Know your speeds – the voice of experience

When one day the British roads are converted to metric units, drivers will need to get used to distances that are measured in kilometres and speeds that are measured in kilometres per hour (article contributed by Martin Vlietstra).

The author first experienced such a conversion in South Africa in the early 1970s. Initially everybody paid lip service to the speed restrictions, then the Arab-Israeli War broke out and in its wake came a fuel crisis. The South African Government’s reaction was a draconian reduction in the national speed limit (which was reduced from 120 km/h to 80 km/h), fuel station closures at night and over the weekends and a large increase in speeding fines -in today’s terms, the minimum speeding fine would have been GB£1,000.

South African cars did not have dual-unit speedometers and anybody who had a car that was more than two or three years old had to learn how to convert between mph and km/h very quickly. I never forgot the small set of conversion values that I had to memorise.

Reflecting on this in recent years, I saw the value of having a few easy-to-remember conversion values and this set me thinking â?? then I came up with the sequence:

30 – 50 – 80

What does this mean? Quite simply:

30 mph = 50 km/h (approx)

50 mph = 80 km/h (approx)

This sequence can easily be extended by one digit on either side to give:

20 – 30 – 50 – 80 – 130

And we get the following set of conversions:

20 mph = 30 km/h (approx)

30 mph = 50 km/h (approx)

50 mph = 80 km/h (approx)

80 mph = 130 km/h (approx)

It would be a matter of debate whether a ‘know your km/h’ campaign based on this sequence should have three, four of five numbers. No doubt psychologists or educationalists would be able to assist.

13 thoughts on “Know your speeds – the voice of experience”

  1. So does that mean that all adult drivers in the UK will have to go to ‘metric lessons’?
    I stand by one thing though; the Imperial system on our roads will last for a long time to come for several reasons:
    1) The art of driving is not something where you have a lot of time to think. People used to driving at 50 mph might see a sign saying ’50’. As they are used to using miles, will they automatically convert 50 km/h to 30mph and then slow down? All in a few seconds? Imagine the chaos if people drove down the motorway and saw signs for ‘120’.
    2) Does our government have the money to waste on changing the road signs? I am sure the UKMA’s proposed cost of it all is far short of the realistic amount. We cannot as a country afford to waste good money on it, even though other countries have.
    3) The main argument for the metrication of the road signs is that almost every other country in the world uses them. So what. In my view, they are traditional and I do not see why we should change just because foreign tourists get confused when they drive here. If they want to drive here, then they should prepare or not come.

    I do not think that the road signs are a high priority for this country today and if you look, you will see many people who are against the kilometre.
    I think the mile and yard is here to stay for now.


  2. Are British drivers really so stupid that they would interpret 120 as mph if the government announced it was metricating roads? British drivers abroad do not interpret French signs as in mph otherwise there would be chaos in Calais!

    Properly prepared metric transitions in Canada, Australia and Ireland have shown that people have no difficulty coping. Those countries also managed their costs well when converting their roads unlike DfT’s preposterous costings.


  3. Tabitha Jones claims that  British drivers can not adapt to metric driving. Maybe Tabitha would like to explain why drivers in the UK would interpret km/h signs as miles when such a thing did not happen in other countries that metricated. Ireland being the latest in 2005. The people don’t need metric lessons. They were taught metric in school, they already know it, even if some pretend to be ignorant.

    Is Tabitha also saying that the UK is a 3-rd world country? All these other countries that metricated managed to do it and the costs weren’t prohibitive.

    One doesnt change for the sake of foreign tourists, but to put a system in place that everyone, including the natives can understand easily. Surveys and tests have already proven that people who claim to know imperial units, really don’t.


  4. The previous comment [from Tabitha Jones] makes we wonder how they managed to pull off the change-over to metric signage in the Republic of Ireland? All that seems to have gone without a hitch.


  5. I think if we’re going to discuss the costs of a change over, and the waste of money then it’s the DfT that’s wasting money already. Roads are designed and built in metric units. Maps are marked in a metric grid. But for the last 3 decades the DfT has continued to place obsolete yard/mile signposts all over our roads. That is where the money has been wasted.

