UK pays the cost of failure to implement the Vienna Convention

The Department for Transport (DfT) continues to ignore the clear advantages of the adoption of the international norms for road signage, namely the use of metric units, while potentially preventable accidents occur on our roads.

The UK is signatory to an international road safety convention which requires metres to be used on width, height and length restriction signs, and yet the Government refuses to bring this requirement into UK regulations.

Last month a lorry from the continent was driven through a width restriction in London, rupturing its fuel tank. This caused a reported £100,000 damage to the highway, which had to be resurfaced as a result of the accident. It appears that the driver had failed to understand a sign showing >7′-0″<. It has also been reported on many occasions that vehicles have have struck railway bridges because their drivers did not understand the imperial height limit signs.  British drivers of large vehicles also need to know their vehicles' dimensions in metres as well as in feet in order to negotiate private goods yards signed in metres and also to operate in the Republic of Ireland and on the continent. So it is no wonder that so many lorry drivers are having problems.

These incidents carry a heavy cost to the British taxpayer, insurance companies and the users of disrupted road and rail networks. Yet the addition of metric measurements on height and width restriction signs would incur a comparatively small cost if carried out over a reasonable period of time.

The UK is a signatory of the Vienna Convention on Road Traffic and the European agreement which supplements the Convention, both of which are aimed at achieving greater uniformity in the rules governing road traffic in Europe. They establish road safety standards, providing Governments with a harmonised legal and technical basis for their national highway codes and ensuring a high level of road safety in the countries that implement them.

The Convention has, since 1993, permitted only metres to be used for the signage of vehicle restriction signs for length, width and height. In recognition of this, the UK's traffic sign regulations were altered to permit the use of metres on such signs.

Sadly, the UK has failed to implement in full the signing conventions. It is committed to requiring metres to be used on vehicle dimension signs, yet instead it has left each local highway authority to decide whether it will use metres in addition to imperial units. The Traffic Signs Manual Chapter 4 of 2004 states that signs in metres should be used â??on main routes and on roads used frequently by foreign driversâ?? without giving guidance as to what constitutes â??frequent useâ??, let alone explaining the flawed logic which suggests that foreign drivers on main roads can't be expected to understand signs in feet whereas as soon as they turn off a main road they can. The use of satnav has also made "frequent use by foreign drivers" more difficult to predict.

The DfT has argued in recent years that the UK can not afford metric road signs, and appears unwilling to reconsider, even when there is an international obligation to provide such signs and it can be shown that this would be cost effective.

22 thoughts on “UK pays the cost of failure to implement the Vienna Convention”

  1. This is quite startling news.

    I also find it hard to believe that there are so many signs restricting width, height and length (compared to speed limit and distance signs) that the UK cannot reasonably begin to convert all those signs over time to at least include the metric equivalent.


  2. Not only does the sign [ 7′ 0″ ] not conform the the Vienna Convention on Road Signs, but it is also in breach of the EU Directive on weights and measures in that the EU directive states explicitly that the symbols for feet and inches are “ft” and “in” respectively (having stated that single and double apostrophe are the symbols for minutes and seconds of arc respectively). The EU directive is consistent with the recommendations of both ISO and the CGPM.The UK legislation that implemented the EU directive conveniently omitted the symbols for the mile, yard, foot and inch from its text. Maybe the Whitehall mandarins thought that they were being clever, but the European Court has since ruled that “that member states could be liable to pay damages to individuals and companies who had been adversely affected by the non-implementation of a directive” (See


  3. In my experience, non-metric width restriction signs are still the norm at road works on motorways and major roads.

    According to the Sparks Report, published in 2007, more than 3 million foreign registered vehicles enter the UK each year, 140,000 of which are present at any given time. Across the whole of the UK, foreign registered vehicles travel a total of almost 5 billion kilometres each year.

    Click to access Sparks_report_final_230707.pdf

    How much more frequently do our roads need to be used by vehicles from metric-only countries before the Department for Transport acknowledges the need for standard metric road signs?


