New insights into DfT thinking in recent years

In this article, Ronnie Cohen passes on information he has recently received from the Department for Transport (DfT).

In April 2017, I received a response to an FOI request that included a document called “170411-Annex A”. This document contains internal DfT correspondence that reveals a lot about DfT thinking on the use of measurement units on vehicle dimension signs.

Some material in Annex A of the DfT reply to my FOI request can be found at This will not be repeated here.

There was some correspondence about Phillip Hammond’s decision not to phase out imperial-only vehicle dimension signs in 2010 and noting someone’s expressed interest in the imperial units appearing above the metric units on dual-unit vehicle dimension signs.

Reasons for use of Dual Unit Signs

In response to concerns about the cost of placing two signs at each site, the DfT designed a single dual unit sign as an alternative to the existing two prescribed traffic signs. This design would reduce traffic sign clutter and the installation and maintenance costs for local authorities who chose to provide dual unit signing.

For this reason, the Transport Signs Policy Branch asked for an improved design for the discretionary “headroom” warning sign incorporating both imperial and metric units to be included in the Transport Signs, Regulations and General Directions (TSRGD).

Why Metric appears above Imperial on Dual Unit Signs

Here are a few quotes to explain why dual-unit width and height limit signs show the metric units above the imperial units:

“Our earlier advice did not explain that although the proposed dual-unit triangular warning sign is an entirely new sign, there is an existing dual-unit circular regulatory sign, which has been prescribed and widely used around the country since 1994. When the existing sign was designed, a conscious decision was made to place the imperial below the metric legend. The reasons for the decision were purely based on efficient use of sign space to minimise the overall size of the sign whilst maximising legibility, particularly at night. If you look at the sign in Annex A you will see the imperial legend is widest at the top (because of the inches notation) and the metric text is widest at the bottom. The widest parts of each legend were therefore located together in the centre i.e. the widest part of the sign.”

“When designing the new triangular warning sign, it was desirable to place the widest part of the combined legends as low down as possible, where there was greater width. Placing the imperial legend above the metric would require a step up in the standard size of triangular sign to accommodate the size of font and spacing between the legend and the border required for clear legibility. Larger signs mean greater implementation and maintenance costs for local authorities. They can also be more difficult to locate on bridge structures or be unnecessarily visually intrusive in terms of street clutter.”

“A decision to place the imperial legend above the metric would result in larger signs and some inconsistency issues.

Concerns about misunderstood Imperial Units

There was concern about a lack of foreign drivers’ understanding of imperial units: “Bridge strikes continue to cause significant disruptions to the road and rail network and these strikes could cause a potentially major incident. Chapter 4 of the Department’s Traffic Signs Manual recommends that metric heights be shown on roads used frequently by foreign drivers because they are involved in a disproportionate number of the bridge strikes.” What follows are details of prescribed vehicle dimension signs in the TSRGD at the time.

DfT Reaction to Metric Views Articles

Robin Paice’s comment on the “Who should pay for metrication of road signs?” Metric Views article, was forwarded by a DfT civil servant to others on 5 December 2011, whose names were all redacted, with the following remarks:

“The story continues …. Sad to say, I enjoyed the article and the comments to it. Good background stuff for correspondence on this.”

Robin Paice’s email about the “Metric signs on UK roads: your FAQs” Metric Views article, was forwarded by a DfT civil servant to others on 30 January 2012, whose names were all redacted except for one Anthony Boucher, with the following remarks:

“Fyi – well constructed, if fatally flawed. Given the costings we have been provided for signing 80 mphs [sic], the estimate for conversion must now greatly exceed our previous estimates.”

Shift in DfT Policy on Use of Metric

On 10 June 2014, Robert Goodwill MP, the then Parliamentary Under Secretary of State for Transport, emailed Submissions (cc Steve Gooding, John Parkinson, Anthony Boucher), in response to submissions about updated guidance on the prevention of bridge strikes, saying:

“Hi [name redacted],

Many thanks for your submission.

