Britain’s new Highway Code. Updated but outdated – a victim of the measurement muddle

The new Highway Code is an example of the consequences of the Britain’s measurement system muddle. Its mixture of units from the imperial and metric systems brings confusion, when clarity should be a foremost requirement. The UK Metric Association (UKMA) has looked forward to the completion of the metric changeover, and produced a simplified, metric version of the Highway Code to illustrate the clarity that one system makes possible. (Press release issued on 27 September 2007.)

HMSO will publish a new version of the Highway Code on 28 September. The updated version of this best seller has to steer a path through the UK measurement muddle. It must meet the needs of an older generation who have been taught only in imperial measurements, and perhaps now rarely need to refer to the Highway Code. But it must also be relevant those who are more familiar with metres than with yards, feet and inches, in particular younger road users and those who grew up abroad. Members of these groups, preparing for their driving tests, are among the Highway Code’s keenest readers.

UKMA welcomes the new Highway Code, but considers that some parts feel outdated as a result of the need to target two very different audiences. This problem arises from failure of the UK to complete the transition to the metric system, begun over 40 years ago. In that time, many UK industries have made the changeover, including construction, manufacture, engineering and pharmaceuticals, and metric has been taught as the primary system of measurement in schools and universities since the 1970’s. However, the changeover of traffic signs, planned for 1973, has been repeatedly postponed.

UKMA has looked towards the completion of the UK metric changeover, and produced a modern version of the Highway Code, using only metric measurements, to illustrate the clarity that one system makes possible.

The full text of UKMA’s metric edition of the Highway Code can be found at

A glance at the comparison of the tables of speed limits and stopping distances, before and after, illustrates what can be achieved. We have also looked at examples of traffic signs in the new Highway Code to show how these might change.

Said UKMA Chairman Robin Paice:”Every country needs a system of weights and measures that everybody understands and uses for all purposes. Nobody needs two systems. The Irish Government showed in 2005 that the UK could easily put the muddle on the roads behind us, yet we continue to fall further behind. Completing metrication is in the national interest, as difficulties with the Highway Code demonstrate, and it is time that the UK Government acknowledges this and shows some leadership.”

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26 Responses to Britain’s new Highway Code. Updated but outdated – a victim of the measurement muddle

  1. George Carty says:

    For motorway exit approach signs I'd suggest replacing "1 mile" with "1600 m" and "1/2 mile" with "800 m" (NOT "1 km"). I like the way the German Autobahn signs use metres rather than kilometres...

  2. Martin Vlietstra says:

    This document shows how clumsy the current Highway Code is in trying to handle both metric and imperial units. One area that I think should be looked a little more carefully is the way in which shorter distances are represented.

    I would prefer to see metres rather than kilometres being used on all advance off-ramp warning signs. In general, I believe that the choice of metres or kilometres should be consistent for each class of sign. In this instance, the values 500 m, 1000 m, 800 m and 1600 would cover over 90% of such signs. There are a few instances where values that are greater than one mile are currently used, but I have yet to see an instanced where more than two miles are used. In such cases, the distances would go up to 3000 m, but I do not see this as a problem. Using metres rather than kilometres would be consistent with Continental practice.

    The other area that is not addressed is how to convert fractions of a mile. Currently the TSRGD permits fractions of a mile for distances up to 3 miles. I suggest that the following be permitted:

    Up to 2 km - round to the nearest 0.1 km
    Up to 5 km - round to the nearest 0.2 km
    Up to 10 km - round to the nearest 0.5 km
    Thereafter round to the nearest kilometre.

    This will ensure that all distances that are over one kilometre will be denoted to at least 10% accuracy.

  3. Alex Bailey says:

    This is a great example of how much clearer and less cluttered things can be if only one system of measurements is used - removing the need to "explain" the different units makes both text and graphics flow better. It's a real shame that we're still a little way off seeing this in the published version as it would be a lot easier to read.

    The challenges now will be to try and influence the DfT to recommend the use of metric road signs where legal in the upcoming changes to chapter 3 of the Road Signs Manuals (the manual used to guide local authorities on how road signs should be done properly - consultation at and then to try to influence them to increase and improve on the use of metric in a new version of the Traffic Signs Regulations and General Directions.

