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20mph speed limits could increase pollution at city hotspots – new modelling

27 Oct 2023 3 minute read
George Street, Newport Image via Google

Nicholas Thomas, local democracy reporter

The switch to 20mph default speed limits in Wales could end up increasing air pollution levels according to a new report.

Newport council’s Air Quality Action Plan sets out how pollution will be monitored and tackled across Newport over the next five years.

More electric buses, “green walls” of vegetation, and more education in schools are all among likely strategies to cut nitrogen dioxide levels across six of the city’s pollution hotspots.

But at a meeting on today (27 October) councillors also learned that modelling for the new 20mph limits “suggests detrimental impacts from a reduced speed of traffic speed” – although the report said this should be taken in the context of “the overriding road safety benefits” of lower speeds.

Steve Manning, the local authority’s chief scientific officer, acknowledged the council’s research had “thrown up a few notional increases” in air pollution levels when the lower speed limit was taken into account.

Dichotomy

But he told the meeting of the overview and scrutiny management committee the “dichotomy” of modelling meant it was difficult to know for sure how 20mph might have an impact on pollution.

The council report also stated that “in reality it could likely lead to traffic calming, a smoother drive profile, and therefore less emissions”.

Committee member Matthew Evans questioned this.

“You’re saying the methodology [is suggesting 20mph] is going to make pollution worse, but you’re saying the reality is it won’t – how does that work?” Cllr Evans asked.

“Do any modelling, and you’ve got to try and reconcile what the modelling has thrown out at you… [with] what the real world situation might be,” Mr Manning said.

He gave the example of George Street, where modelling was done for road speeds at 30mph, but “we probably know, anecdotally, just walking around George Street, it rarely gets above 15mph between the two sets of traffic lights”.

He said the estimated impact of 20mph on pollution levels should be taken with an “open mind” because it’s “never a cut-and-dried scenario that’s been predicted”.

Neutral

Noting wider research on the lower speed limit’s impact on air quality, Mr Manning said “in truth the jury is out whether [20mph] makes a difference, one way or the other”.

“The air quality aspects associated with 20mph, in my experience, are neutral if not negligible,” he added.

The Welsh Government introduced 20mph default speed limits on September 17 this year, primarily citing road safety reasons.

It said research had found lower speeds would “reduce collisions, save lives and reduce injuries”.

The government noted 20mph limits had been deemed “pollution neutral” in one study, adding that “many things contribute to pollution levels”.

But it claimed behaviour change could also end up improving air quality.

“We believe the lower speed limits will encourage more people to choose active ways to travel and there will be fewer polluting cars on the roads,” the government said when 20mph was introduced.


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Llyn
Llyn
7 months ago

One of the many ridiculous ideas trumpeted the anti 20mph mob is the laughable idea that those unwilling to drive slower on residential areas and infront of schools; petrolheads; anti-Ulez and net zero
campaigners and idiot drivers who don’t and never have driven under 30 let alone at 20 are motivated in any way at all by environmental concerns.

Iago Traferth
Iago Traferth
7 months ago
Reply to  Llyn

I think it is a valid point and worth considering, I don’t think it will make the 20 mph rule doubtful in any way but on the other hand one should have an open mind on political issues and not dismiss arguments because they do not suit your agenda. I am for the 20 mph policy especially in built up areas and around potential danger areas like schools. I have never met anyone that opposes the 20 mph limit an urban areas and hot spots.

Peter Cuthbert
Peter Cuthbert
7 months ago
Reply to  Iago Traferth

I am somewhat surprised to hear that the new limit will increase air pollution at congestion hot spots since at first sight it seems to me that the speed limit is effectively useless. If there is nose to tail congestion, that mostly runs at under 20MPH. However, I suppose that the modelling should taking into account the likely age and emissions profile of the traffic that uses those particular roads. Does the council have that data? The important issue that so many folk seem to forget with simulation/modelling is that if you enter rubbish data then the output you get… Read more »

Paddy
Paddy
7 months ago
Reply to  Peter Cuthbert

My main issue with this story is that if lowering the speeds increasing pollution then the average speed areas along the M4 and A470 where speed is reduced significantly are also creating an existential rise in pollution for those areas, are they not?
They can’t tell us one minute that lowering speeds reduces emissions and then tell us that lowering speeds increases emissions the next, it just doesn’t make sense 🤷🏻‍♂️

Annibendod
Annibendod
7 months ago
Reply to  Llyn

“Mob” 🙄

Elen Wade
Elen Wade
7 months ago

Green energy sounds appealing, but it is terribly limited in what it can do. Green energy cannot operate agricultural machinery. It cannot make new wind turbines or solar panels. Green energy cannot exist without fossil fuels. It is simply an add-on to the current system. The reason why we hear so much about green energy is because making people believe that a green revolution is possible provides many temporary benefits. For example: The extra debt needed to subsidize green energy indirectly increases GDP. (GDP calculations ignore whether added debt was used to produce the added goods and services counted as… Read more »

hdavies15
hdavies15
7 months ago
Reply to  Elen Wade

“Green” was and remains a logical stance in response to climatic and environmental issues. However it has been hijacked and turned into a giant Ponzi scheme whereby governments and big corporations extract revenue from the public through taxation and increased utility/energy prices to fund pet projects and fill the coffers of those corporations. The whole thing needs to be reclaimed, torn from the grip of the fraudsters and returned to small scale community and localised business ownership. Then we should get accountability.

karl
karl
7 months ago
Reply to  Elen Wade

We have green energy in abundance now in Cymru, its fossils like you (awful pun I know), that prevents a future. If you can’t be bothered to grow, get out of the way and let the young do it.

