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news
20mph sign (CC licensed by EdinburghGreens via Flickr)"Far more pleasant for walkers and cyclists": 20mph speed limit analysis hailed "astonishing", with drivers' journeys just 45 seconds longer
Initial analysis of the impact of widespread implementation of 20mph speed limits across Wales last week suggests a "dramatic" change in traffic speeds, with the results hailed "astonishing and far greater than would have been predicted".
Rod King MBE, a campaign director at 20's Plenty for Us told Wales Online he hopes the move will make routes "far more pleasant for walkers and cyclists", his comments coming as a report by transport and public health data analysts Agilysis showed an on average reduction in vehicle speed on new 20mph routes of 2.9mph.
Agilysis' Richard Owen said the results were "astonishing" and showed that Welsh drivers had "on the whole" accepted lower speed limits and "have changed their behaviour accordingly".
"There will remain some drivers who choose to break the limit by significant amounts but the drop in speeds on the fastest urban roads has been marked," he said.
Agilysis undertook the research after the implementation of the default urban speed limit on 17 September, and collected GPS data from mapping company TomTom to retrieve and analyse speed data within 24 hours of the change.
Looking at the data anonymously provided, Agilysis studied "a very significant sample and more than sufficient for this type of analysis" across a selection of vehicle types — privately owned cars, vans, plus commercial vehicles.
In total, 491.8km of roads that changed from 30mph to 20mph, were analysed across areas such as Cardiff, Newport, Swansea, Wrexham, Rhyl, Merthyr Tydfil, Lampeter, Bangor, Haverfordwest and Newtown. Minor local roads and quiet residential roads were excluded from the analysis as they do not have sufficient sample sizes for the time periods selected.
The headline figure pre-implementation of 20mph speed limits was the average weighted median speed across all the routes was 22.7mph, this dropped to 19.8mph post-implementation.
[Table: Agilysis]
In Cardiff the average weighted median speed dropped from 22.6mph to 19.7mph, while the biggest drop was seen in Rhyl & Prestatyn and Wrexham where the average speeds dropped from 23.2mph to 19.6mph, a reduction of 3.6mph from before the implementation.
[Table: Agilysis]
The report concluded the change in speed had been "dramatic" and suggested that compliance is "very good". By using results from Cardiff and Wrexham, the report suggests that drivers' journey times were, on average, between 45 and 63 seconds longer.
"The analysis period covered the 6am to 6pm period and compliance is expected to be lower outside of these times," it suggested. "Fewer vulnerable road users (cyclists and pedestrians) are likely to use the roads at these times however and the impact on those killed or seriously injured may be lower. Nevertheless, there are opportunities using this approach to review compliance at different times of the day."
Rod King of 20's Plenty for Us added: "Our experience from so many implementations across the UK tells us that 20mph limits work, and they work particularly well on the faster urban roads.
"They are not a silver bullet, but do reduce speeds to make streets far more pleasant for walkers and cyclists, they lower faster speeds and produce a more consistent flow of traffic. This in turn makes it safer for all road users. A default urban/village 20mph limit is key to liveability and community life whilst at the same time retaining mobility for all. Well done Wales."
Dan is the road.cc news editor and has spent the past four years writing stories and features, as well as (hopefully) keeping you entertained on the live blog. Having previously written about nearly every other sport under the sun for the Express, and the weird and wonderful world of non-league football for the Non-League Paper, Dan joined road.cc in 2020. Come the weekend you'll find him labouring up a hill, probably with a mouth full of jelly babies, or making a bonk-induced trip to a south of England petrol station... in search of more jelly babies.
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122 comments
Like the one on inverleith row (20 limit) a couple of weeks ago?
"The car flipped up, flew across the road, and then landed on its roof, wiping out the bus stop."
Must have got caught by a crosswind.
It probably had to jump out of the way when a cyclist suddenly appeared in front of it.
You know what 'average' means right?
