What a UK metric road signs changeover could look like

We have explained the need to go metric, to have metric road signs, and have given many examples of what metric road signs would look like. I also believe metrication is a good time to have a look at signage improvements including clutter removal.  I do not plan on going into too much detail about the changeover, as metrication and road signs have been rather overdone (on this blog). But I do intend on looking at the key points.

Estimates of the cost

The UKMA estimated in its Metric Signs Ahead report back in 2006 that the metric changeover would have a likely cost of £80 million, whereas the DfT who were looking for excuses not to change and hoping to stop the debate, made an overinflated estimate of £760 million.  To put both into perspective, both are much less than the roads budget of £7 billion (this despite an estimated revenue of £43 billion in Road Taxes every year - which is a separate issue entirely).

Even though it is not intended to be prescriptive, I recommend that the UKMA's changeover plan, and the UKMA's suggestions in the Traffic Signs 2.0 booklet, would be good places for the DfT (who would be responsible for the changeover, to start).  I also believe the signage suggestions I have included in my articles are also good places to start.

My points on this article are not prescriptive either, indeed as correctly pointed out, this is from the point of view of an ordinary road user and cyclist, and therefore a layman (and I do not have any operational experience with road signs either), albeit someone who supports metrication and suggests symbolic signage as a means of reducing clutter.  The experts will know how best to carry out the metrication conversion.

Preparatory changes

In my opinion, I would recommend the following being done as preparatory work (which can be done today):

• Where "m" has been incorrectly used to abbreviate mile, replace "m" with "mi" or "miles".  The usage of "m" to abbreviate miles should be made illegal with immediate effect.
• As a temporary step "mi", can added as a permitted variant of "mile" or "miles", or alternatively the misused symbol can be covered up.
• Start replacing all instances of "T" with "t", on weight restriction signs, where "T" (the symbol for tesla) has been incorrectly used to denote tonne.  The correct symbol for tonne is "t".
• As a matter of urgency, start replacing imperial restriction signage with dual unit at least, as there is a safety issue from not having metric restriction signs.  Dual unit should continue to be prohibited from all other signs.
• Imperial-only restriction signs should be prohibited (in other words, reinstating what the previous government was planning).
• Time should be converted from 12 hour to 24 hour (the necessary laws can be changed if required).  This can be done today with no safety issues.

Otherwise these can be started as once the metric changeover has started. Then metrication proper can begin, once the correction of signage is done (or otherwise).

Announcement and metrication proper

The government has to announce plans for metric road signs:

• Preparing for the changeover, in terms of funding, project planning, contracts, needs to be done.
• The following need to be added to the list of authorised units: m and km.  In addition, km/h will replace mph on the day of the changeover itself as an authorised unit.
• The following need to be removed from the list of authorised units: inch, foot, yard, mile. Savings regulations would apply.
• The use of "m" to mean miles should be made illegal, if this has not already been done.  "mi" can be temporarily be added as a permitted variant of "m" until the end of the changeover.
• Only 24 hour time should be authorised. Savings regulations would apply to unconverted signs.
• A date for the changeover to metric speed limits needs to be named:
  
  • The only authorised unit for speeds from the changeover day onwards will be km/h.
  • Taking effect from the changeover day, miles per hour will no longer be authorised.
• The government can require metric-primary imperial-secondary speedometers with km or dual-unit odometers in new cars.  
• Metric-only speedometers and odometers would be required from the day that the speed limit signs are all converted to km/h.
• The start of the distance signage conversion can begin immediately
• Speed limit changeover preparation can begin.
• Stakeholders need to be involved early on in the planning of the changeover.  Effective communication is necessary.
• There needs to be a campaign of publicity, especially in the months leading up to the day speed limits go metric, where there needs to be a shorp sharp campaign of publicity.

Distance signage changeover, as well as implementing the Vienna Convention properly at the same time, can begin gradually, spread out over a longer period:

• Gradually metricate all distance supplementary plates (with an accuracy of 90%).
  
  • Can use m up to 3000 m
  • Between 3 km and 10 km one can use km, and round to the nearest 0.5 km.
  • For 10km onwards, one can round conversions to the nearest 1 km
  • Supplementary plates which show length of a hazard should be made symbolic, for example replace "For 6 miles" with "↑ 10 km ↑".
• Start or continue replacing "T" with "t".
• Start or continue replacing 12 hour time with 24 hour time
• Start or continue replacing "m" (incorrectly used to mean miles) with "mi"
• Once no sign has "m" used to abbreviate miles, the relevant distance signs can be metricated (including motorway exit and services signs):
  
  • For these type of signs, I would prefer to see m (metres) rather than km, it is my opinion that it is safer and more accurate, but it is certainly my preference.
  • Using km does however allow the m (miles) -> mi step to be skipped completely.
• Gradually metricate all other distance signs, including route confirmation and other signs. to an accuracy of 90%.
  
