

    Therefore we need to emphasise that metric is based on a radically different approach to measurement and to encourage people to break with old habits. If we try to make it palatable by cloaking the SI in imperial style conventions it becomes counter-productive.


  34. Phil hits the nail on the head. The huge advantage of the SI is its coherence and rational structure.

    The Imperial set of units (not at all a system) vs SI reminds of the comment I read somewhere that Sir Francis Crick made about the difference between physics (which he studied in college and used to invent a new mine effective against mine sweepers during WWII) and molecular biology (which he took up after the war):

    “Physics is a set of principles; biology is just a collection of mechanisms!”

    He apparently said this in a bit of frustration. 😉

    The same can be said of the SI vs Imperial, I daresay.


  35. Regarding the Surrey Herald story about the lack of metric equivalent warning signs at the low railway bridge, I’ve emailed the council pointing out the Traffic Signs Manual (Chapter 4) recommendation which makes clear that metric signage should be installed on this road:

    “7.8 Metric heights may be shown in addition to imperial heights at any bridge. This is recommended for all bridges on main routes and on roads used frequently by foreign drivers.”

    The road in question is an A-road and is evidently used frequently by foreign drivers, so the only objection they can come up with is one of cost. If they do pull that one, I’ve asked for their cost estimate figures, which, if not forthcoming, can easily be obtained via FoI. It doesn’t matter if they’re a) accurately and tellingly low or b) blatantly and outrageously inflated; they’ll still make for a damning follow-up article for the Surrey Herald.


  36. If there’s a member of the UKMA living near this low railway bridge in Surrey, they might consider taking a leaf out of the ARM’s book, get some well-made adhesive white reflective patches made up stating the clearance height in metres (probably 2.9m would be best in this case) and the imperial value (9′ – 9″) underneath. Then go and “fix” the offending signs. Invite the paper to come and take photos too, proclaiming how locals find themselves forced to do the council’s job for them and address the actual problem.

    You couldn’t get taken to court for vandalising the sign as the “corrected” sign would be as compliant with TSRGD as the old one ever had been.


  37. Maybe it’s because I was a ’60’s radical growing up (in Ohio and Chicago), but I just LOVE Wild Bill’s idea. 🙂


  38. As a rider to the previous post – is the following story referring to the same bridge? See URL

    If so, this happened on the 18th Aug, only 10 days after the previous “stuck truck” story!

    It may be possible to persuade the local paper to get behind a “citizens’ crusade” to get the signs changed, If anyone tries to initiate such a campaign, try to make sure the paper doesn’t repeat the comment it used in its 8th Aug story about suggestions to replace the signs with “more euro-friendly versions in metric”.

    The “crusade” if there was to be one must emphasise how the change will benefit the locals, not Johnny Foreigner. Avoiding having a truck stuck under the bridge every fortnight should be enough, you’d think!

    Nothing is likely to get the people of Surrey less interested in a proposal than to link it with any claim that it is done to “aid Europe” in any way!


  39. Whilst we appreciate the sentiment of Wild Bill, UKMA have always declined to stoop to the level of so-called ‘ARM’.

    If we were to take any action it would be to write to the authority concerned urging them to add a metric sign in accordance with the provisions of TSRGD and encourage local people to do the same.


  40. I for one do not agree with “Wild Bill”

    As far as I can see, he is advocating using an imperial measurement that is accurate only to 3 inches and converting it to metric. This is a recipe for disaster.

    There is a set protocol (which I cannot be bothered looking up) for measuring bridge heights in metric and then working out the safe height which is then displayed on the sign on the bridge. For UKMA to do this, they would have to accurately measure the bridge height, thus putting themselves at risk on busy roads.

    To me, it’s a no-brainer. UKMA should not accept conversions of imperial appoximations, and should not attempt to measure bridge clearances themselves. The letter-writing approach is far better.


  41. Philh says: “UKMA have always declined to stoop to the level of so-called ‘ARM’” – well, it doesn’t have to be official UKMA policy to do such things, but there are occasions where adopting a leaf from the enemy’s playbook can be useful.

