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Monitoring reveals better air quality near new 50mph limits

Air Quality

Rhodri Clark
14 October 2019

Air quality has improved at all locations in Wales where 50mph limits were imposed last year on trunk roads, although the mean traffic speed was significantly higher than 50mph.

The Welsh Government introduced the 50mph limits in June 2018 and made them permanent last summer. This week it published data from the first full year of operation.

By the A483 at Wrexham, the average roadside nitrogen dioxide concentration over the six months from December 2017 to June 2018 was 54.1μg/m3, using a national bias adjustment factor. The 12-month average to July 2019 was 44.2μg/m3, a reduction of 18 per cent.

By the A494 at Deeside, Flintshire, the reduction was from 43.6μg/m3 to 39.0μg/m3 (a 10.6 per cent reduction). By the A470 near Pontypridd, the reduction was from  60.4μg/m3 to 53.3μg/m3 (down 11.8 per cent) and at the M4 in Port Talbot from 52.2μg/m3 to 45.0μg/m3 (13.8 per cent less).

There was a smaller reduction where a 50mph limit for air quality was imposed on the M4 at Newport, from 64.0μg/m3 to 61.5μg/m3 (3.9 per cent). From May 2018, the 50mph limit operated overnight only. It has operated continuously since February.

The mean traffic speed was 58mph at Deeside and Pontypridd, 57mph at Wrexham and 55mph at Port Talbot. At Newport it was 53mph when the overnight 50mph limit was in place and 51mph from February onwards.

The 50mph limits at Port Talbot and Newport were, in effect, extensions of established safety-related 50mph limits on the adjoining sections of the M4.

The Welsh Government had hoped that publicity around the air quality issues would result in drivers complying with the speed limit out of consideration for residents. Around Christmas, it erected signs at the entry points to the 50mph sections to explain their purpose.

Average speed cameras – with green instead of yellow casings to denote environmental reasons – have now been installed at all of the sites except Newport (where spot speed cameras are in place), with a view to penalising drivers who ignore the 50mph limits. The Government’s report on the first year of operation says it expects that “compliance will be improved”.

It cautions: “The situation remains complicated as air quality is sensitive to a number of issues including the weather/seasonal effects, traffic flows including volume, speeds and fleet mix. Until additional information is obtained and the trends remain positive, it is too early to make firm conclusions or any other recommendations to remove the measures that have been either implemented or proposed at the five sites.”

Transport minister Ken Skates said: “I am encouraged by these findings in the first year of these speed limits, but it is vital we continue to reduce emissions in order to save people from the risk of developing potentially serious health conditions. I would hope most motorists would agree that helping to save people from illness or even death is more important than saving a minute or so on their journey.” 

Asked about the 50mph limit at Pontypridd in the Senedd last month, First Minister Mark Drakeford said: “We will do more over this autumn to put up information that explains to people why they are being asked to observe that 50mph speed limit.

“I think we’ve always been able to make an appeal to people in Wales to understand that collective effort has an impact on the lives of other people. We haven’t explained that well enough and persistently enough to people so far. I am optimistic that when we do that, we will see people observe that 50mph speed limit.”


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