  • For route confirmation signs, distances less than 1 km should be rounded to the nearest 0.1 km.
  • Distances from 1 km to 10 km (inclusive) should be rounded to the nearest 0.5 km.
  • Distances 10 km or greater should be rounded to the nearest 1 km.
• Replace all imperial-only restriction signs with metric-only signs.  Dual-unit signs can be replaced with metric-only signs either as part of this changeover, or as part of post-metrication maintenance.
• Configure (or if required replace) 2-digit variable speed limit signs to make them capable of displaying speed limits of 100 km/h or more.
• This is a good time to consider removing clutter, and making signs more symbolic.  Both should be included where they relate to metrication.
• I strongly suggest modifying the graphics for lane restrictions as shown in this previous article in particular, and several other articles (especially the roadworks articles).  It makes lane restrictions clearer.
• The signage improvements I have suggested can either be included or deferred as post-metrication work

Why metres instead of kilometres on certain distance signs?

I have been asked as to why I suggest metres and why not kilometres and decimal fractions of a kilometres, on certain exit signs (specifically motorway exit signs and service signs) and on supplementary plates.  So that 1 mile is replaced by 1600m and so on. For the record, I do not oppose using km on motorway (and other) exit signs and service signs in principle, as long as the correct symbol is used (km).  But the concern I have is that if decimal points are used e.g. in 1.6 km, then there is a risk of someone missing the decimal point when glancing at the sign while driving at speed, thus the distance of 1.6 km could be confused for 16 km (even when the 6 is made smaller than 1).

I do not oppose km on motorway exit signs in principle, and if it can be proven that 1.6 km, 0.8 km, can be read safely at a distance and at speed and not cause anyone to misread 1.6 km as 16 km or 0.8 km as 08 km, then I would not have a problem with it.  I have not heard of this being done in any country with wholly metric road signs, which is almost the entire world - either whole numbers of km or whole numbers of m are used.  I have not heard of anyone converting or planning to convert (in continental Europe), say 1500 m to 1.5 km.  Note however, that the use of vulgar fractions (¹⁄₄, ¹⁄₃, ¹⁄₂, ²⁄₃, ³⁄₄, etc.) is not recommended, as this is not standard under SI, standards should be respected.

But sticking only to metres avoids this issue in the above paragraph.  Yes, it means 1 or 2 extra characters for distances of 1000 m or greater, up to 3000 m but I don't see this as a problem, and a four digit number followed by a symbol with one letter does not constitute clutter.  Plus if people are familiar with 1500 m races, I say why not have 1500 m on road signs too.  And as already explained in my other article, it also gives more flexibility in terms of signage placement or conversion, the 90% accuracy rate is maintained, and there is no problem reading this at a glance.  I don't see an extra 1 or 2 extra digits as a problem as clutter.

For using metres though signs I would recommend that the signs be rounded to the nearest 100m and only use multiples of 100m where possible, so use 500m, 1000m, 1200m, 2000m etc.  However I do agree that 1250m, 2750m for example should be avoided, as it is best to keep the numbers simple.

Speed limit changeover - preparation and the changeover

In the previous articles, "Speed limit signs", and the related article "Improvements for UK speed related signs", example signage has already been shown.  The focus of this subsection is on the preparation and changeover processes.

For speed limit signs, the changeover ideally has to be overnight for obvious reasons, but can be spread over a long weekend.  What can also be considered is to having England, Scotland, Wales, and Northern Ireland work to different timetables, with Northern Ireland first to finish going metric. The UKMA has suggested within 3 years of the metric road signs announcement, so that the changeover would happen at the middle of the 5 year changeover for all of the UK.

That said, in principle the speed limit changeover can also happen at the beginning (as in Canada) or at the end (as in Australia and Ireland).  For me I am not bothered when it happens as long as it happens, and above all as long as it is done properly.  If it is done properly, quickly, swiftly, and above all with a short sharp campaign of publicity beforehand, then the public will adapt quickly, just like members of the public in Australia, Canada, New Zealand, South Africa, India, Ireland, and so many other countries that finished their changeover to metric speed limits.  There is no reason why the UK should be any different.

The speed limits would need to be reviewed, to see whether they are appropriate for the area. There would be more choices available for those making decisions on speed limits, but they should take into account whatever the conditions are - so near an accident blackspot, where there are a lot of pedestrians, or (especially) near a school, it would make sense to reduce the speed limit, if necessary even lower than the converted speed limit.

