New speed limit in central London

Ronnie Cohen, one of our regular contributors, comments on the introduction on 2 March of a 20mph speed limit on certain roads in London’s Congestion Charging Zone.

In the Metro newspaper published on Monday 2 March 2020 (Travel News section, page 39), Transport for London (TfL) announced a new 20mph speed limit had been be introduced on the roads it manages in the Congestion Charging zone. The article gave all speeds in miles per hour and all distances in kilometres. Apparently, TfL like many other organisations in the UK sees nothing unusual with mixing two measurement systems in the same article.

The new speed limit involves new signage, road markings, raised pedestrian crossings and re-calibrated speed cameras, publicity and advertising, a new speed enforcement team, new laser video technology and TfL co-operation with boroughs and the public. It is being rolled out across 8.9 km of roads in the Congestion Charging zone. Over the next five years, TfL is planning to introduce safer speed limits across another 140 km of London’s roads.

These measures are intended to make our roads safer and are part of the TfL Vision Zero commitment to eliminate deaths and serious injuries from London’s roads by 2041. Safety measures are to be welcomed. But the introduction of 20mph signs and road markings in recent years is surely a missed opportunity to introduce metric signs. If they had been metric, they would have cost no more than the current imperial versions.

Information on costs and funding did not feature prominently in the news about the CCZ 20mph limit (in contrast to the successive proposals for the conversion of the UK’s road traffic signs to metric measures). The question of whether there would be be extra funding for new signage, etc, or diversion of funds from other parts of the transport budget was left open, but there appeared to be an implicit assumption that the money would be there.

Covid-19 had not made an appearance at the time these plans were being prepared, and the economic consequences of the pandemic could not have been foreseen. We must hope TfL Vision Zero does not take as long to be implemented as the proposals for metric road signs – 50 years and counting!

As well as the printed Metro article, you can find the same story on line at the following links:


25 thoughts on “New speed limit in central London”

  1. We can now at least state with more certainty that road miles shown in km is a de-facto occurrence.
    This further advances my theory stated elsewhere on these pages that UK now has a de-facto “UKC” (UK Customary) measuring system which will be with us for the rest of our lives.


  2. Daniel, 8.9 km, speculation, but probably because that will be a precision survey measure, not a random estimate.
    Given the value of land in any big city, let alone London, I would guess they know pretty much the road lengths to the millimetre!
    We do have a pretty good metric surveying record in this country, OS is pretty much all metric in its survey work, annoyingly though, not in its leisure book publications which stop me from buying them.


  3. Why is our Highway Code book nearly all metric when we have medieval distances and speed limits shown on our road signs.
    Mixing up different units of measurement on the highway or in the official Highway Code book and the media does nothing for road safety, it confuses our children and is one reason why our driving test is tricky to pass.
    I stopped being a fossilised Luddite many decades ago and my life has a whole new meaning!


  4. I wrote to the UK Department for Transport a few years ago asking why they didn’t do something about changing road traffic signage to SI units and they replied that it was solely due to cost. Why is cost not a problem where imperial signs are concerned?


  5. @Cliff, cost is costing.

    I guess the D[a]fT know quite well this cost mantra is just a red herring. Their estimates of converting road signs have been trashed any number of times, it makes no difference to them.
    The cost of official duplicity (in all spheres of UK life) and all it involves must be staggering.
    Given the mixed-muddle errors I alone make as a fully imperial-conversant SI convert makes me wonder how others cope, although I do at least have age as an excuse.
    It is our money they are wasting and us they are hurting. The 18th century UK beckons.


  6. Cliff:

    So the Department for Transport did not reply to you that there was an objection on ideological or any other grounds, and that the problem of conversion was solely one of costs. Well, we know that argument was debunked by UKMA quite a few years ago: distance signs can be replaced over a period of time, overlays can be used, costs can be spread over different budgeting periods, etc. The only thing that needs an ‘M’ day is the conversion of speed signs to kilometres per hour, but there are excellent precedents in countries like Ireland, Canada and Australia. We seem to be in a stalemate situation: the DfT claims it cannot do it on the grounds of cost, we say it can and have even produced publications setting out how it can be done. It’s amazing how quickly the Government can find whole forests of magic money trees when it so wishes, as we are witnessing at the present time when thousands upon thousands of people and businesses are being financially supported during the pandemic, yet cost is cited as the excuse for not implementing an eminently sensible and pragmatic conversion of road signs to the units of measurement taught in schools, SI units, in normal times. What do people in other countries make of this, I wonder?


  7. @Jake

    After this pandemic shutdown eases there should be an incentive for job creation.
    One of the projects could be completing metrication, maybe recruit an army of those who have lost jobs to try to lay this ghost to rest once and for ever.


  8. @BrianAC

    We all know from events in recent years that it’s not the truth that matters, only what the public have read in the tabloids. Therefore if a cost was published in the Sun/Mail/Telegraph (and duplicated on Facebook) then sadly any facts produced after that point in time are irrelevant and will be ignored by the voting public.

    I suspect that we’ll be lucky if there are more than minor changes while the current administration continues.


