Support our Nation today - please donate here

Doubts raised on evidence used to justify reopening Cardiff’s Castle Street to private cars

16 Jun 2021 10 minute read
Castle Street in June 2021, Cardiff Picture: Alex Seabrook

Alex Seabrook, local democracy reporter

Doubts have been raised about the evidence used to justify reopening Castle Street in Cardiff to private cars.

Cardiff council is claiming that the reopening would reduce demand for private car use, and that the closure has displaced traffic and air pollution to residential areas.

The council has also called its previous modelling of forecasted increases in nitrogen dioxide levels on Castle Street due to the planned changes “incorrect”.

The cabinet is due to approve reopening the road to private cars, after a year of closure, on Thursday, June 17. Doubts were also raised about how long the ‘provisional’ reopening will actually last.

The road will open to private cars this autumn, with two lanes for general traffic, and one bus lane. The new bike lane will be kept, but the pavement on the south side of the street will be made narrower. Before its closure, the road had four lanes of traffic.

This work was originally going to be paid for using £300,000 of clean air funding from the Welsh Government, meant for councils to cut air pollution. Cardiff council has now backtracked, and said it will pay for the works itself.

Councillor Caro Wild, cabinet member for strategic planning and transport, said: “The modelling showed that while air quality issues were generally better off across the whole city, there were some areas of concern that officers had, particularly around some of the residential areas around the city centre.”

Cllr Wild was giving details of the rationale as council bosses were grilled this week on the planned changes by both the economy and environmental scrutiny committees on Monday, June 14, and Tuesday, June 15.

One argument the council is making is that the planned changes will reduce demand for private car use. But that’s compared to before the pandemic and the closing of the road. Reopening Castle Street however could induce demand for more people to drive cars.

Cllr Peter Wong said: “How do you square reopening Castle Street to private traffic against the proven issue of induced demand? You don’t reduce car use on a long-term basis by building new roads or reopening roads. You don’t reduce demand by reopening roads.”

A public consultation held over the spring gave two options. Option one was to reopen the road to private cars, while option two was to keep the current arrangement of open to only buses and taxis. 53.8 per cent chose option one, while 33.8 per cent chose option two.

Jason Bale, the council’s programme manager for clean air, said: “Option one does try to reduce demand. We’re taking nearly 50 per cent of the capacity for traffic out of it, compared to the pre-Covid baseline. In terms of air quality on Castle Street with that option, it’s an improvement of up to 32 per cent of the concentrations of nitrogen dioxide pre-Covid.”

‘No evidence’

Another issue is how the closure has displaced traffic and air pollution to nearby residential streets, like Cathedral Road in Pontcanna, as drivers were diverted from their normal route to get from the west side of the city to the east side, or vice versa. But data from air pollution monitoring stations does not back up the claim that residential areas have been affected.

Cllr Owen Jones said: “I notice that no street is showing higher levels of nitrogen dioxide than pre-pandemic. So no street, by the looks of it, is worse now with Castle Street fully closed.

“The justification of having to reopen Castle Street is because traffic has been diverted into residential areas. From the evidence provided today, I can see no evidence that traffic is being diverted any worse than previously into residential areas.

“This argument has been touted for the justification that it’s been diverting [traffic] into residential streets, which a lot of people are quoting on the internet. Adamsdown has been one of them, but I have no visual or nitrogen dioxide evidence of that.

“Is there any evidence that traffic is worse now with Castle Street closed than pre-pandemic, in areas like Grangetown, Riverside and Adamsdown?”

Cllr Tom Parkhill also asked: “Did the closure of Castle Street worsen air quality levels elsewhere in the city?”

Council bosses said the data actually shows nearby residential areas have seen recent improvements in air quality, due to lockdown and fewer people driving in general. The argument instead relies on uncertain transport modelling, assuming how people will drive in future. Modelling shows nearby roads could see reduced air pollution with the reopening.

Mr Bale said: “The 2020 data we have across the city is skewed somewhat because of lockdown, so it’s an unfair comparison to say ‘did it worsen air quality’. Even if we hadn’t closed Castle Street, it would have improved across the city because the traffic wasn’t there for a number of months.

“We haven’t seen any breaches elsewhere across the city. Average levels on Cathedral Road are compliant.”

Andrew Gregory, the council’s director of planning, transport and environment, said: “I don’t think any of the communities are close to pre-Covid levels. There are uncertainties about some of the impacts on some of the residential areas, in terms of increases of traffic congestion and increases in terms of air quality.

“Only as analysis takes place will we understand the full implications of the air quality factors at play across the city. We’re trying to see this as part of a longer term plan to move to a much better scenario for the city as a whole, but also some of the key communities adjoining the city centre, and also the city centre itself.”


A third issue is the modelling of nitrogen dioxide levels on Castle Street. When the consultation was launched last March, the council published an information pack to help the public make an informed decision on which of the two options they preferred.

This pack showed the planned changes would increase nitrogen dioxide levels by 52 per cent, from 21 micrograms per cubic metre currently to 32 micrograms with the planned changes. However, a council spokesman has now said this modelling is “incorrect”.

More recent modelling has revised these figures down to an increase of 40 per cent, from 20 micrograms currently to 28 with the planned changes. The new figures are due to transport modellers assuming large reductions in car journeys, which weren’t previously factored in.