  4. Dave Brown says:

    It seems ludicrous to me that we still feel we need to consider "the needs of an older generation who have been taught only in imperial measurements". The metric system was adopted in this country several decades ago, and the government put some effort into re-educating people in the 1970s. Since all official government business, trade and comerce is now conducted in metric units I don't think it unreasonable to expect people to take responsibility for educating themselves about the system. On the other hand, we have no responsibility to educate ourselves in obsolete yards and miles. Yet the government expects us all to be conversant with those units in order to use the roads. That is national disgrace.

  5. Phil Hall says:

    For me one of the greatest benefits is the straightforwardness of scaling between shorter and longer distances. A sign saying 1500 m for example can be read as 1.5 km depending on whether you wish to think of travel time in minutes/seconds or hours.

    When I see a sign on a motorway or trunk road that says the next junction (the exit I'm looking for) is 1 mile or half mile, I immediately convert that to 1600 m or 800 m so I know that the first count-down marker is 1300 m or 500 m up ahead. At this point I get into the inside lane and slow down so my speedo indicates about 60 mph, which is a little under 100 km/h so I know I'm going at about 25 m/s or 4 seconds to travel 100 m

    That kind of reckoning is not easy with miles and yards.

  6. Symbols On Signs
    To illustrate a point that Alex Bailey made above; it is sad that the wrong symbol for tonne is used in this new edition of the Highway Code.
    The correct symbol for tonne is 't', it is NOT a capital letter 'T'.
    Despite some local authority transport workers being aware of this error for many years, new signs showing 'T' are still being put up.
    The symbol 'T' is for the unit 'tesla'. This is the SI unit for magnetic induction, magnetic flux density, and magnetic polarization.

    Perhaps the capital T has an attraction!
    Please help and get this message across, that the symbol for tonne is a small letter t, the consultation is at:

    Thank you, SI Metric-Matters/Philip Bladon

  7. Martin Vlietstra says:

    If anybody is replying to the consultation, they should remember that the authors of the Traffic Signs Manual cannot change the law - they can only implement it. However 17(10) of The Traffic Signs Regulations and General Directions 2002 states:

    "Where an upright sign indicates a weight in tonnes using the symbol "T", that symbol may be varied to "t"."

    Given therefore that "T" is the incorrect symbol for tonnes and the legislation permits the use of "t", it is within the remit of the authors of the Traffic Sign Manual to use "t" rather than "T".

  8. Alex Bailey says:

    In addition to Martin's note about the use of "T" and "t" for tonnes, the "Traffic Signs Regulations and General Directions 2002" also allows the use of metric on height and width signs but does not make it mandatory.

    Chapter 4 of the "Traffic Signs Manual" recommends that metric height signs be used on roads where foreign drivers are more likely, but no similar recommendation exists in the new chapter being consulted on and this is something we should ask to be considered.

    It would also seem to make sense to recommend the use of metric where legal and possible anyway for two reasons. 1) To cater for those of who were metric educated and 2) to save money and time in the longer term and avoid having to replace existing non-metric signs sooner if/when metric does become mandatory!

  9. Ezra Steinberg says:

    The one oddity I did not expect in these regulations is that tramcar speed limits are in kilometres per hour only!

    Too bad they can't see the value of extending this to the motorways.

  10. Daniel Jackson says:

    Ezra Steinberg Says:

    October 4th, 2007 at 21:45
    The one oddity I did not expect in these regulations is that tramcar speed limits are in kilometres per hour only!

    Tramcars are not operated by just anyone. The tram cars are most likely made for the international market with only one type of speed indicator for simplicity. There is no worry that some person claiming not to know metric would be operating a tramcar. If a tramcar operator claims not to know metric, he can be replaced by someone who does.

  11. I wish we could get rid of obsolete units once and for all. Councils are supposed to be reviewing speed limits across the country so this would be an ideal time to metricate them. Even just doing Northern Ireland so that the whole of Ireland would be consistent would be better than nothing.
    One problem that remains is that we would still use km/hr for speeds. This is a sensible unit for journey planning but not for safety where metres per second would give a much better idea of a vehicle's speed and stopping capability.

