Default 20mph for Wales
Re: Default 20mph for Wales
Drop in frequency and severity of collisions is only one part, perhaps the most easily countable part, of the benefits there should be from lower speeds. Less noise and less air pollution could also be expected, and of course are measurable. Increase in walking and cycling will probably lag and are harder to measure accurately. But some of the most important things are almost impossible to measure; such as decrease in social atomisation, or simply are never measured, such as increase in ease of crossing the road (and people attempting to do this).
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Re: Default 20mph for Wales
On the significance of the casualty figures. From 20s plenty campaign.
Re: Default 20mph for Wales
Are those year on year changes or all compared with the same baseline?
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
There are two kinds of people in this world: those can extrapolate from incomplete data.
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Re: Default 20mph for Wales
Year on year changes as I understand it.
Was from a Facebook post
We have done further analysis on the Welsh urban/village casualty data going back 20 years. By charting the annual %age change from the previous year it shows that, apart from Covid, the 28% reduction after implementing the default 20mph in 23/24 is exceptional. Note that usually 40mph+ and 20/30mph will follow the same pattern, but in 23/24 it was markedly different. The 23/24 reduction is also 2.3 times greater than any previous reduction in casualties. #20splenty
Is be amazed if that doesn't pass any standard significance test, but I guess the question as to whether it sustains is open.
Re: Default 20mph for Wales
The other thing that stands out on that graph is the increase in casualties as we "returned to normal" after covid.
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Re: Default 20mph for Wales
The thing about statistical significance is that it is a very strong test. What it says is that given a particular set of figures - and considering no other evidence whatsoever - is there less than a 5% probability of the result being a random event. It is basically similar to the "beyond reasonable doubt" test at criminal trials.roubaixtuesday wrote: ↑3 Feb 2025, 12:42pm Is be amazed if that doesn't pass any standard significance test, but I guess the question as to whether it sustains is open.
Unfortunately the common usage of the word "significant" means that even strong evidence that doesn't quite meet the test of statistical significance is often claimed to be "insignificant" or even non-existent by political opponents wishing to avoid uncomfortable research findings.
If, given a very extensive intervention over an entire country with a very marked result does not meet the test of statistical significance then it is unlikely that sufficient data could be collected for any highway intervention whatsoever to meet the criterion. And if they really think that it will need 3 years of data to judge the efficacy of the scheme then they really need to stop any reversions to the limit till September 2026.
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Re: Default 20mph for Wales
I'm very confident that if covid year is excluded as an outlier, that meets the standard 5% test for significance.Pete Owens wrote: ↑3 Feb 2025, 2:48pmThe thing about statistical significance is that it is a very strong test. What it says is that given a particular set of figures - and considering no other evidence whatsoever - is there less than a 5% probability of the result being a random event. It is basically similar to the "beyond reasonable doubt" test at criminal trials.roubaixtuesday wrote: ↑3 Feb 2025, 12:42pm Is be amazed if that doesn't pass any standard significance test, but I guess the question as to whether it sustains is open.
Unfortunately the common usage of the word "significant" means that even strong evidence that doesn't quite meet the test of statistical significance is often claimed to be "insignificant" or even non-existent by political opponents wishing to avoid uncomfortable research findings.
If, given a very extensive intervention over an entire country with a very marked result does not meet the test of statistical significance then it is unlikely that sufficient data could be collected for any highway intervention whatsoever to meet the criterion. And if they really think that it will need 3 years of data to judge the efficacy of the scheme then they really need to stop any reversions to the limit till September 2026.
Re: Default 20mph for Wales
What surprised me was how small those "corrections" were.
If you drop 50% due to "one off" event.
To get back to where you where you need to grow by 100% the next year.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
There are two kinds of people in this world: those can extrapolate from incomplete data.
Re: Default 20mph for Wales
[The casualties were only down 28%! But i think you know that ...

Yes, it is a little surprising. I think a lot of people don't realise how slowly UK traffic levels have recovered. Presumably this is mainly down to increased WFH, but i'm just speculating.
it's like our brains don't remember 2019 accurately, we just note that this year is more than last year, etc etc .. And we only really notice exceptionally busy days/weeks - we notice the quiet days less.
A quick google gives:
n.b. that's only for 2023.Main points. Road traffic volume in Wales in 2023 increased by 2.1% compared to 2022, to 29.8 billion vehicle kilometers (bvk) but remained around 2.9% below pre-pandemic levels (30.7bvk in 2019).
29 Aug 2024
Re: Default 20mph for Wales
In '21 there were still lockdowns, and more I think in Wales than in England (not sure about Scotland or NI). But also in 20/21 casualties continued falling on 30mph roads but rose on 40s.
Re: Default 20mph for Wales
I was using easy numbers for illustration - not suggesting they were on the chart.mattheus wrote: ↑3 Feb 2025, 4:16pm[The casualties were only down 28%! But i think you know that ...]
Yes, it is a little surprising. I think a lot of people don't realise how slowly UK traffic levels have recovered. Presumably this is mainly down to increased WFH, but i'm just speculating.
it's like our brains don't remember 2019 accurately, we just note that this year is more than last year, etc etc .. And we only really notice exceptionally busy days/weeks - we notice the quiet days less.
A quick google gives:n.b. that's only for 2023.Main points. Road traffic volume in Wales in 2023 increased by 2.1% compared to 2022, to 29.8 billion vehicle kilometers (bvk) but remained around 2.9% below pre-pandemic levels (30.7bvk in 2019).
29 Aug 2024
My memory of 2020 is not positive, though it probably should be, I didn't die.
Traffic levels did drop, for obvious reasons, and whilst 20/12 also had similar restrictions to travel.... But the major drop really didn't get "corrected" at all.
So that's a 22% drop for covid, then another 8% the year after, followed by just 6% and 5% (that's only back to 80% of 2018/9).
Maybe that's just picking up the longer term trend... the growth in intermediate years is actually just an artefact of the collapse in covid.
Then we get another 28% drop takes us to 58% of the 2018/9 level.
That's massive.... properly massive.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
There are two kinds of people in this world: those can extrapolate from incomplete data.
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Re: Default 20mph for Wales
It's a bit mind bending to think that some of us may be alive today purely because of the Covid epidemic. The commuter driver that was "destined" to knock us off never made the journey because he was told to work from home.
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Re: Default 20mph for Wales
Quite. Added to that some of us might live longer because we cycled (gaining improved health and healthy habits) during the lockdown periods. Maybe not living in such a dangerous place as Wales is a plus too?deeferdonk wrote: ↑4 Feb 2025, 7:39am It's a bit mind bending to think that some of us may be alive today purely because of the Covid epidemic. The commuter driver that was "destined" to knock us off never made the journey because he was told to work from home.

Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
Re: Default 20mph for Wales
Dangerous in Wales? I must have a look out of the window to see what on earth is going on...Carlton green wrote: ↑4 Feb 2025, 8:48amQuite. Added to that some of us might live longer because we cycled (gaining improved health and healthy habits) during the lockdown periods. Maybe not living in such a dangerous place as Wales is a plus too?deeferdonk wrote: ↑4 Feb 2025, 7:39am It's a bit mind bending to think that some of us may be alive today purely because of the Covid epidemic. The commuter driver that was "destined" to knock us off never made the journey because he was told to work from home.![]()

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