    Ken Cooper says: “As far as I can see, he is advocating using an imperial measurement that is accurate only to 3 inches and converting it to metric. This is a recipe for disaster.” Actually, Ken, I agree that such a tactic would be sub-optimal, but it wouldn’t be “a disaster” because it would result in the bridge being legally correctly signed in metric of sorts.

    Yes – the right thing to do would be to measure the bridge, and apply the proper legal procedure for generating a metric height sign. But if whoever did it made a mistake, they would then find themselves legally responsible for any accident that could be blamed on the metric sign. That would not be good – such responsibility should be taken by the local authority – that’s what they are there for.

    So my sub-optimal “convert the imperial height to metric and round down to the nearest 0.1m” generates a legally-safe metric sign. Yeah – possibly it might have flagged a height maybe 0.1m higher if the correct procedures were followed from scratch and the bridge happened to be of a suitable height, but surely safer to do it the other way?

    Letter writing is probably the right route to go. The question is, to whom do you write? The local authority, who have already indicated that they’re not going to act? Or the local paper, who might increase their profile (and their readership) on the back of starting a grassroots uprising?


  42. @Ken,

    I am not suggesting that citizens paint their own signs. However, I stumbled across the “set procedure” while looking up something else in the traffic sign regulations. It was so complex that it strike my fancy and I made note of it. To paraphrase:
    1) Measure the actual height. It is permitted to adjust this for future repaving and I don’t remember that part. Using the actual or adjusted height:
    2) In Imperial, the (possibly adjusted) measurement is truncated to the lower multiple of 3 inches, then 3 inches is subtracted. This ensures clearance of at least 3″, no more than 6″.
    3) In metric, it is truncated to the lower decimeter, and one decimeter subtracted. Thus the clearance is 0.1 – 0.2 m. They expressly recognize that this is not the same value(being nearly 4 – 8″ clearance).

    Based on this procedure and the 9’9″ marking, the actual or adjusted height must be at least 10′ and possibly almost 10′ 3″. The corresponding metric marking would be at least 2.9 m and possibly (at the upper end of height) 3.0 m. A marking of 2.9 m would be “safe” but possibly too restrictive. Only measurement could resolve that uncertainty.


  43. Dear Wild Bill

    As far as UKMA are concerned the enemy is the Department for Transport with their refusal to go metric, not some sad bunch of vigilante nutters.


  44. I agree that DfT is the real culprit here. But there is a germ of a good idea (I think) from Wild Bill.

    How about someone standing near the bridge with a sign that says “Bridge strikes cost us £xM/yr” and another sign attached to the side of it showing what the metric height restriction sign would look like with the words underneath “and this sign here would help prevent them!”

    I’d be glad to volunteer to hold up such a sign except for the fact that I’m sadly located a few megameters too far away at the moment (Seattle, WA, USA).

    What do folks think? This could be useful for garnering some publicity for the issue.


  45. If UKMA considers any type of action to “embarass” DfT into dual signage, this page may be of use:

    It has a list of 11 brifdges struck 10-18 times in the past year. They would be good candidates to consider whether they are signed in Imperial only or dual, and whether dual signage results in a reduction of strikes.

    Some of the information links on the right-hand side are useful too. There have been around 1500-2000 strikes per year in the UK at a cost of around 4000 pounds per strike. For locations struck 18 times per year, it would seem that ANY reduction would pay for a sign. Another interesting tidbit was that bridges with permitted heights of 2.5 – 4.5 m account for the majority of the bridge strikes. “Unrecorded” was more common that heights out of this range.

    In my Google search, I encountered the phrase “truck eatting bridge” a few times. Who could resist that? I found bridges in Iowa, Massachusetts, and Ontario, Canada with that nickname. Canada publishes the name and address of the driver. That bridge seems to be mostly struck by Canadians who should understand the metric markings. The bridge in Iowa has been struck over 1700 times in 45 years but, with HUGE signage, is down to about 12 times per year. The two US bridges are far enough from the border that most of the drivers are probably American, but no way to tell. I think the point is that low bridges get hit and signage can’t completely solve the problem. It may help. Over-reliance on GPS and driver inattention may be bigger factors than the units on the signage.


