Wales’ 20mph speed limit did not improve air quality, study finds
Wales’ 20mph speed limits made little difference to air quality, a study funded by the Welsh Government has found.
Differences in nitrogen dioxide (NO2) levels on roads inside and outside the 20mph zone were insignificant, a report published on Friday said.
Out of four sets of sensors deployed as part of an official study, three recorded small increases and decreases that were within the sensors’ margin of error, making the findings statistically meaningless.
Natasha Asghar, the Welsh Tories’ shadow transport minister in the Senedd, said: “This blows a huge hole in the argument that lower speed limits will improve air quality.
“With two locations helping air quality and two hindering air quality, I don’t believe that the data can accurately ascertain whether lower speed limits are making a difference to overall air quality.
“I fear that when results come in from across all monitored speed limit changes, we will see Labour pushing the button on their road charging plans, as their only option to get commuters off the roads.”
Ruling politicians in Wales had brought in the blanket 20mph speed limit policy partly on the basis that lower speeds would improve air quality.
Vaughan Gething, the First Minister, previously told the Senedd: “Well, of course the 20’s Plenty campaign was predicated on an improvement to air quality and improvement to safety as well.”
His predecessor, Mark Drakeford, also said during a Senedd debate: “I don’t think there’s any doubt that the evidence demonstrates that [20mph limits] improve road safety and that they have a part to play in improving air quality and reducing carbon emissions”.
In the Welsh Government’s official study, carried out by scientists from civil engineering consultancy Jacobs, pairs of sensors were placed on roads that straddled the 20mph zone’s borders, with one pair being inside and one pair outside.
The idea was to obtain a like-for-like comparison about what the lower speeds meant for air quality.
Yet sensors picking up levels of nitrogen dioxide (NO2), a harmful gas emitted by petrol and diesel-engined vehicles, recorded differences inside and outside the 20mph zones that were statistically insignificant.
Scientists carrying out the study also had to abandon research into harmful particulates emitted by cars on the roads used for the study because “road traffic emissions on adjacent roads contributed very little to... [pollution] concentrations at each pair of sensors”.
The blanket speed limit reduction was imposed by Wales’ devolved Labour-controlled government in September.
An online petition against the reduction of speed limits from 30mph to 20mph became the most popular in the Senedd’s 25-year history, gaining nearly 470,000 signatures earlier this year.
Although Ken Skates, the new Welsh government transport minister appointed in April, said he would “correct” the blanket 20mph policy, the Welsh Tories have claimed this is a hollow promise.
Mr Skates said a month ago that councils would be given powers to raise speed limits again if they wished.
A Welsh Government spokesman said: “We have never claimed 20mph would make a material difference to air quality and to suggest otherwise is simply disingenuous.”