  4. A question. If imperial-only road signs confuse overseas lorry-drivers and increases the number of road ‘incidents,’ would switching to metric-only decrease this number, or increase it? I ask this because in 2003 I commissioned IPSOS-RSL to carry out a national survey of British adults aged 15 and over, into their ability to estimate sizes and distances. One of the findings was that 71% of the public – and 54% of 15-19s – are unable to estimate their own height in metres. On that basis, I’d say that the safest system, from the point of view of fewest crashes, is dual measures; then imperial-only; and then, quite a long way behind, metric-only. As I understand it (and correct me if I’ve got this wrong) the current law allows for dual-measures signs.


  5. I think the answer to Warwick Cairns is that it is the persistence of two rival systems in the UK that is the problem. Foreign drivers in the UK have no incentive to understand imperial measures since they will only encounter them for short periods while in the UK and then return to “normal” when they go home. However, if imperial measures were phased out in the UK drivers would soon adapt and become familiar with metric values since they would have no reason to return to imperial measures. The crutch would have been removed.

    When Ireland converted to metric speed limits in 2005, the Gardai warned that they would have no sympathy for drivers who claimed not to understand kilometres. The change went smoothly with no discernible increase in accidents.


  6. In reply to Warwick Cairns, it would be more accurate to say that some road signage requirements specify (1) imperial only signs, some (2) metric only and some (3) allow (but do not require) dual marking. Examples: – (1) distances in yards and miles, (2) weight limits in tonnes and (3) height and width restrictions. But there are all sorts of inconsistencies – for instance UK vehicle construction regulations only require high vehicles such as double deck buses to display their height in feet and inches in the cab – not much use when they travel abroad. Another example of the absurdity is that London’s “bendy buses” carry warning signs displaying their length in metres – running on roads around the capital carrying length restrictions shown in feet and inches only. Whichever way you look at it, a muddled, inconsistent application of two systems does not help anybody.


  7. In response to Warwick Cairns, I’m guessing that a good proportion of people in your survey couldn’t estimate distances well in either unit, as with all things it’s what you’re used to. However what we come down to here is the old saying “jack of all trades, master of none”. While we continue to use a mish-mash of two systems people will continue to be confused whether it be in the supermarkets or on the roads – and in some cases will get ripped off (such as an arena in Nottingham who have got away with selling under-sized soft drinks for years because they price in oz but dispense in ml).

    Quite simply, unless people have an opportunity to use metric in every day life they will never learn to use it properly. This wastes our education and hurts our industry… it is also a major factor in safety in many areas, not just on our roads!


  8. Warwick is quite correct in saying that the traffic sign regulations *allow* dual measures for height and width, but according to his own logic they should be *compelled* on grounds of current safety considerations.
    It’s noticeable that those who have been physically expressing their objections to the use of metric on road signs have tried to enforce imperial only.


  9. I finally found the official Irish Republic web site for road signs from the Road Safety Authority:

    Note the updated height restriction sign (about one-third of the way down the page) with the more European-looking design (like the other signs shown) rather than the older USA style.

    Only height restriction is shown (though I assume width is the same but with the arrows on the left and right; not sure what they do for length).

    Imperial appears first followed by metric with both equally prominent, which looks to me like the design used in the UK for signs marked in both kinds of units (if I’m remembering correctly).


  10. It baffles me that more recently the cost of conversion has been used as an excuse for not moving forward… but with a little thought all of our road signs (with the exception of speed limits) could be updated over time with little or no additional cost. The main factor is education – and as I’ve already said, if people are given the opportunity to use metric they will quickly get used to it.


  11. If I’m not mistaken, there have been some communities that had erected dual unit height/width signs in the UK. Even though totally legal, a particular anti-metric group has painted out the metric portion. This act of vandalism should be illegal and the culprits severely prosecuted.