2.9mph is quite a significant reduction.
However, a huge benefit that misses is the significant reduction in the proportion of serious speeder - who will now be doing 25-30mph rather than 35-40mph.
The numbers are in the Interim Monitoring Report.
2.9mph is quite a significant reduction.
However, a huge benefit that misses is the significant reduction in the proportion of serious speeder - who will now be doing 25-30mph rather than 35-40mph.
The numbers are in the Interim Monitoring Report.
It's not really - it's not even average walking pace.
But it is an average - which means that it still takes account of those speeding drivers - and it's clear that you cannot average 19.7mph without some drivers going over the speed limit. Whereas before, many were clearly not exceeding the speed limit, due to a much lower average speed vs the actual speed limit.
It simply shows that this was a pointless exercise in money wasting
That change in average speed has cut out the peak speeds. An average is 19.8 for a limit of 20 versus an average of 22.7 for a limit of 30 effectively reduced the peak differential from 7.3 to 0.2 mph.
Much less acceleartion and braking, better both for safety and for the environment.
Yes so of course the peak speed could be higher - but it makes very little difference to actual road safety because the "actual" average has only dropped 2.9mph - which means that people are still going higher speeds - maybe just less of them.
Besides, as I mentioned - it's nigh on impossible to think that everyone is staying under 20mph with an average speed of 19.8mph overall - for it to be an average, there must be still nearly 50% who go over the speed limit in any case.
If it really was pointless, it might as well stay then since money has been spent and undoing it to get the 2.9 back would be as expensive again.
Nope not true and if it was that would have always been the way you set speed limits, the X over the limit thing sounds intuitive, but it's a myth the DfT addressed this once stating.
"It is a common but mistaken belief that drivers allow themselves a set margin over the prevailing speed limit, and that if a limit is raised by 10 mph, they will travel 10 mph faster. In fact, an increase in an unrealistic speed limit rarely brings an increase in traffic speeds. It is much more likely that there will be no change, or even a fall."
Just to show the level to which this is not true I compared speeds and levels of compliance to various sections of the more unrealistic 20-limits in Monmouthshire to every urban 40-limit road in Cheltnham and Gloucester.
This also shows that higher limits get much more respect and lower limits causes them to be held in contempt.
Meaningless: without a comparison of the road types, usage relative to capacity, etc, this shows nothing. I can show you stretches of road with higher limits where effectively zero drivers obey the limit, and 20 limits where nobody gets anywhere near.
I offer you this thought: if you make cider with oranges, it's not as good as the real thing. Therefore oranges are not good apples. About as logical as your post.
Well, take a look on streetview, I'd say they're in some sections they're pretty simalar road types.
These 40-limit roads there are repeaters activly telling drivers they can go faster and they still don't, the repeaters do more to warn pedestrians that it's not the sort of road to run into.
If someone was already doing 35-40 in a 30 I doubt they ever slow down for a 20 zone, unless there are unavoidable speed bumps in which case it's last of the late brakers in an attempt not to get air time.
In all your various reincarnations you have struggled with statistics. As for 'herd of donkeys' you would be better off with Led by Donkeys. https://twitter.com/ByDonkeys/status/1705455729514012920?t=7Dk-3GFnyFM4D...
Ignoring the 20mph speed limit briefly - it is interesting that TomTom holds and can process the speed of its users like this*. I know cycling computers have been used in the past to prove the speed of a cyclist before a collision - this would suggest the same could be done for vehicles? I can't recall ever seeing that kind of analysis being presented in court.
*I realise it is a third party that has processed it in this instance, but the data is there
Google also holds this information - and a lot more. In that you dont need to be using the navigation funciton. Current hurdles in using it are based around gps accuracy - the proximity of (for instance a minor road running next to a motorway). For a definable stretch of identifiable road - with some limited developer skills you can access annonymous speed data for vehicles (cars with mobile phones in them)
There is a Github that can be downloaded that uses GPS signals to determine vehicle speeds via triangulation. It cannot access the device though and the load out has to have a specific road/street named and there is a fee I believe.