But by default, the posted speed limit changes are expected to be converted as follows:

Speed limit before (imperial)	Speed limit before (equivalent metric)	Speed limit after (metric)
5 mph	8 km/h	5 km/h
10 mph	16 km/h	10 km/h
15 mph	24 km/h	20 km/h
20 mph	32 km/h	30 km/h
25 mph	40 km/h	40 km/h
30 mph	48 km/h	50 km/h
40 mph	64 km/h	60 km/h or 70 km/h
50 mph	80 km/h	80 km/h
60 mph	96 km/h	90 km/h or 100 km/h
70 mph	112 km/h	110 km/h or 120 km/h

Note that I have included all possible cases, speed limits of 20 km/h or lower would be expected to be found on private roads.

Examples of a minimum and maximum speed limit conversion is shown below:

Examples of conversion of minimum and maximum speed limit signs from on changeover day, with subtitles removed gradually after metrication.

Post-metrication changes are also shown in the diagram above, the gradual removal of the km/h subtitle after the changeover day, but this is described in more detailed in the next subsection within this article, "Post-metrication changes".

Some might worry that a 2 km/h (slightly more than 1 mph) speed limit increase for urban areas will be unsafe, but one has to remember that in the UK, speedometers are required to have a tolerance of 10% + 2 mph (i.e. up to 35 mph).  50km/h would fall within the tolerance of the old speed limit.  Plus 50 km/h is the default for urban areas in the vast majority of countries, including Germany which in particular has a very good road safety record.  There are other factors besides speed when considering road safety as well. Nonetheless, it is worth also considering introducing 40 km/h speed limits or 40 km/h Zones (as I would recommend) where safety can benefit.

Rural roads have a high accident rate, so it is worth considering reducing the default speed limit there.  For cars and motorcycles on rural roads, one can have a speed limit of 80 km/h as in Ireland, 90 km/h as in France, or one can increase the limit instead and have the default speed limit set to 100 km/h as in Germany.  Similar adjustments would need to be made for other vehicles as well as cars.  But it would also make sense to review the roads and see which speed limits are more appropriate (and where necessary introduce lower posted speed limits).  Metric speed limits gives more limits to choose from and the limits can be tailored better to local conditions.

For the default motorway speed limits for cars, given that the existing limit is 70 mph (112 km/h), the limit can be reduced to 110 km/h, or increased to 120 km/h. An increase in the speed limit would be popular, and 120 km/h falls within the 10% + 2 mph tolerance for the current speed limit in the UK.

Other possibilities include raising only the motorway limit to 130 km/h (for which the motorway would need to be better maintained) which would be popular especially with motoring groups, but that environmental groups would be unhappy with. Another is to reduce both motorway and dual carriageway limits to 100 km/h which environmental groups would laud but motoring groups would be very unhappy with.

The dual carriageway limit, whether or not expressways or expressroads (Kraftfahrstraßen / Voies rapides) are introduced will also need to be considered. Expressways should have identical limits to dual carriageways for all vehicles to avoid confusion if they are introduced in this changeover.

Vehicle speed limits should be brought in line with speed limiters where applicable. This is easy to do and does not require signage. However, the limits for other vehicles need to be defined in terms of metric.

One example I have come up with for default speed limits, based on existing rules, is as shown below (and using road sign graphics):

Default speed limit per vehicle class, this is an example.  Note that there are currently no roads classed as Expressways (Kraftfahrstraße / Voies rapides) in the UK.

Lorries and buses, which already have primarily metric speedometers (and secondary imperial) and metric odometers, will need metric-only stickers which state the speed limiter settings.  This could be required today with no consequences, as motorists in the UK will already  Examples are shown below:

Speed stickers for various classes of vehicle.

Notice how km/h subtitles were included.  But given that there are already lorries from continental Europe with these stickers on the back without the subtitle, saying "90" or "80", it obviously cannot be mph, it is km/h.  Even though this could be deferred until after the changeover, I personally don't see any safety issues in having speed stickers without the km/h subtitle on the day of the changeover, or even before, but that is just my opinion.

Speed stickers for various classes of vehicle.  No km/h subtitle was included.

And that is to prepare for the changeover. As well as this, the new speed limit signs can either be manufactured in advance for the changeover (which would look better), or adhesive stick-ons (which would be cheaper).

There is the question about what to do about variable speed limit signs. The UKMA has expressed concern that the DfT is not planning for the future, by installing variable speed limit signs only capable of displaying 2 digits. Readers on this blog said they would be surprised if this was true. Either way I hope that it can be reconfigured to support 3 digits, otherwise these would have to be (physically) replaced. Either way, variable speed limit signs do need to support 3 digits, the first digit would always be a 1 in three-digit speed limits however.