    I wonder if there are any roads in the UK that have experienced a serious accident because of ignorance to feet-inch signs where there was a metric equivalent sign and it was either vandalized or removed.


  12. Alexis quite right.

    One other fact immediately demolishes the DfT’s argument that conversion is “too expensive”. There is a good chance that a very modern, internationally-minded President (Barak Obama) will take office next year with a Democratic majority in Congress.

    If we here in the States succeed in starting a conversion program to metric (hopefully, a la Australia), which will include converting road signs, how long do you think the DfT will take before it decides the UK should adopt a sensible conversion program as well? Suddenly, the “it’s too expensive” argument will magically melt away, I’m quite certain!


  13. If it it true what Mr Cairns says, that over half of our teenagers do not even know their own height in the international system of measurements then that is nothing short of a scandal. What do they learn during their childhood?

    The future for our children will be in a globalized economy where they will need to compete and co-operate on equal terms with people from every corner of the world. If they can’t even communicate basic facts like how tall they are then the UK is going to become a very poor place to grow up, and UK employees are going to be the last choice to have on your global team.


  14. I had an instance when giving private Physics tuition to an AS Level student a few years ago when I asked him to convert his height (six foot) into metric units. I gave him a 300 mm/12 inch ruler and asked him what a foot was in metric units. Rather than read the conversion from the ruler, he measured his foot! It did not occur to him that there were 12 inches in a foot. I do not believe that this was an isolated incident.


  15. As it happens, I discovered via the UKMA’s link to the DfT’s traffic sign manual that metric-only height restriction signs are indeed allowed.

    The catch, of course, is that they must be accompanied by an equivalent Imperial-only height restriction sign that is either above or to the left of the metric-only sign.

    A combined metric and Imperial height restriction sign is also allowed. Oddly enough, however, in this case the metric restriction is placed first (above the Imperial restriction).

    So there we have it: a muddle within a muddle within a muddle.

    Churchill’s words aptly describe the DfT: a riddle wrapped in a mystery inside an enigma!


  16. A couple of years ago I hired a large van. Within minutes I came across a low bridge on a busy road. The height restriction on the bridge was in imperial, the vehicle dimensions were clearly given on the sun visor in metric. Since reversing wasn’t an option given the traffic behind me, my only option was to drive under the bridge with my head out of the window to check the roof of the van didn’t hit the bridge. The idiotic, government-backed dual measurement system in Britain is just asking for trouble.


  17. The more I realise the fact that Britain’s road signs are primarily imperial, the more bizarre it appears to me. The whole world is metric! (Well, except the USA.) I lived in Canada for many years, and witnessed the changeover on the roads first hand (I even had a peripheral role as a member of a sub-committee that established the preferred units and increments). That was 30 years ago, and people in Canada today just don’t even begin to think in miles on the roads. If anyone has watched that program on TV about the truckers driving ice roads in Northern Canada, you’ll know what I mean – even these, perhaps salt of the earth types, but hardly paragons of higher education, will only use m and km. If these people can do it, then so can any Brit. How long do we have to keep on making excuses for government inaction and stupid imperial zealots?


  18. In Australia, the change from Imperial to metric signs on roads was helped by the fact that before the changeover, we had signs that were like the American signs whereas when the signs were metricated, they were made to conform to the International designs. This can be seen in the following clip on Youtube:

    As there was a clear difference in the signs it helped to avoid confusion. It also helped that all the signs were changed in one month, July 1974.


  19. With road signs, the problem with height signs is clearly an opportunity. As a matter of safety, UK clearance signs under bridges must be marked in both metres and feet and inches. Any other arrangement is asking for trouble. Campaign for this change and you’re on a winner.

    There’s another change that would also make sense: metricate the roads in Northern Ireland. It is crazy to have different systems on one island.


  20. can anyone tell me if there is a legal requirement to display height restriction signs? We have recently damaged a van and wonder if we have any rights for compensation?


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