  46. Excellent find, John! Thank you.

    I would imagine the ideal situation is when there is a single spot in the cab right above the driver with a single set of dimensions (in metric!) that the driver could glance up at and then quickly compare with the restriction sign posted (again, ideally just in metric) so the driver could immediately see if the value posted on the sign is smaller than the value posted above their head in the cab.

    Pending such an ideal world, dual signage (as proposed by the previous DfT administration) would be an important step forward.

    Perhaps a good publicity campaign emphasizing the saving of money (after all, it’s the Tories who are in charge now!) will put the squeeze on Philip Hammond and the DfT to relent and post the additional signage.

    Shall we give it a bash then?


  47. “Shall we give it a bash then?”

    Oops, unfortunate choice of words there Ezra 🙂


  48. Thanks to the modern wonder that is Google Streetview, I decided to “pop down” and take a look at the offending bridge mentioned a few times above – despite living about 300km away. I must say, if the local council think that it is “properly and legally signed” then I don’t agree. Take a look:,+Woking&hl=en&ll=51.349606,-0.48209&spn=0.007639,0.018647&sll=-34.016242,18.457031&sspn=41.434851,76.376953&vpsrc=0&z=16&layer=c&cbll=51.349886,-0.482244&panoid=dG4ogRIXAfj3PWOadfZJgQ&cbp=12,176.28,,0,8.49

    From this side the bridge is deceptive. Did anyone notice the small “9ft 9in” warning triangle under the tree on the left, immediately after the left-turn junction? I didn’t see it the first couple of times. From here the bridge looks quite normal, but in the shadows under the horizontal concrete span in the distance is a smaller brick arch that is the actual problem. Move up closer and you’ll see what I mean.

    It’s more obvious from the other side:,+Woking&hl=en&ll=51.348976,-0.481746&spn=0.007639,0.018647&sll=-34.016242,18.457031&sspn=41.434851,76.376953&vpsrc=0&z=16&layer=c&cbll=51.349086,-0.481805&panoid=JX5EWzfPNSG90C_wge7DQg&cbp=12,335.38,,0,3.34

    The advance warning triangle on this side is just as difficult to see (you’ll have to back up the road a bit to find it, again hidden under some trees, and tilted at an angle away from the road to make it even less visible).

    What’s extra funny is that on the opposite side of the road from the advance warning triangle is a car showroom (Grange Cars) with an overhanging canopy signed in metric-only (as is becoming the norm here I’ve been pleased to notice). No-one other than the DfT believes that British drivers can’t understand metric signs!

    But I digress.

    UKMA might choose to point out to the council that the advance warning triangles should be type 531.1 warning of an arch bridge, not just an unspecified height limit as it is now. The bridge itself should be marked up with height restriction chords as shown in diagram 532.2 on page 33 of chapter 4 of the Traffic Signs Manual. And yes, missing out the metric triangles may be technically legal, but it could be regarded as negligent behaviour considering that this is an “A” road with a history of bridge strikes at this site, and that paragraph 7.8 on page 29 *recommends* metric signage on all main roads, regardless of where the drivers of any trucks might come from.

    Paragraph 7.20 on page 34 of the same manual suggests that in the case of a composite bridge (which this would appear to be) then black and yellow suspended plates should be hung from the deceptive concrete beam on the northern side to highlight the hidden arch within, and to strike a truck *before* the actual bridge does!

    I don’t think the council have paid any attention to the Traffic Signs Manual. What do you others think? A URL for the traffic signs manual BTW is:

    Click to access trafficsignsmanualchapter4.pdf

    BTW, I belatedly notice that my suggestion of locals taking action with sticky labels had already been suggested by Michael Glass on 2011-08-12. Sorry, Michael – I should have read the historical articles better before reposting the same suggestion.


  49. Excellent posting, Wild Bill … and all counts (information and suggestions).

    It also seems to me that such a narrow-looking bridge should have a width restriction posted as well. For instance, we allow wide loads here in the States and I presume certain HGVs could also be too wide for the bridge.