    I grew up in this country, and I was taught at school that distance is measured in metres. When I learned to drive I had to learn about a different system that measures short distances in multiples of 0.9144 m and a long distances in multiples of 1.609344 km. I know that was used for a long time in the UK, but can anyone really claim to understand it?


  6. I doubt anything I write will change the mind of Tabitha Jones but I will give it a try.

    Like it or not the UK is part of a much bigger world. Everyday 10,000 lorries driven by drivers from outside the UK drive on our roads. Everyday 1000’s of buses and lorries driven by british drivers drive elsewhere in the EU. In my mind this alone is excellent cause for one system of speed limits EU wide.

    I’m 35 and was educated in metric, as were the majority of drivers on UK roads. Our roads are designed using metric measurments and signs are placed using metric measurments. It’s not surprising that more and more information signs put up by private companies use metric distance and not imperial. They want the majority of people using our roads to understand the message the sign is presenting. It’s time the DfT got their act together and joined the rest of us in the 21st century.


  7. I would like to echo Robert’s comment. If anyone needs ‘metric lessons’ it is the senior staff at the UK Department for Transport (DfT). Since 1965, when the UK Government gave its support to the move to metric units in British industry, over 40 countries have made the changeover to metric road signage. There must surely be enough experience around the world to show the DfT how to do this job safely, efficiently and economically.
    But they should not delay, because first-hand knowledge will be lost. Or is this the DfT plan?


  8. Here in Sydney the major roads have a 70 km/h speed limits. Some people have a device in their motorcars – an alarm goes off when the car is above 70. A good way to avoid speeding fines. Also aren’t motorcars destined for the UK market have dual marking on their speedometers? So you would not need to convert.
    I would also like to add, here in Aus we have your British motorcar programs TOP GEAR and 5th GEAR. The presenters review a car and say it has X amount of Horse Power, and can do X amount of miles per gallon!!
    I just think why do our networks buy such rubbish. I want to throw something at the tellie.


  9. Tabitha, like many others in the anti-metric camp, love to use cost as a deterrent to conversion. Has she thought though about the additional cost we pay as motorists because the motor industry has to manufacture speedos specially for the UK market? What about the extra paid out for speed cameras specially converted to use MPH? (Gatso are Dutch and Truvelo are South African so their home markets are metric). I’m sure SatNavs would be cheaper if they didn’t need to have miles on them and (despite what the DfT seem to think in their estimates of changeover costs) maps would probably be cheaper too as map publishers would be able to use the raw metric data from Ordnance Survey instead of having to convert to imperial.

    And while we’re on costs… look at the money that the government want to waste on trials for road-pricing schemes which are extremely unpopular with voters (as the recent Number 10 poll and the current campaigns in Manchester show), these are considerably more expensive than metric conversion would be. Even the DfT’s inflated estimates are only a small fraction of what it’s going to cost the country to hold the 2012 Olympics!

    And none of this takes into account what it has cost to educate every schoolchild since the late 1960’s in a subject which they are being denied the opportunity to use.


  10. Rule of thumb:

    The distance to the vehicle in front (in metres) should be at least half the speed (in km/h) at all times (e.g. at least 60 meters at 120 km/h). This corresponds to a “lead time” of just under 2 seconds. As a reference: The white-and-black reflection posts to the right have a distance of 50 m to each other. Again, the fact that the car in front is illegally occupying the left-hand lane when the right-hand lane is free is not a valid excuse.

    I can’t envision this simple relationship in FFU.


  11. As I was driving under the overhead gantries on the M25 and M42, I noticed that the variable speed limit signs only seem capable of displaying up to two characters, therefore would have to be replaced should are roads be converted to km/h as the maximum speed limit they could show is 99. Isn’t this a little short-sighted of the DfT?


  12. In answer to Michael Hawkshaw’s point, I don’t think this is an insurmountable problem unless speed limits are raised to 200 km/h. I don’t know many bulbs the dot matrix displays use, but you only need two columns to add a “1” and a space. On a hypothetical set of two 5×7 characters, 130 could be shown as:

    @_@@@ _@@@_
    @____@ @___@
    @____@ @___@
    @_@@@ @___@
    @____@ @___@
    @____@ @___@
    @_@@@ _@@@_


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