Speed Limits Due To Air Quality
Case reference EIR2024/00183
Received 1 June 2024
Published 6 September 2024
Request
Response
I can confirm that we hold the information you have requested.
Who approved the 60mph speed limit trials including the M4 Jn3-4?
The Department for Transport approved the speed limit trials.
The scientific level of air quality requiring the 60mph speed limit for air quality
The annual mean nitrogen dioxide (NO2) limit value of 40μg/m³, as set out in Schedule 2 of the Air Quality Standard Regulations (2010).
How many days in 2024 this restriction was actioned?
The limit value is calculated as the average of all hours in a year (8760 or 8784 for leap years), therefore the 60mph speed limit for air quality is displayed at all times.
The only times the message for air quality is not displayed is where there is a need to display an alternative message and / or lower speed limit. For example in the case of congestion or a lane closure.
Documents
This is National Highways' response to a freedom of information (FOI) or environmental information regulations (EIR) request.
You can browse our other responses or make a new FOI request.