Natural England’s advice in regard to assessing in-combination effects on air quality has been found to be erroneous.

The outcome of a high court challenge to the approach taken by Lewes District Council and the South Downs National Park Authority when developing their joint core strategy (JCS) is likely to have significant implications for assessment of air pollution effects on European designated sites under the Habitats Regulations.

Specifically Mr Justice Jay ruled that Natural England’s current advice on the approach to in-combination effects of increasing traffic emissions resulting from new developments is erroneous and must be reconsidered (more more details can be found here).

The current guidance set out in the Design Manual for Roads and Bridges (DMRB) has been interpreted by Natural England as meaning that any plan or project where predicted traffic increases along sensitive sections of road are below a threshold of 1000 annual average daily traffic (AADT) can be scoped out and do not require further consideration of in-combination effects. This approach was taken in relation to assessment of Ashdown Forest Special Area of Conservation (SAC) by Lewes District Council and South Downs National Park Authority when developing their JCS. As the JCS would generate increases in traffic below the 1000 AADT threshold along roads adjacent to the SAC, impacts on Ashdown Forest were scoped out of further consideration under the Habitats Regulations.

Mr Justice Jay, however, ruled that Natural England’s expert advice on this matter “cannot be supported on logical and empirical grounds”, and Lewes District and South Downs National Park Authority should have taken into account the traffic generated by Wealden District Council’s core strategy, which in-combination, would exceed the 1000 AADT threshold. Mr Justice Jay went further to state that “Natural England must reconsider its advice in the light of this judgement” and “the DMRB should be re-examined, and clarified, to reflect the concerns I have indicated.”

The implications of this decision are that in-combination increases in traffic must be considered when scoping a plan or project for impacts on a European site under the Habitats Regulations, even where the plan or project individually does not exceed the 1000 AADT threshold along sensitive roads. Given a plan or project may result in an increase in traffic some distance away, this has the potential to affect proposed developments across a wide area.

This judgement follows Wealden District Council’s adoption of a temporary embargo on any planning consents resulting in increased nitrogen deposition along roads within or adjacent to Ashdown Forest SAC, following recent monitoring which has indicated that any further increase would have significant effects on the SAC. Further detail is provided here.