Deeside A494 pollution below legal limit since 2020 but question mark remains over 50mph limit’s role
Roadside air pollution on the A494 at Deeside has been below the legal limit every year since 2020, almost eight years after a 50mph speed limit came into force on the stretch between St Davids Interchange and Deeside Park Interchange.
New analysis by Senedd Research, published on 3 June 2026, found that nitrogen dioxide levels fell across all five Welsh roads where 50mph limits were introduced in 2018, but said it is unclear how much of the improvement is down to the speed limits themselves.
Nitrogen dioxide is a toxic gas produced by combustion engines that can worsen asthma, lung and heart conditions, and has been linked to reduced life expectancy with long-term exposure.
The 50mph limit on the A494 at Deeside came into force on 22 June 2018, after the Welsh and UK governments were taken to court over pollution levels that exceeded legal limits.
Speed cameras to enforce the limit came into operation in October 2021.
The Welsh Government spent £3.34 million implementing speed cameras across the five sites, a figure confirmed by the then-Deputy Minister for Climate Change in November 2022.
Senedd Research analysed Welsh Government monitoring data for all five sites and found roadside pollution fell by between 42 and 63 per cent across the network between 2018 and 2024.
At Deeside, Wrexham and Port Talbot, levels have been below the legal threshold every year since 2020.
But the researchers found that background air quality — pollution not directly linked to traffic on those specific roads — also improved substantially over the same period, falling by between 32 and 41 per cent across the five sites.
To estimate how much the speed limits contributed beyond that broader trend, the researchers calculated what they called an “excess” improvement: the amount by which roadside pollution fell more than background levels.
At Deeside, that excess improvement was 7 per cent.
At Wrexham, it was 2.8 per cent — the lowest of any site.
Both figures are well below the excess improvements recorded at Pontypridd and Newport, where roadside pollution fell roughly 24 per cent more than background levels, suggesting the speed limits there had a more measurable effect.
The researchers said other local factors — including the types of vehicles using those roads and improvements in fuel efficiency — could not be ruled out as explanations for the variation between sites.
Across Wales more broadly, nitrogen oxide emissions fell by 63 per cent between 2005 and 2023, driven partly by stricter vehicle emission standards and the growth in electric vehicles.
Electric vehicles and hybrids accounted for almost half of new UK car registrations in 2025, compared with 7 per cent in 2018.
The previous Welsh Government said the 50mph limits would be reviewed if pollution dropped below the legal threshold.
The then-Cabinet Secretary for Transport and North Wales said in January 2025 that speed restrictions would be looked at if pollution levels fell sufficiently along those routes.
Pollution at Deeside has now been below the legal threshold for four consecutive years.
The new Welsh Government, which took office on 13 May 2026, has not yet stated whether it intends to review the limits.
The Senedd has accepted three petitions calling for 50mph limits on the Welsh road network to be scrapped, the most recent of which attracted 3,334 signatures and was completed in February 2026.
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