Github.com/BerkshireCar/SpeederBot
There is a Github that can be downloaded that uses GPS signals to determine vehicle speeds via triangulation. It cannot access the device though and the load out has to have a specific road/street named and there is a fee I believe.
Github.com/BerkshireCar/SpeederBot
Cyclists know that there is little point for car drivers to accelerate to the next set of traffic lights or junction. Also there is no point overtaking a cyclist, even a slow one as one will probably change routes within a few 100m and the driver will gain 5 seconds at best.
Are these based on free-flowing traffic speeds or the speeds of all traffic?
Normally you look at the free-flowing figure to get the more realistic result.
I think the Atkins report showed an average drop of 1.3mph but for a very high increase in non-compliance.
Traffic speeds are mostly dictated by the design of the road and the conditions at the time, not by speed limits, this is more down to how our system 1 brains function.
People who genuinly drive too fast or discoutiously to pedestrians and cyclists are not doing so due to a lack of signage to tell them not to.
Agree in part - the best way to ensure people adopt appropriate speed is to ensure the design of the road conveys this itself. However - due to the "anchoring" psychological effect numbers are important. Also if a even a few drivers are sticking to the speed limit it will tend to bring others down.
It's also unlikely that that level of infra change could be accomplished in less than decades!
Don't have the links to hand but IIRC a measurable effect created by just changing numbers on the signs sign *was* reported by some studies cited when Scotland was looking at this idea.
Re: traffic speeds, what you say may be true in many places, but my recent experience of the M4 in Wales was that nearly all drivers were sticking to the 50mph limit, thanks perhaps to the many speed cameras. The traffic ws also flowing very smoothly and by comparison with the English part of the M4, driving was much less stressful.
That's because there's an average-speed camera forcing people to do it. Also, while 50mph might be slower than the speed most people would go in the absence of a speed limit there, it's not so slow compared to the road design that it's unintuitive.
The road safety charity Strongtowns made a video explaining why you get so much non-compliance and it's not down to people needing time to get used to it or willful disregard of the law. https://youtu.be/NDYQaa3K_BA?si=toSgzZZcFAmAnoCg
It's amazing how many people don't seem to understand average speed cameras though - braking immediately before each camera.
It's well known that at least 80% of people are below average intelligence.
What about the other 30%?
At our place, one of the bosses is demanding to know why 40% of sick days are occurring on Mondays and Fridays.
The lead investigator told us "collecting the bears' leavings, recording locations and times, lets us build a pretty good picture of which individuals are about, where in the wood they are ranging, and also some secondary data about family members they are associating with and their diet. We're getting better at determining how long it has been on the ground - we can date to an accuracy of about 12 hours, but temperature and rainfall all have to be taken into account.
A lot of teams swear by observation, but the problem you have there is you got to spend a lot of time at a fixed location and you cannot be 100% sure which individuals you are seeing at different times. We use cameras in some locations, but you have to either get lucky or leave ground bait to get any useable shots.
I guess we're gonna be collecting bear leavings for a little while yet."
Most cyclists know this, as they've witnessed MGIF drivers simply get to the next set of traffic lights earlier. The traffic light sequence is what truly dictates average traffic speeds
Traffic lights and massively....other cars. As soon as I get into a built up area its 99% of the time the cars that slow me down.
I was coming back from the airport in the car the other night and we were stuck behind someone doing 30 in a 60 but there was nowhere safe to overtake because a car takes up a whole lane on the road and is travelling at 30mph. If that was a bike we would all have been past them within a few minutes. As it was, we were all stuck behind this one car for at least 20 minutes.
I would wager a very large sum of money that if you totted up all the time car drivers spend stuck behind bikes vs stuck behind cars it would be in the low minutes per month for bikes and multiple hours per month for cars.
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