A council spokesman said: “[The changes] include responses in terms of mode, destination and time-period choice, in reaction to changes in travel costs. This results in reductions in the number of total car trips made in the city centre, in response to the removal of capacity and changes to allowed movements on the highway networks.”

Also thrown into doubt is how long Castle Street will remain reopened to private cars, with council bosses hinting the road could be closed again in future. The council wants to assess the actual impact of the reopening, as well as how traffic will change after the pandemic and once the bus station is finally finished.

Cllr Wild said: “I see this next stage as being a relatively temporary one. We want to continue to test to see how we can get fewer cars in general that will allow us to set aside more road space in the city centre.”

Mr Gregory said: “It’s still a provisional arrangement. We’re not talking about eight months of fundamental highway reconstruction. Rather it allows us to move forward into the provisional scheme we’re proposing.

“We have a very dynamic scenario around the city centre for two particular reasons. One is post-Covid, we don’t know how people are going to respond coming back to work and coming into the city centre. Also we have a very dynamic and uncertain situation because there’s so much work taking place in the city centre at the moment.

“Given those two current positions — post-Covid settling down and settling down the city centre post this development work — we consider it’s not a sensible position to take at this point to implement a permanent scheme. So we’re proposing a provisional scheme.”


In a lengthy statement, the council said several factors needed to be balanced like cutting air pollution levels on Castle Street to within legal requirements, and potentially increasing traffic in surrounding streets and rising pollution in nearby residential areas. Both options bring pollution on Castle Street to within legal limits, which the council is bound to do by law.

A spokesman said: “Option one replicates the scheme included in the council’s Clean Air Plan, that was approved by Welsh Government’s independent expert panel and signed off by ministers when the plan was approved in December 2019 before the pandemic struck.

“However, the latest modelling, undertaken by expert consultants that specialise in transport and air quality, shows that pollution levels could rise in 34 of 42 streets and key routes into the city if cars are completely displaced from Castle Street and option two is adopted by the council.

“While the modelled rise in surrounding areas is within legal limits, there are clear concerns that any rise of air pollution in residential areas, in favour of achieving lower levels of pollution on non-residential Castle Street, is one that needs to be carefully considered before cabinet takes a decision on Thursday, June 17. This is particularly important as many of these residential areas already have relatively poor levels of air quality.

“There are also concerns around what traffic flow will look like once lockdown has been lifted and things return to normal. If we see an increase of car use then pollution levels in surrounding residential streets could possibly rise higher than currently projected.

“Consequently, the council wants to gather more data on traffic flow across the city centre as commuters return to work and visitor numbers return to normal after the pandemic. This up-to-date data on post-pandemic traffic flows will then be used to inform plans to further reduce air pollution and congestion in the city. This council is committed to improving public transport, cycling and walking options across the city making the air in Cardiff cleaner for everyone to breathe wherever they live.

“If cabinet chooses option one tomorrow, it is worth remembering that Castle Street will not reopen as it was pre-Covid. Three lanes of traffic will be reduced to two lanes of traffic, while a dedicated bus lane and the two-way cycleway will both remain. This should, according to modelling, and the current trend of people continuing to choose to travel by sustainable forms of transport, reduce general traffic on the street to around 50 per cent of pre-Covid levels at peak times.

“This would meet a legally binding requirement to lower pollution on the street to acceptable limits in the shortest time possible and represents the council’s original plan for the road as set out in the Clean Air Plan produced by Cardiff council and subsequently approved by Welsh Government in 2019.”

Cabinet reports previously said the works on Castle Street would be paid for with clean air funding by the Welsh Government, meant for councils to reduce air pollution. But the council has now denied this would happen, and the council would pay for the works itself.

The spokesman said: “Option one for Castle Street, which could be temporarily put in place while up-to-date data is gathered and further modelling is carried out to establish the best way forward, will not depend on Clean Air funding from Welsh Government and can be funded from existing Highways related budgets.”

Support our Nation today

For the price of a cup of coffee a month you can help us create an independent, not-for-profit, national news service for the people of Wales, by the people of Wales.

Notify of
Newest Most Voted
Inline Feedbacks
View all comments
Morris Dean
Morris Dean
3 years ago

“Let’s allow private cars then stop them again”

Transport planning of the madhouse.

Just keep them stopped and help make Cardiff city centre liveable and clean

3 years ago
Reply to  Morris Dean

Just as mad as persisting with major building in and around the centre of the city thus keeping up the pressure for commuting and general people movement. Out of town, even out of county, would make more sense but our dear Capital City has to grab everything it can reducing the rest of South Wales to dormitory status.

Chris Groves
Chris Groves
3 years ago

The key sentences:

‘“There are also concerns around what traffic flow will look like once lockdown has been lifted and things return to normal. If we see an increase of car use then pollution levels in surrounding residential streets could possibly rise higher than currently projected.’

Like Pete Wong said – you open Castle St, you induce more traffic. Those people who think that allowing cars back on Castle St will somehow magically erase air pollution and congestion from Riverside, Grangetown, Canton and Pontcanna could be in for a nasty shock.

Our Supporters

All information provided to Nation.Cymru will be handled sensitively and within the boundaries of the Data Protection Act 2018.