As we discussed today, the feels [sic] it would be beneficial to mandate dual unit signing – firstly for then new generation of young drivers who learn metric in school, and secondly, foreign drivers who may understand metric only.

He is happy for the report to be published however would appreciate if we could look at the above during the TSRGD review.”

An email to Robert Goodwill MP on 14 October 2014 suggests the removal of imperial-only vehicle height or width limits in the next version of TSRGD and that the revised TSRGD no longer prescribes imperial-only signs, so that in future when signs are replaced they must be dual imperial and metric signs. The transport minister Patrick McLoughlin agreed with the recommendations. It took a few days for the government to accept this idea. A previous transport minister Phillip Hammond rejected it a few years ago.

Options for Removal of Imperial-Only Vehicle Dimension Signs

Two options were considered for removing imperial-only vehicle dimension signs:

  1. Allow imperial only signs to remain in place only until such time that they become life-expired, or replaced during routine maintenance, at which time the dual-unit equivalent must be used.
  2. The alternative option would be to mandate in TSRGD that only dual-unit signs could be used.

Option 2 was rejected because “it would impose an unfunded burden on local government that would need to be found from DfT budgets, and would force local authorities to replace signs in preference to other planned maintenance work.”. The DfT estimated this cost to be £2 million in 2015-16. The DfT added that “As the removal of imperial-only signs was not included in our recent consultation on TSRGD, there is a risk of that the policy could be challenged by local authorities.”.

The DfT went for option 1 because it is cost-neutral. The DfT said that “We recommend a cost-neutral option that removes the prescribed signs from TSRGD when it is amended. This will allow imperial only signs to remain in place only until such time that they become life-expired, or replaced during routine maintenance, at which time the dual-unit equivalent must be used. This disadvantage of this approach is that it will take time to see the removal of all imperial only signs, but local authorities already have the freedom to replace any signs, and could do so if they have concerns about potential bridge strikes. This option would deliver the policy change, be cost-neutral, and retains the freedom for local authorities to act at greater pace if they have any concerns over any of their existing signs.”

Fear of Media Reaction to Metric Adoption

Another factor that motivated the DfT to go for Option 1 is fear of the hostile reaction of the popular media. On this issue, the DfT said, “While it is expected that any decision to withdraw imperial signs would be welcomed by road users, the loss of imperial-only signs might be viewed by some stakeholders and media as further evidence of the loss of ‘British’ systems. Imposing dual signs on local authorities is unlikely to be well received, with the possibility of negative comments being played out in the media.”. One email with the subject heading of “TSRGD Stakeholder Engagement” reveals that “The change generated some national press interest with articles from the Daily Telegraph and the Daily Mail, both saying that it could lead to further metrification [sic].”

Another quote on this issue stated, “There is a small risk that media could pick up on the fact that we are still allowing the dual unit sign to be used. However, press office will have lines to take explaining that we are giving councils the option of using a dual unit sign or a sign with imperial measurements.”.

That provides an indication of how much our political leaders fear the mass media and do not dare to challenge this mindset. Hence, it is so rare to find any who are willing to make the case for completing the UK’s transition to the metric system.

11 thoughts on “New insights into DfT thinking in recent years”

  1. ““Fyi – well constructed, if fatally flawed. Given the costings we have been provided for signing 80 mphs [sic], the estimate for conversion must now greatly exceed our previous estimates.”

    It would be nice if the UKMA could request to see their cost estimates and how they derived them. I’m sure the cost estimates have been deliberately exaggerated. Having an independent review of the estimation of costs may prove positive in bringing to light less expensive methods to achieve the same goal, such as the use of adhesive overlays.

    In the next section on imperial only sign removal, a method not mentioned would actually be more cost effective. That is covering the imperial with a label indicating the dual value. This could be done nationwide in a days, rather than years or decades. Then when the sign actually needs replacement, the replacement would be new one.

    “The DfT estimated this cost to be £2 million in 2015-16.”

    An overlay label would not cost this much. Why wasn’t this method suggested?