  9. I don’t agree with the cost excuse either. But that aside what could it cost or what harm would be done if the prohibition of metric only signage was lifted and the damage done to metric signs by outlaws was punished?

    If it was announced that local communities could erect metric signage if the wanted to or replace imperial signs with metric ones when the imperial ones wore out the change would happen over just a longer period of time. The Irish did something like that. Speed limit signs changed in 2005 after it was determined most of the distance signs were metric anyway.

    Not even allowing metric only signs speaks for itself that there is an ulterior motive behind the scam and the lies.


  10. Road, or at any rate motorways, have been designed using metric units for at least 35 years. I first noticed this 35 years ago when I noticed that the markings on the motorway location marker posts give distances in tenths of a kilmetre. About 10 years ago, every fifth location marker post had a driver location sign erected next to it with the number clearly visible for drivers. In case you do not know what I am talking about, the blue signs that apear every 500 metres on England’s (but not Scotland’s, Wales’ or NI’s) motorways are called “Driver location signs”.


  11. Roads are all designed wholly in metric units. The design speed of motorways in the UK is actually 120 km/h rather than 70 mph


  12. @tonyw

    Wow! If the design speed of motorways is truly metric, imagine how easy it would be to put decals on the existing speed limit signs showing that metric number!


  13. @Ezra motorways do not actually have speed limit signs so from that standpoint the cost of conversion is actually zero, as it would be for most roads with the national speed limit the sign for that also contains no actual number so again no conversion cost (they do use numeric signs in Scotland, including a ’70’ so that’s a little more complex).

    There is, of course, the exception of the electronic signs installed in recent years, many of which may not be able to display more than two digits and there’s more than just a little justification in wondering if that might have been deliberate. But with that exception that the cost of metricating our motorways and trunk roads should be little more than the cost of changing distance signs.


  14. @Alex: The Electronic Speed Limit signs used in Australia can display up to 3 different speed limits from 10 to 110km/h in increments of 10km/h. I would imagine the signs in Britain would have a similar range.


  15. @Cliff Since Australia already has metric speed limits it’s hardly a fair comparison as it would likely be impossible for somebody to make such an error.

    I do suspect that most modern signs such as the Variable Speed Limit signs on motorways and even the older matrix signs would be able to do the job to some degree I do recall seeing some electronic signs in the past where only two digits would be possible though we would hope these things might by now have been replaced!


  16. @Alex Bailey
    Is it possible to stick on a decal with a “1” to the left of the two digit electronic display?
    If there is room, that would allow in theory for speeds up to 199 km/h


  17. What they could do is use the 2-digit displays on roads where the speed limits never exceed 99 km/h and obtain new or used units for highways where speeds exceed 100 km/h. How many of these 3-digit displays are actually needed?


  18. @Ezra while it would work for speeds such as 100, 110 and, dare I say it, 120 or 130, it might be an issue for speeds of 90 and below.


  19. I found a document which listed the total length of roads, by type, within GB, but this was in Imperial only. To get metric you had to click a link, then click another link and finally download an Excel file.

    Original document I found – Road Lengths in Great Britain

    Metric data page

    Moving on from my whinge about the metric data being buried, it turns out that within GB there are;

    3,742 km of Motorway
    47,450 km of ‘A’ road
    30,323 km of ‘B’ road
    316,082 km of class ‘C’ and unclassified roads

    So there can’t be that many of these gantries on motorways, if a change needs to be made, but what idiot would set out a specification to ensure they can only handle two digits?


  20. @ John Smith, 2020-06-20 at 21:23

    Very sad isn’t it? This document seems to be 2017, a few years after Stephen (not Philip as I thought up until this search!) Hammond I think it was, declared he wanted all transport documentation to be translated into Imperial (2012 – 2014). Eradicating it all again will never happen.
    He later was in charge of Health and Social Care, (2018 to 2019).


  21. Ezra Steinberg, 2020-06-19 at 21:11

    No, a ‘1’ decal at the front cannot work as it would always have ‘one’ as the first digit.
    Looking at a number of gantry photos it looks like a trailing ‘0 (zero)’ might work though.
    It also looks like the variable speed units are ‘bolt-ons’ to the front of the gantries, still expensive to replace but not as much as modifying the gantry itself.


  22. Who manufactures these displays such that they have a 2-digit model? One would think 3-digit would be the standard so they can be used world-wide.


  23. What hasn’t been mentioned is how this then leads on to compatibility with other equipment being used, especially on the VSL signs where speed cameras are intended to operate based on the speed limit at the time.

    I know some of the models used in the past have been sourced from manufacturers outside of the UK so there is the question: is the software on the devices dual-unit that can be switched to metric or have models used in the UK been shipped with bespoke software to handle MPH which would need to be upgraded or replaced? I would seriously hope it’s the former since it would make sense that even a British manufacturer would want to produce something that can be sold outside of the UK!


  24. Alex,

    That was my same reasoning in the previous post. If England makes these devices, why make them to 2-digits only if you intend to export them? 2-digit models are almost useless in metric countries.

    England, if they do import all of these displays may be importing US models only which are only 2-digit displays.

    US Model:

    Metric Model:

    It does appear that some metric versions are 2-digit and would be used for non-highway applications.


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