In the final months leading up to the speed limit changeover, there would need to be a short, sharp campaign of publicity, using all available media, with posters and adverts used as necessary. The public must have it made clear that speed limits will be metric. Even though speedometers are required to be dual unit in the UK, there is concern that in some cars with analogue speedometers, the metric-part is unreadable. So it is worth making sure that everyone has a conversion chart ready for the changeover (as well as what the new default speed limits for different classes of road), as part of the general publicity.

Metric speed limits and their imperial equivalents.  This can be printed and used.

During the day of the changeover, one idea could be to turn off speed cameras as an incentive for motorists.  And gradually reconfigure speed cameras to use metric, or turn them off for a limited time period, reconfigure to metric, then turn them back on.  Alternatively speed cameras can be reconfigured (or replaced if required) to use metric signs on the day of the changeover.  However, I believe that speed cameras should only be used in areas where there is a genuine need to do so, like on accident blackspots, not as a revenue generating machine, so metrication would be a good time to see which speed cameras are actually needed, but that is another issue for another article, and has almost nothing to do with metrication.  Furthermore, the public will already be clear that the speed limits will be metric due to the changeover publicity beforehand.

Other consequences of the changeover are quite minor, the highway code will be revised (including graphics and measurements), along with the relevant literature (for example the traffic signs manual), anyone in the car, motorcycle, or van industries will have to start recording distances in km from changeover day rather than miles, distance travelled for expenses reports etc will also be in km rather than miles, however one can convert from miles to km if the distances are given in miles for older cars - this is only what British and American car owners have to do if they bring their cars abroad to anywhere else in the world if they move (except the UK or USA among the major countries).  As mentioned earlier, UK-registered buses and lorries  already have odometers and tachymeters in km, as well as primarily-metric speedometers, and km based speed limiters, and taxis have km based tachymeters too.

Post-metrication changes

As a post metrication task, it is worth removing the km/h subtitle. It is useful as a reminder once the speed limit changeover has been completed that the speed limits are now in km/h, as was done in Ireland. However, after the changeover it becomes clutter, and can be phased out. New signs with just the number in a red circle can replace the signs with subtitle gradually.

The signage improvements below can be done as a separate post-metrication task too, where applicable, as described in the subsection "Signage improvements" below.

Signage improvements

As for my thoughts in the "signage improvements" and signage suggestions, I believe that they are best done as a post metrication task if cost is an issue, or it can be incorporated into metrication (but I believe this would increase the budgetary requirements). Or they can be done today where they have nothing to do with metrication. But I would recommend incorporating the signage improvements as they are intended to make signs easier to read at a glance, and reduce clutter.  Indeed, as well as being fully metric, British signs should also respect international standards (and agreements), be fully compliant with and implement fully the Vienna Convention on Road Signs and Signals, use graphics rather than text where applicable (even on supplementary plates), and clutter should be removed where it exists.

You will have noticed that many of my designs are based on examples from continental Europe, especially Germany, as I believe these have examples of good practice that can be incorporated into British signage where applicable.  Signs from continental Europe tend to be symbolic and easy to understand (even if you know zero of the spoken language you can still drive there without problems). British signs in general mostly follow this principle too as a result of the work done by the Worboys committee which is very good indeed (a shame that metrication wasn't included within their remit as well), but there is still room for improvement and clutter removal - these have been identified in my articles, and I have looked at signs from continental Europe, especially Germany, as examples of good practice for clutter free wholly symbolic signs.

Planning on sending my thoughts

I am planning on sending my thoughts to the DfT, on metrication, 24 hour time, and my thoughts on possible signage improvements (in the form of a PDF document), and either responding to consultations or mailing the DfT directly. If anyone wishes to add anything, or would like to add anything, please feel free to let me know and I will include your suggestions that I agree with or see the benefits of.  At the time of writing, I am planning on sending my thoughts to the DfT at some stage in the future.  I also plan on mentioning this in a future consultation on road signs as well, although I am not sure if it will be possible given that I live permanently in France.

The more controversial designs I have decided to reject myself - the relevant articles have already been updated.

Acknowledgements

And finally I would like to thank all those who read and commented on my articles on metrication and signage improvements, and in particular Kevin Steinhardt, Bryn Buck, Alexander, Andrew, Hughster, Gareth Parr, Tahrey, Mark, SwanseaSteve, WJG, Simon Patterson, all the anonymous commenters, the SABRE members not already mentioned, and everyone else not already mentioned, for taking the time to read my articles and review my designs. Your feedback, praise, and constructive criticisms were most invaluable. I have tried to take into account your suggestions where possible when making updates to my articles. Once I have sent my thoughts, we will see how the DfT responds.