    I’m surprised that there is no mention of amending the law to allow for metric only signs. No changes to the signs need be made simply by allowing metric only or metric primary. But it would have the effect of making the removal or damaging of such signs illegal and punishable. This simple step must be taken to safeguard metric only signs that many progressive communities have erected and may wish to erect in the future.

    How many metric only signs would exist now if the law had simply allowed it?


  2. Just lifting the ban on metric units on signs would go a long way to clearing this mess up and would give certain groups no basis for their action which, regardless of the status of the signs, is nothing more than vandalism.

    Sure there is a little scope for confusion, the main one being where signs have been allowed to use “m” to mean mile (which was even mentioned in a DfT document decades ago!) but most drivers are intelligent enough to understand the context so the use of “m” to replace yards could be made optional immediately with little or no impact while a plan could be put into place to gradually remove instances of “m” for miles (plate over with a blank or “mi” alternative) and a leaflet sent out with road tax renewal notices to educate drivers.

    It’s absolutely bonkers that we seem to be the only place that actually bans metric signs when even the USA allows them!


  3. @Daniel:

    When Canada converted using reflective adhesive overlays, the cost in CDN at the time was $26 per speed limit sign (distance and width/height signs took much longer, often as routine sign replacement). Today, that amounts to around £55 per sign, using escalation data since 1977 and at current exchange of C£1.73/£1.00.


  4. If changing the road signs to metric is out of the question, what about considering the practicability of dual distance and speed limit on the main roads from the cross channel ferry terminals to London? This would help prepare outbound traffic for the metric signs on the Continent and to educate inbound foreign drivers for signs in imperial measures.

    As a first step, this could be tried out on the main road from Dover to London.

    What do others think?


  5. @Michael Glass

    I think dual speed limit signs would be a major problem. If two systems of measure are used, units must be CLEARLY marked. The UK presently uses a roundel design with no units. A new design would be required that allowed for two numerical entries of the same height as present (vs speed of road) plus room for units. The diameter would nearly double. Perhaps near the border, units should be shown within the roundel, and a special warning sign reminding drivers of a unit change ahead. This would also be an issue for Ireland and Northern Ireland which have a land border.

    Further, for most speeds, it would not be possible to round both numbers. The US has set designs for speed limits in either MPH or km/h, but the MPH limit must be a multiple of 5 MPH, and a metric limit a multiple of 10 km/h. A handful of values exist (eg 25 MPH, 40 km/h) where the rounding accuracy is acceptable. Would 30 MPH be shown as 48 km/h or 50 km/h? Is going the faster of the two limits (assuming the driver can determine that) acceptable? The US has no acceptable design (MUTCD) for a dual-measure speed limit sign, it is either/or; however, some cities have made them up but they are much larger than a normal sign and I think they add more confusion than clarity. (Note that metrication has stalled out in the US, and there is no case where a metric speed limit is the true and enforced speed limit; any such signs are “info only.”)

    Dual distance is a problem because the UK insists on misusing “m” as the abbreviation for miles. A sign displaying 5 m | 8 km would look truly bizarre. I suppose if “mi” could be used as in the US, that 5 mi | 8 km would work.


  6. John,

    What does it cost to completely replace a sign in the UK compared to the price of an overlay?


  7. @John Steele legislation allows speedometers on European cars to mis-read by anything up to 10% (under but not over) and my experience is that most manufacturers err on the side of caution, my most recent vehicles seem to have been going anywhere as slow as 64 mph when the speedometer actually read 70 (a good GPS unit is, despite what we’re officially told, is actually very accurate these days and the plethora of digital signs warning us to slow down by showing our actual speed also bolster that evidence).

    Additionally, some authorities have had a lot of flack from some motoring organisations (some, in my opinion, actually justified) for lowering speed limits to levels that are are actually too slow for the conditions and hence ignored by a large number of drivers.

    Based on this I don’t think that rounding speed limits in km/h to the nearest 10 from their current mph equivalent would probably have a great deal of effect on speeds on most roads anyway.

    I do often wonder if dual speed limit signs for a period, providing they were properly marked AND there was a proper driver education campaign prior to it happening, would actually be as much of a problem as some people might think.