Elen Wade
Elen Wade
7 months ago
Reply to  karl

The importance of diesel: The importance of diesel and jet fuel Diesel and jet fuel are important to today’s industrial economy because they fuel nearly all long-distance transportation of goods, whether by ship, train, large truck, or airplane. Diesel also powers most of today’s modern agricultural equipment. Without the use of modern agricultural equipment, overall food production would decline drastically. Without diesel, there would also be many other problems besides reduced food production. Diesel is used to power many of the specialized vehicles used in road maintenance. Without the ability to use these vehicles, it would become difficult to keep… Read more »

karl
karl
7 months ago

Aren’t those spots already under 20 mph. I smell the kind of crap Farage spouted recently. The line about prosceuting law abiding drivers, you know who are not obeying the law, by breaking the speed limit. In congested areas and city centres, the 20 mph limit probably has less value in general on pollution, it is has been aimed at streets like mine with high nitrogen dioxide leveles, outside of cities. Now for cities, getting people out of cars does make a difference, freeing space to cycle and priorities on those crosing roads also. Improved useable public transport outside of… Read more »

Linda Jones
Linda Jones
7 months ago
Reply to  karl

Surely a comprehensive public transport system fit for the 21st century is necessary to get people to get out of their cars? Cardiff doesnt have one. Cardiff bus is a third world service.

Annibendod
Annibendod
7 months ago
Reply to  Linda Jones

This. This thisity this. Best comment so far Linda 👏👏👏

Duncan
Duncan
7 months ago
Reply to  karl

Unfortunately bus company’s are revising timetables & deleting services (for whatever reason) so reduces the opportunity to use public transport. It is impossible for me to travel from my home in Swansea to work in port talbot between 7.30am to 4pm surely I’m not in a unique position.

Annibendod
Annibendod
7 months ago

As already mentioned, congestion hotspots were likely already running at lower speeds hence the pollution. It’s a bit obvious that if you’re forced to drive at 20mph or less you have to do so in 2nd or 3rd gear – your engine revs higher and you burn more fuel. What is frustrating about all of this is what we really need to do remodel and invest in our infrastructure to make active travel and public transport easier and cheaper alternatives to cars. This new law does nothing to reduce reliance on and hence car usage which is what our biggest… Read more »

Peter Cuthbert
Peter Cuthbert
7 months ago
Reply to  Annibendod

Ah, I do believe that you must be forgetting the “Power of the Market” and the “Rational Consumer”. Surely under Neo-liberal economics it should be clear that it these limits make it more difficult to get around in your car the rational consume will seek alternatives solutions… I have a bicycle for sale if there is any “Rational Consumer” seeking to get out on two wheels and into Active Travel.

Michael Ackers
7 months ago

It isn’t just congestion hotspots, though they will be worse.

My car does 20 in 3rd gear at 1500 revs. It does 30 in 4th gear at 1500 revs. Same revs, same pollution created, but at 20 mph it will take me 50% longer to cover the same distance. So 50% more pollution in the atmosphere for the same journey. Dropping the speed limit to 20 instantly means a 50% increase in pollution, and that doesn’t include irritated drivers reving their engines.

Sorry, why does it have to be remodeled?

Annibendod
Annibendod
7 months ago
Reply to  Michael Ackers

Reducing the need for cars as a mode of transport is the remodelling we need. For some, they will need their car. However our infrastructure at the moment leads many who might otherwise choose an alternative to feel that they have no alternative. That’s the remodelling we need – just like the Netherlands and others have done.

Michael Ackers
7 months ago
Reply to  Annibendod

Totally different argument. This is that 20MPH speed limits could increase pollution at city hotpots, and I’m just saying 20MPH speed limits increase pollution regardless.

William Herbert
7 months ago

This is one sure way to get rid of this looney government

DaveRealle
DaveRealle
7 months ago

“We believe the lower speed limits will encourage more people to choose active ways to travel and there will be fewer polluting cars on the roads,” …so it is a war against cars! Disgraceful.

Jeff
Jeff
7 months ago

What is the pollution 30mph vs 20 in a dynamic environment. You can’t peg the car to 30 though a 30 in a lot of urban environs, there will be disruptions to the speed. Meaning is it better to vary speed up to 20 gaining less pollution than speeding up to 30 then braking back to 5 or 0. Taking the extra energy required to make 30 and the braking to take it down, especially in oil burners. The added benefit that 2 tons of pig iron hitting a squishy meat bag does less damage at 20. This seems like… Read more »

Adrian
Adrian
7 months ago

The modelling is done on roads like Cowbridge Road west cardiff where lights sequences are set up to stop you every 300m regardless so you averaged less than 20mph already so limited difference.
If Liebour were interested in cutting emissions the lights would be set to allow continuous travel at speed limits on all main roads

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