Wales: reducing 30mph limits to 20mph could save up to 10 lives a year

12.00 | 3 April 2017 | | 9 comments

New research has suggested that if all 30mph limit roads in Wales became 20mph limits, up to 10 lives and 2,000 casualties could be prevented each year.

Published in the BMJ Journals’ ‘Journal of Epidemiology and Community Health’ on 23 March, the research is authored by Public Health Wales’ Sarah J Jones and Huw Brunt.

The research concludes that a default 20mph limit is the ‘solution to increasing public health problems in Wales’, adding that road traffic injuries, air pollution and obesity are ‘an inter-related, interdependent triad’.

Identifying interventions that will impact positively on road traffic injuries and air quality, and encourage active travel, has been described as ‘a significant public health challenge’.

The Public Health Wales paper set out to explore whether 20mph limits could be an effective intervention. The researchers reviewed the available evidence to identify the effect of 20mph limits on health and well-being, and then estimated the effect of a change to a 20mph limit on road traffic casualties and air pollution.

They found that between six and 10 lives would be saved and 1,200-2,000 casualties avoided each year, at a ‘value of prevention of £58–£94m’.

In terms of air pollution, the researchers estimate that deaths attributed to nitrogen dioxide (NO2) may increase by 63, and ‘years of life’ lost by 753. However, deaths attributed to particulates (PM2.5) – the mixture of solid particles and liquid droplets in the air – may decrease by 117 and years of life lost by 1,400.

Dr Adrian Davis, who was a founding member of the Transport & Health Study Group (UK), says this is the first time that researchers have been able to assess, at a country-wide level, the likely health impacts of a switch from 30mph to 20mph.

In an ‘essential evidence’ paper on the Travelwest website, Dr Davis says 20mph limits could be ‘an extremely important public health intervention’.

Photo: © Copyright Jaggery and licensed for reuse under this Creative Commons Licence.



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    The report is nicely presented but the evidence base for actual change (casualties or air quality) is just not there.

    David Davies, London
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    I am reminded once again of Mr. Kings assertions and support of some organisation that gave us some statistics that for every reduction of 1 mph one will see a 5 or 6 % reduction of casualty and/or death rates.

    In which case by reducing the speed limits nationally by 10 mph one should see a reduction in the region of some 50 or 60% of death and/or casualty rates. Not the low figures this report suggests.

    I must appear somewhat cynical but by merely lowering the national speed limit does not necessarily or entirely addresses the causation of many incidents which occur at speeds lower than 20 mph.

    However if we were to address the numerous dangers that insufficient space causes perhaps together with lowering some speed limits in some circumstances we may have a better chance of reducing both casualty and death rates quite considerably.

    Bob Craven Lancs
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    Reading the latest issue of Which? Magazine, I would suggest to the paper’s author that Public Health Wales would do much more good and save more lives addressing air quality and try to ban certain vehicle manufacturers particularly high polluting engine technologies. As for this academic paper, let us just say that this report does not have widespread support outside the medical fraternity.

    Agree (0) | Disagree (0)

    As it’s a real location depicted Nick, my question about pre and post speeds – notwithstanding it’s an advisory only – is still worth asking, as it would help in determining the usefulness of a 20 limit however signed, where one can see its necessity.

    Hugh Jones, Cheshire
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    Thanks Hugh – another reader has also pointed this out but as you intimate it is a library photo we selected to depict 20mph in Wales, without realising our technical error! We’ve decided not to replace the pic unless there is a clamour from readers for us to do so!

    Nick Rawlings, editor, Road Safety News
    Agree (0) | Disagree (0)

    I don’t know if the photo above is a random library photo, but it shows an advisory 20 rather than a mandatory 20 and the location and sign is obviously not typical of the residential, blanket 20 zone which is regularly discussed on this forum. I don’t know where it is, but if anyone from the Welsh authority concerned recognizes it and is able to advise us on the actual speeds (post sign) at this location, I would be interested to know i.e. did the advisory 20 sign have the desired effect? Had there been incidents which prompted the sign’s installation? Does make you wonder about the efficacy of the driving test though, when signs like this stating what should be obvious, are deemed necessary.

    Hugh Jones Cheshire
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    More wishful thinking, I think. Quoting the laws of physics is fine, we all know that slower speeds mean less kinetic energy. But to rely purely on posted speed limit reductions to deliver those lower speeds is never going to work. Let’s be honest about this, speed limits alone are probably the last thing you need if the objective is to reduce speeds!

    Charles, England
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    Surely if all vehicles travel at 20 mph then they will take half again the time taken on a journey so they will be spewing out more carcinogenic, toxic and dangerous gasses and particles for a longer period of time. Where a journey at 30 mph may take 2 hours at 20 mph it will take 3 hours. One more hour per vehicle, polluting the atmosphere and killing more people.

    What I read is words like “estimated the effects of change” and “could be an intervention” not “would be” therefore not exactly sure are we.

    If the particulates that they are referring to are from diesel vehicles then by all means get rid of diesel and that gets rid of the extremely dangerous particulates that only diesels spit out of the exhaust. That has nothing whatsoever to do with 20 mph speed limits except if one requires diesels to do a slower speed say 20 mph one will in fact multiply the degree of toxic particulates that it gives out as one is increasing the time spent on the road with the engine running.

    Perhaps one should go back to the drawing board.

    g craven
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    No mention of the increased delays, frustraation (leading to bad health) and congestion such a scheme would cause.

    Robert Bolt St Albans
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