What assessment has the Welsh Government made of the impact of the 50mph zones on air quality along the M4?
Air quality is monitored along the M4 at Newport between Junction 26 Malpas and Beaufort Road overbridge to the east of Junction 25, and at Port Talbot, between Junction 41 Baglan and Junction 42.
At both these locations 50mph speed limits have been introduced to support reductions in roadside nitrogen dioxide (NO2) concentrations and to achieve compliance with statutory limit values.
Since the reduced speed limits have been applied, reductions in NO2 concentrations have been recorded at both Newport and Port Talbot. Annual data, published in March 2020, recorded through diffusion tubes and adjusted using the national bias adjustment factor, confirmed a roadside annual average of 59.2µg/m3 (micrograms per cubic metre of air) at Newport in 2019. This was a reduction of 4.3µg/m3 from the previous calendar year. This reduced further to 38.4µg/m3 in the 2020 calendar year, which is below the statutory limit of 40µg/m3
At Port Talbot, annual average roadside concentrations were 43µg/m3 in 2019, a reduction of 5.4µg/m3 on the previous year. In 2020, concentrations reduced to 28.2µg/m3.