  12. Sean Wisehall says:

    All these imperialists get on their soap boxes about public safety being an impasse to adopting SI signage. They use the same arguments for driving on the left. Well guess what? Sweden switched in one day!
    They can't seriously think that leaving slapdash signs everywhere is somehow LESS of a concern to safety than a quick, painless switch.

    What I see here is a lack of political courage. Yet again we are seeing monumental long term costs imposed for saving a days hassle. At some point all the signs WILL be Metric. Should we drag this out any longer? Who is this benefitting? Should everybody pay for the stubborness of a few dinosaurs?

  13. Ezra Steinberg says:

    I think Sean Wisehall makes an excellent point.

    As I've mentioned elsewhere, you can easily shed light on the speciousness of the arguments of the BWMA and similar folks by asking them what the UK should when the day comes that the USA starts metricating. Suddenly, all the opposition would vanish in a flash and the UK government would be metricating in a nanosecond! So much for any notion of "Imperial forever".

  14. Sean Wisehall says:

    Ezra, you are exactly right. Once the US goes metric those imperial vestiges will fall faster than a house of cards. Fringe groups like the BWMA espouse "choice" yet gloat every time US policy does not give us a choice to use SI. They realize that its ultimately the muddle in the US that keeps theirs going.

  15. George Carty says:

    Another point - I hope that the "km" markings on distance signs will be removed once metrication is completed, as I think they look ugly (current signs don't have "m" for miles on every distance).

  16. Dave Brown says:

    If you ask the DfT (via your MP) why we don't go metric on the roads, the answer used to be that >50% of drivers were educated before metrication, and so not changing would affect fewer people. Now that's no longer true, they've changed their excuse and say that it would be too expensive. Of course the change will have to come eventually, and it's never going to get any cheaper. In fact, every speed limit sign erected in the mean time adds further costs to the eventual change-over.

    UKMA should push for a moratorium on putting up new speed limit signs until after the switch. The government would of course resist this as they are still trying to clamp down on speeding by creating more speed limits; and this would create an opportunity for public debate.

  17. Daniel Jackson says:

    Dave Brown Says:

    "If you ask the DfT (via your MP) why we don’t go metric on the roads, the answer used to be that >50% of drivers were educated before metrication, and so not changing would affect fewer people. Now that’s no longer true, they’ve changed their excuse and say that it would be too expensive."

    To know for sure how much it would really cost, all one needs to do is look at the cost the other nations endured when they metricated. most were able to come up with unique plans that actually reduced the costs and were able to make it fairly cheap.

    The excuse about >50% of drivers were educated before metrication is really saying that British citizens are ignorant and can't learn anything new. How do they justify the fact that the other countries that metricated also had a population not educated in metric, and yet the people adapted with zero consequences?

    The only real reason to keep the signs in miles and yards is because it gives the imperialists hope that imperial is not only dead yet, but there is a chance, albeit slim, for an imperial revival. Road signs in miles are a visible sign that imperial is still alive and kicking in the UK.

    Another point of interest is how many of the road signs are correct to their imperial designations? How many road signs are placed at rounded metric distances with the miles being an approximation of that distance? How many signs stating a distance in yards is really that distance in metres? Eg. How many 200 yard signs really are at a 200 m distance? Who would really know they are right or wrong?

  18. Sean Weisthal says:

    "yard" marked signs are actually placed quite accurately to what the sign says - as is confirmed by DfT manuals.

  19. Martin Ward says:

    On many road works signs, "yards" do in fact mean metres.

    See Traffic Signs Manual Chapter 8

    e.g. page 74 states:

    "The principles for the approach signing are: ...
    a "road works" sign with supplementary plate "800 yds" placed on the near side 800 m in advance of the works lead taper;
    a "road works" sign with supplementary plate "400 yds" placed on the near side 400 m in advance of the works lead taper; and
    a "road narrows" sign with supplementary plate "200 yds" placed on the near side 200 m in advance of the works lead taper."

  20. Ezra Steinberg says:

    The same page says that an approach sign is to be placed at 1600 m ahead of the road work with a supplementary plate of "1 mile".

    Is the rest of the manual similar to this? If so, metric distances are "wired in" throughout. In that case, all distance signs should be metric with Imperial overlays awaiting the eventual M-Day.