  8. There are a number of problems with dual speed limits:

    1. In law, which would be the true speed limit and which the approximation?

    2. The actual lettering on a dual unit speed limit would be much smaller than the current lettering and this could be counter-productive in respect of road safety.

    3. Having dual speed limits would hinder the conversion to km/h unless there was an absolute ban on mph being displayed on speedometers fitted to new cars.


  9. The signs that really get to me are the ones warning of, for instance, a two metre width restriction eighty yards ahead.


  10. @Michael Glass:

    A complete switch to metric is not ‘out of the question’, no matter how much imperial fans (within and without DFT) would prefer us to believe it is. I’m personally against dual units altogether and not persuaded by limiting it to port roads or even prioritising particular classes of road. In theory, the dual unit width signs were supposed to be rolled out first to temporary motorway lane restrictions for the benefit of foreign HGVs. In practice, the Highways Agency is the most hidebound and ornery authority who are still rolling out imperial-only signs on new roadworks which most HGVs routinely ignore.

    @Daniel Jackson:

    It’s more difficult to correctly position the overlay vertically at 2.3 m above ground even on a windless day, backed as they are by fussy adhesive that effectively gives you only one chance to avoid a wrinkled embarrassment. Plus, you’d likely have to give most old signs a thorough cleaning and drying (and remove any anti-graffiti covering) for it to be tenacious. Also not in Winter outdoor temperatures. For many decades, all road signs in UK have used stainless steel [metric] fasteners precisely to make them easy to take down for maintenance, or for ARM to thieve. Once the decision is taken to convert, it will possibly be logistically simpler and cheaper to swap standard signs, including distance subplates, in one visit and reuse or recycle the substrate to make up subsequent batches. Some large rectangular signs—advance direction, route confirmation, etc.—comprise of standard sized modular panels which can similarly be swapped (WARNING: may contain soft metrication). Those which don’t could be amended (hopefully at the proper text size) and returned to their original position in two visits with a temporary absence of the sign—not a significant problem. As John Frewen-Lord hints, this is already done continuously for all signs when they become life-expired, unaccompanied by hysterical tabloid headlines or exaggerations about the supposedly intolerable cost.

    DFT cost ‘estimates’, as they were with the height and width signs, are probably based on a worst-case scenario (road closures, diversions, cranes, overtime, etc.) for the most inaccessible sign in the kingdom and then just multiplied by the total number of signs. I’m actually quite impressed that they now know how many signs have imperial measurements on them 😮. If they took into account economies of scale and the fact that the vast majority would be trivial to do, the overall figure might start to look less objectionable—the very last thing they want!


  11. @John Steele:

    Modern-ish UK railways use black numbers on a white background for imperial speed limits and white numbers on a black background for metric—both in a red roundel—without explicit unit marking. Also differential speed limits depending on rolling stock type/ tilting and advanced warning signs; braking trains is a relatively protracted affair. But all drivers are tested and certified for knowledge of their route’s speed limits as though the signs were missing or obscured. Even then, dual limits are considered a bad idea! Trams running on UK streets use black numbers on a white background in diamond-shaped signs and always metric—also without explicit unit marking. The part of the Tyne & Wear Metro with hexagon-shaped signs is the exception that proves the rule 😉.

    @Martin Vlietstra:

    1. Given the pre­existing levels of motoring lawlessness and official blind-eye-turning to that, it’s hardly a critical issue. TPTB are not even slightly bothered about the level of danger imposed either way.

    2. The lettering on imperial-only motor speed prohibition signs is already excessively large—fully twice the size (i.e. four times the area) of that on corresponding height/ width/ weight signs, imperial-only or dual. Something would have to give for a leading ‘1’ to be added in a straightforward switch to metric-only anyway, either smaller numbers or use of Motorway typeface of the same numeral height. Alternatively, jump straight over km/h to m/s!

    3. All dual unit signs are a terrible idea for this reason. Same arguments apply to height and width prohibitions, where UKMA were/ are in favour.


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