When the latest Traffic Signs Regulations and General Directions (TSRGD) came into force in April 2016, imperial-only restriction signs for height, width and length were no longer authorised. However, the Traffic Signs Manual (TSM) that provides guidance to road contractors on signage has not been updated since 2009 and still includes imperial-only restriction signs to this day. Six months ago, I asked my local MP to contact the Secretary of State for Transport to ask why the Department for Transport has been promoting the use of unauthorised imperial-only road signs since 2016. I received a reply from the DfT a few days ago.
This is the email I sent to my local MP Sarah Sackman on 19 December 2024:
“Dear Sarah Sackman MP
On page 98 Chapter 8 Part 1 of the Traffic Signs Manual (TSM), there are diagrams for both imperial-only width and imperial-only height restriction signs for use in road works and temporary situations – signs which have not been authorised for new sign installations since the Traffic Signs Regulations General Directions (TSRGD) 2016 came into force in April 2016.
The TSM has been promoting the illegal use of imperial-only vehicle restriction signs since 2016.
The diagram for weight restriction signs is also obsolete as it includes the now unauthorised upper case “T” symbol to represent tonne. The diagram for this sign was corrected to show the lower case “t” in the 2011 amendment to the TSRGD.
Can you please ask the Secretary of State for Transport why the Department for Transport has been promoting the use of unauthorised imperial-only road signs and unauthorised weight restriction signs for the last eight years.
Here is the link to TSRGD 2016:
https://www.legislation.gov.uk/uksi/2016/362/pdfs/uksi_20160362_en.pdf
Here is the link to Chapter 8 Part 1 of the Department for Transport’s TSM:
https://assets.publishing.service.gov.uk/media/5a74adeaed915d7ab83b5ab2/traffic-signs-manual-chapter-08-part-01.pdf
Ronnie Cohen”
On 4 February 2025, I got an email telling me that Sarah Sackman has written to the Department for Transport on my behalf.
On 10 July 2025, Sarah Sackman received the following reply from the DfT, which she forwarded to me:
Why wasn’t the TSM updated at the same time as the TSRGD? Why is it taking the DfT so long to update the TSM to bring its guidance into line with the current road sign regulations? For the last 9 years, the TSM has endorsed and promoted the use of unauthorised (i.e. illegal) width and height restriction signs. I got no explanation for the long delay to update the TSM and why the discrepancy between the TSM and TSRGD has been allowed to persist for so long. It is a symptom of the continuing measurement mess as the UK struggles to move forward on metrication. It does the government no credit at all.
For more information about this issue, see https://metricviews.uk/2024/12/05/does-the-traffic-signs-manual-promote-the-illegal-use-of-imperial-only-vehicle-restriction-signs/.
Metric Views 
I wonder if Chapter 8 of the TSM would be “currently in the process of being updated” if you hadn’t written to them first.
Let’s hope it doesn’t take too long for the update to be published.
LikeLiked by 1 person
It would be interesting to know how many unauthorised imperial-only signs have been put up since April 2016. Is it possible to find out? Would there be any centralised records of erected signage, legal or otherwise? What a great image of Britain in the 21st century!
LikeLike
@metricnow since rekindling my love of motorbikes a couple of years ago I’ve spent a lot of time out on a lot of different roads and have been shocked by the number or seemingly new imperial-only signs where there should be dual signs, they appear to be predominantly on country lanes, usually for railway bridges and fords. In my general area both Bedfordshire and Milton Keynes seem to be particularly bad (Northamptonshire has been quite good but I know of at least one dual width sign that was replaced with imperial only just before the rule change).
I’ve also given up on complaining about signs around Wansford in Cambridgeshire (predominantly on the A47) that have been replaced since my initial complaint and still show two weight limits in the village, one in tonnes but the other in tons. It appears that even though the time limit in savings regulations has long expired they have no desire to make it legal.
I can’t see any of the Reform-run councils being pro-active on this issue.
I was pleasantly surprised at the weekend to see a maximum vehicle length sign in metres only with no imperial equivalent though as it’s likely not legal I’m not going to say where I saw it!
There really should be a legal requirement for authorities to have a detailed record of all road signs but would not be surprised if there isn’t. In this day and age there should be no excuse for not having a database used for maintenance purposes.
LikeLike
The Traffic Signs Manual is a large document of several volumes. It would be unrealistic to expect the Manual to be updated every time there is a change in legislation of some specific issue.
I can give a parallel case here. In 1970 I was working as an electrical maintenance supervisor in a small power station. This was a pivotal year for electrical wiring and installations. One big change was new standards of cabling, for both permanent installations and portable appliances. New metric standards were replacing the imperial ones, and also the colour coding for the insulation for flexible cords was changing.
To address this, a supplement to the IEE Wiring Regulations was published, to state the new cable standards and additionally to specify the application of the regulations in metric terms. Every imperial measurement in the existing regulations was given a metric equivalent. This covered aspects like minimum height to install a power socket above a surface, minimum depth to bury a steel-armoured cable, etc. The whole IEE regulations were updated some years later, using metric units throughout.
I procured metric-only folding rulers for my team, encouraged them to use them and said that my job specifications would start to use metric measurements. The idea of working with metric measurements was generally accepted by the team, though there was some dissent over the general design of the new metric standard twin-and-earth sheathed cabling.
In the case of traffic sign regulations, I would have thought that following the updated regulation for height and width signs, there would have been a supplement issued with these directions. At any rate, it would have been pleasant for the Minister to say so.
Meanwhile, round here in Hampshire I see plenty of dual-standard height and width signs, and I even know of a metric-only one on a low bridge. (Probably illegal but I won’t tell.) We have just returned from a round-England staycation, taking in the midlands, north-east and north-west. Again, the majority of such signs seem now to be dual-standard. The occasional imperial-only ones are now beginning to stand out as oddities. I can’t speak for Bedfordshire and Buckinghamshire, as Free Thinker relates – perhaps some county councils are less prescriptive about applying regulations than others. Neither am I sure whether temporary signs, as used at road works, are slower in moving to the new standard.
At any rate, eight years after the new regulation, the job seems to be progressing well. I don’t think we have too much to worry about.
LikeLike
Ideally an new updated standard would specify metric only signs and local authorities would adhere to it.
Ezra aka punditgi
LikeLike
punditgi wrote: “Ideally an new updated standard would specify metric only signs”
Indeed, local authorities have had the option for dual units since 1981. That’s 44 years already.
LikeLike