  21. Sean Weisthal says:

    Some documents show distances to exact conversions of metric/imperial, some don't. I have even noticed signs being "paced out".

    Here is one where conversions are made:

    See page 21 for examples.

    You may be interested in how heights are signed-up

    (See pages around 31).

    There seems to be a mix - and a mix between DfT documents.

  22. Sean Weisthal says:

    FYI This more generic document:

    Mentions the trams' km/h speed limit signs

  23. Martin Ward says:

    Ezra, the predominant use of metric in the Traffic Signs Manual reflects the fact that roads in the UK are designed, surveyed and built using metric measurements.

    However, because the display of imperial units continues to be required on road signs, the manual inevitably exhibits a certain amount of awkwardness when it comes to specifying the siting of road signs showing distances - adding complications to the work of road contractors that would be unnecessary if metric signage was used.

    Sometimes "yards" are allowed to mean metres (as is the case for road works), in other cases distances are specified in yards (leaving the conversion to the contractor), and sometimes metric distances are specified for corresponding nominal imperial distances.

    e.g. page 20 of Traffic Signs Manual Chapter 4 has a table specifying the siting of approach signs indicating a reduction in the number of lanes.

    distance legend
    135 m 150 yds
    180 m 200 yds
    270 m 300 yds
    360 m 400 yds
    800 m 1/2 mile

    Generally, a variation of up to 10% is permitted between the actual distance and the distance shown on the sign. So showing a distance of 200 m as "200 yds" would fall within this tolerance.

  24. Harvey says:

    Despite being from the USA and being an Imperialist (Even if it's US customary here), does anyone think that the UK can put its highway code entirely in miles, yards, feet, inches, and miles per hour? After all, the majority of British people prefer Imperial. So if the highway code was Imperial only, would that put clarity. I think so. Now what do you people think.

  25. philh says:

    Dear Harvey

    You want clarity. That is good.

    So why do you want a mess of units like miles, yards, feet, inches and miles per hour? Why so many, especially when they relate to each other with awkward numbers like 12, 3, 36, 1760, 5280, 63360?

    The obvious alternative is to use metric only for both the highway code and road signs. All that would be needed is the metre, kilometre and kilometre per hour. When you consider that kilometre just means 1000 metres it is even better.

    You say British people prefer Imperial. I say it is not as simple as that. They are confused over measurement because of the way things are in Britain. For example I often hear people talk in metres for short distances and lapse into miles for longer distances or talk in inches for smallish measurements and millimetres the very small. How clearly are they thinking?

    If people in Britain were to allowed experience using metric properly, without the imperial clutter and without having to convert all the time they would appreciate its advantages and come to prefer it.

    Yes we want clarity. For that we need a single system that everybody can understand and use. We need metric!

  26. michael says:

    Given that this blog is on the UK Metric Association website, I’m sure you won’t be surprised to hear me say that I think that the Highway Code suffers tremendously by continuing with it’s referral to Imperial measures. The mile, yard, foot and inch are not referred to anywhere in the National Curriculum used throughout British state education. Nor have they since 1974.

    You say that British people want Imperial, but they are not crying out for it. The new Coalition Government has set up a website,, to invite the publics views on matters that effect them. The Metric/Imperial debate has attracted some threads, but the numbers voting show that there is very little real interest. The pro-metric threads have a more favourable response than the Imperial ones. The vast majority of people in the UK shop in supermarkets which all only sell items in metric units.

    In matters relating to the road, I do believe that initially the yard should be replaced by the metre. Signs showing yards are usually positioned to refer to the meter distance anyway eg - many signs show a hazard in 110 yds, 220 yds, 330 yds etc ready to be replaced by 100m, 200m, 300m etc. Many British major routes already have marker boards positioned every 100 metres, and at 500m seperations on the motorways. Yards are a defunct measure in all other aspects of daily life - all athletic events are in metres, fabrics & trimmings etc are all sold by the metre and so on. Metres are also straightforward to convert into miles, using 1600 metres - easier to remember than 1760 yards.

    In the long term, I hope we can get rid of the mile. But with the cost implications in a period of huge spending cuts, coupled with the Conservatives traditional reluctant approach to metrication, I'm not holding my breath.


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