Innovative strategies and challenges in mitigating road traffic emissions
There is limited evidence of effective mitigation for air quality impacts from road traffic emissions on internationally protected sites. Attempts from environmental professionals across the industry have included the use of speed limits, pollution barriers, and tree shelter belts; however, these techniques may have conflicting outcomes, and their efficacy can be difficult to quantify. Furthermore, case law has demonstrated the difficulties in applying other approaches for the purposes of mitigation for sites protected under the 'Habitats Regulations'. As a result, road developments with air quality impacts have faced significant challenges to consenting.
Trailblazing solutions to combat road traffic pollution
Our team developed an alternative, legally compliant approach that targets other sources of nitrogen emissions to negate the air quality impacts of road traffic. The team identified that modifying agricultural activity on land close to a protected habitat site would result in a reduction in airborne ammonia concentrations. This would, in turn, reduce the rate of nitrogen deposition as evidenced through dispersion modelling of agricultural emissions. This allowed the reduction in nitrogen deposition across the protected habitat site to be calculated. The model considered information on agricultural activity from landowners and activity-specific emission rates provided by the National Atmospheric Emissions Inventory.
Pioneering legal compliance in environmental assessment
The approach has been published in the industry-leading Habitats Regulations Assessment Journal in January 2024 and was presented at the UK CAPER (Committee on Air Pollution Effects Research) 2024 conference. Since its incorporation within the consent applications for two large infrastructure projects delivered by WSP in the UK, our team worked with the Statutory Nature Conservation Bodies (Natural England and NIEA in Northern Ireland), with support from leading environmental law firm, Freeths, to demonstrate that the approach was legally compliant. NWRR was recognised by Natural England's High Risk Case Work Panel as being the first case in the UK to deliver the approach.
Collaboration to enhance environmental and social value
In addition to air quality mitigation, the approach for NWRR was expanded in collaboration with the Water Discipline to assess the additional mitigation that could be achieved at designated sites through reducing nutrients via aquatic pathways. Consent for the NWRR was granted in 2024. Post-consent of NWRR, the team continues to work with our client, Shropshire Council, to maximise opportunities to support additional scientific research and added social value through monitoring and research proposals.
Highlights from the project
- 32km: Length of the new underground pipeline.
- Cross-border project: Spanning North West England and North Wales.
- Multiple stakeholders: Including Natural England, Natural Resources Wales, Cheshire West and Chester Council, and Flintshire County Council.
- Novel survey methodology: Developed for assessing impacts on foraging and commuting bats.
- Biodiversity Net Gain: Commitment to achieving gains in Habitats of Principal Importance.
- The CAPER conference: Demonstrated significant information dissemination across the industry, with Hencott Pool figures showing air quality impacts and mitigation achieved across the whole site.
