How we're tackling air quality
A look at the various measures and initiatives we're undertaking to improve air quality on and around our roads.
Environmental Sustainability Strategy and New Zero Plan
Assessment reports and ongoing evaluation
Our Environmental Sustainability Strategy and Net Zero Plan
Our Environmental Sustainability Strategy presents our roadmap to an environmentally sustainable strategic road network including our ambition to mitigate air pollution.
Our Net Zero Plan details our progress towards reducing emissions from maintenance and construction activities, as well as road user emissions, to support transport decarbonisation with associated air quality benefits.
Measuring air quality
To help us understand air quality alongside our roads we use a number of different sources of data and information, including two types of air quality monitoring.
Automatic monitors allow us to collect data in near real time but have limitations including space for the monitoring station and availability of a power supply.
Diffusion tubes are small, easy to install to existing street furniture like lampposts and they don’t require power. They can’t provide real-time information like the automatic monitors and instead report monthly averages. But we can use the measurements to compare against the legal limits.
Over the last 10 years we've established a network of approximately 60 automatic monitoring stations. These monitors continuously gather real-time data on concentrations of nitrogen dioxide (NO2) and particulate matter at these monitoring stations.
To complement our automatic monitoring stations, we also regularly deploy diffusion tubes to measure concentrations of NO2. Diffusion tubes can be installed on lampposts and other street furniture across areas of potentially poor air quality, helping to define the extent of the affected area.
Together, this monitoring provides data allowing us to understand air quality across our network and how it's changing over time. This also helps us to focus on areas of poor air quality and monitor the effectiveness of any measures to improve air quality.
View National Highways Air Quality Monitoring Network (NHAQMN) reports
Research and innovation
We've led one of the largest programmes of air quality research over the last 15 years. Our programme of research has had a far-reaching scope, looking for new and innovative ideas, to help improve air quality so that we can protect local communities and ecological sites.
Historically, the focus of our research has been trying to find solutions to reduce the concentrations of nitrogen dioxide (NO2) and their impacts on human health. More recently we've expanded our research programme to look at the impact poor air quality is making to ecological sites and what we can do to minimise these impacts.
We've produced a research compendium which summarises the findings from all of our research. The more detailed research reports which provide the different pieces of work we’ve undertaken are available from our research publications.
Types of intervention
Over the last five years we've deployed a range of measures around the country to help improve air quality at locations on our network including:
- 60mph speed limits to help reduce emissions from cars and vans
- working to accelerate the uptake of zero emission vans
- closing public access
We’ve either removed or are in the process of removing the 60mph speed limits as air quality is now below the legal threshold on the five of sections of network where we’d previously installed them. As part of running the 60mph air quality speed limits, we’ve also investigated how well they performed. The reports can be found in the speed limit trials section of our air quality library.
A3 footpath closure
We're working with Surrey County Council and Guildford Borough Council to find ways to reduce the impact of poor air quality alongside the A3 in Guildford.
This is part of a wider piece of work we're doing to track roadside nitrogen dioxide concentrations where they're above the annual mean legal limit of 40μg/m3.
We've conducted a thorough review of potential options, including large scale interventions such as barriers.
These proposals aim to direct people away from areas of poor air quality to upgraded alternative routes.
Find out more about our A3 Guildford air quality project
A282 cycle shelter relocation
We relocated the cycle shelter alongside the A282 from an area of high NO2 concentrations to an area with lower NO2 concentrations to protect cyclists from poor air quality.
Speed limit trials
We’ve either removed or are in the process of removing the 60mph speed limits as air quality is now below the legal threshold on the five of sections of network where we’d previously installed them.
M5 junction 1 to 2 Oldbury is the only location with a speed limit remaining in place. The 60mph speed limit will remain in place while we work through the legal process needed to remove the 60mph speed limit. In the meantime road users will need to keep driving to the displayed speed limits.
As part of running the 60mph air quality speed limits, we’ve also investigated how well they performed. The reports can be found in our air quality library.
Assessment reports and ongoing evaluation
We've always taken a rigorous, evidence-led approach to assessing and implementing measures to improve air quality. We're committed to being transparent about our work and publish comprehensive information in our library.
Developing our air quality programme has required a lot of investigation, monitoring and modelling. Our publications include all the assessment reports and supporting information. We’ve also undertaken extensive air quality assessments for different parts of our network.
We're continuing to watch the remaining areas of our network identified above legal thresholds. Each year we produce a progress report on the state of air quality in those areas and any actions that we've been able to take to try and improve the situation.
To help find all of our current monitoring, we've created a map which shows all of our monitoring sites and the measured concentrations.
Ongoing evaluation
To make sure that we continue we do all we can and are also able to remove any measures when we no longer require them, we undertake a review once a year on the state of air quality alongside our network previously identified above the legal threshold. These are all available in the Annual evaluation reports section of our library and you can look up air quality in your area on our interactive map.
With air quality continuing to improve across the country we expect fewer areas to require action in future, although we'll continue monitoring alongside our network for any new areas of poor air quality.
Pollution Climate Mapping link evaluation strategy
Following the agreement with the Joint Air Quality Unit, a number of links have been identified as above the permissible levels.
We've developed an evaluation strategy to:
- understand and report when each link is compliant
- determine whether any mitigation is delivering the improvements
- confirm when any mitigation can be removed while ensuring the section of the Strategic Road Network (SRN) remains compliant
Evaluation approach
Air quality monitoring will be deployed for all links confirmed as non-compliant and assessed within 10% of the limit value, i.e. 36-40µg/m³.
Monitoring will be deployed to at least one site as a minimum, but ideally three, alongside the SRN representative of qualifying feature(s).
Monitoring will continue for at least two years after the respective section of the SRN is modelled to come into compliance.
Monitored concentrations will be evaluated at six-month intervals, (allowing two months for tube analysis by the labs):
- mid-year review – end August year – covering first six months
- annual review and report – end February year – calendar year annual average
Removing mitigation will be recommended when concentrations are reported below 36µg/m³.
Annual Evaluation report 2024 (published July 2025)
Our Air Quality Annual Evaluation Report for 2024, published in our Annual Report and Accounts 2025, continues to show ongoing improvements in measured NO2 concentrations, continuing the trend seen since the end of the pandemic.
The ongoing improvements in air quality mean that many of the sections of our network that we've been asked to assess over recent years are now well below the annual mean NO2 limit value of 40μg/m³. Over the last 12 months we've confirmed that the limit value has been met on a further 27 links.
| Limit value status | Number of links - Annual Evaluation Report 2023 | Number of links - Annual Evaluation Report 2024 |
|---|---|---|
| Above | 20 | 15 |
| Within 10% | 14 | 11 |
| Total | 34 | 26 |
Our Annual Evaluation Report 2024 has identified that 15 sections of our network are above the limit value, including three new links. We're exploring the measures available to us, such as footpath closures, barriers or local traffic management measures, to see if we can address these remaining areas of poor air quality.
Get in touch
If you have something you’d like to discuss with us, please get in touch by emailing: airquality@nationalhighways.co.uk