  50. Laudible though the above suggestions may be, UKMA are not experts on road signage. Our sole concern is that the absence of metric indications represent an element of risk in cases like this. Whilst we can easily point out that current TSRGD permits their inclusion it might not be wise for us to go beyond that because it will only cloud the issue.
    For us the issue is not how conspicuous or accurate the existing signs are but the fact that some drivers will not understand their content even if they do see them sufficiently well in advance.
    It is of course a useful example in a wider sense, namely that the metric option should be the norm not the occasional exception and we will use it to make our point.


  51. @Wild Bill
    Good detective work. If you move closer, the interior bridge is marked as an arch with the yellow and black border. However, it is so deep in the shadows it may not be apparent to a driver out in the sun.
    (You have to move view into those shadows so the camera exposure adjusts)

    As an American used to LHD vehicles, I note than only half the chord line is marked (from center to chord). In a LHD vehicle (and this may affect foreign lorries), it would be a little difficult to align yourself with the chord markings. I note on the far side, the bridge has suffered a visible strike exactly where I think the missing half of the chord line marking should be. My understanding from browsing the traffic signs manual was that the full chord over which the vertical clearance applies should be marked.

    The markings may or may not be minimally compliant with the law, but when there is a repeated problem, the best practice that the law allows seems more likely to help than being minimally compliant. The local council should be looking at how to improve the markings.


  52. The point previously made about consistent and universal signage is key here. Any driver, whether English, Welsh, Scottish, Irish, or from the Continent should be able to count on what to expect in terms of signage and warning when the approach a bridge or underpass. This means dual signage (Imperial and metric) everywhere.


  53. I must admit that I find para 7.8 of the traffice signs manual interesting:

    “Metric heights may be shown in addition to
    imperial heights at any bridge. This is recommended
    for all bridges on main routes and on roads used
    frequently by foreign drivers. …”

    I think one can draw the conclusion from this that the Department for Transport do acknowledge that not all drivers understand imperial!

    Thank you Wild Bill for drawing attention to that part of the document.


  54. Since the traffic signs manual mentions the option of showing metric heights at any bridge, does it have anything to say about showing metric widths or metric lengths?

    For example, a bridge that is located over a low point between two hills should (I would imagine) have posted a length restriction. Similarly, narrow one-lane bridges would seem logically to need a width restriction posted. The reasoning behind posting metric heights should call for metric signage in those cases as well — I’m just wondering if the traffic signs manual mentions those situations.


  55. Thank you to just about everyone for your appreciative comments recently! In answer to John Steele’s comment about the chord line, from my reading of the Traffic Signs Manual (TSM) then that chord line should reach from side to side of the the centre. Not just to the one side as happens here.

    To Philh: I never thought there was doubt in the DfT’s mind about the need for metric signage, that’s why metric height has been an option since (according to wikipedia) TSRGD 1993, and the metric width option has been there since TSRGD 2002. The problem in this case isn’t the DfT (for a change!), this time it’s the local authority. They are the ones who get to choose whether the available metric options get used or not and here they seem to be stubbornly refusing to take up on it.

    To Ezra: unless I’m mistaken,, there is no legal option for a metric length limit to be displayed on any sign in the UK.

    That said, I do believe that a local authority can get permission from the DfT for any sign saying any thing – they just have to get it cleared on a case-by-case basis. But that’s a PITA for them, and so the usual situation is that only signs meeting the current TSRGD ever get put up, because they need no special authority for any of those. So you could have a metric length sign by special arrangement…. I don’t think I’ve ever seen a length-limit sign “in the wild” though.


  56. The recent DfT decision is irrational, inexplicable and incomprehensible. The response to their own consultation about mandatory dual signs for bridges showed a net saving of £1.8 million over ten years and strong support for the change from many stakeholders. They have still not explained why they dropped this proposal nor are they interested in adopting the Vienna Convention for height and width restriction signs.

    The Department for Transport recommends that local authorities use metres on restriction signs but despite the problems with the grossly disproportionate bridge strikes by foreign lorries, it is a scandal that local authorities are still putting up imperial-only restriction signs with the endorsement of the DfT. Had the DfT made it mandatory to use metres instead of optional when metres were first introduced on restriction signs, it would have cost no more money and we would not have this problem with the excessive number of bridge strikes by foreign lorries.


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