Cumulative air quality impacts: lack of clarity leaves room for confusion

Cumulative air quality impacts: lack of clarity leaves room for confusion

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Fiona Prismall, Technical Director, discusses the implications of the Wealden case and the questions it raises for the assessment of cumulative air quality impacts on nature conservation sites.

The effect of air pollution on human health in our towns and cities has now begun to be recognised by the general public and in the media. Much less well publicised, however, is the effect air pollution can have on flora and fauna in sensitive ecosystems.

In March 2017, Wealden District Council won an important High Court case against the Secretary of State for Local Government, Lewes District Council, the South Downs National Park Authority and Natural England. The case concerned air quality impacts on Ashdown Forest, a sensitive habitat that has been designated a Special Area of Conservation (SAC), wholly located within Wealden and approximately 5 km from the boundary with the district of Lewes.

The districts of Wealden and Lewes both contain parts of the South Downs National Park. Wealden and Lewes each developed a Joint Core Strategy (JCS) with the National Park Authority; both of which contained proposals for housing development likely to generate traffic on the A26, running alongside the Ashdown Forest SAC. The impact this new traffic movement would have on the air quality was therefore an important consideration.

Natural England (NE) advised both councils that if the estimated annual average daily traffic flow was less than 1000, they could conclude no likely significant effect on the SAC. Wealden estimated that its housing allocations would on average generate 950 daily traffic movements on the A26. Lewes estimated 190. As each was below 1000, both parties concluded that there would be no likely significant effect on the SAC either alone or in combination. The Wealden JCS was adopted in February 2013 and the Lewes JCS was adopted in June 2016.

However, in August 2016, Wealden challenged the adoption of the Lewes JCS. Wealden claimed that Lewes should have added Wealden’s 950 daily traffic movements to their own figure of 190 before concluding no likely significant impact on the SAC. This would have meant a combined total of 1140 daily traffic movements – above the 1000 threshold.

During the court hearing, Lewes’ counsel pointed out that Wealden had relied on the same advice from Natural England; however, the High Court found in favour of Wealden. The court stated that Natural England had given Lewes Council erroneous advice in allowing them to conclude no likely significant effect for the 190 daily traffic movements without taking into account Wealden’s 950. Effectively, Wealden had been successful in its claim by virtue of the fact that it had adopted its JCS first.

It is important to note that the 1000 daily traffic threshold is drawn from Highways England’s Design Manual for Roads and Bridges (DMRB), the purpose of which is to provide guidance for the assessment of road schemes, rather than local plans and/or individual projects. While the DMRB doesn’t specifically state that the threshold applies both alone and in combination, it is understood that this is the case based on the low risk of a number of road schemes coming forward and affecting a single nature conservation site.

While the Wealden case applies to the development of local plans, the outcome of this case is more far reaching and is already raising issues in relation to the approach to the scoping assessments for individual projects where there is the potential for cumulative impacts.

In my view, this is a difficult issue to resolve and we need organisations such as Highways England, Natural England and the Environment Agency to make their positions clear. Without understanding those positions, air quality consultants, transport consultants and ecologists will be left to decide the extents of studies in terms of which developments should be included in assessments and which should not. Clearly, different consultants might well come to a different conclusion for the same development.

The High Court ruling in the Wealden case suggests that there is still a case for thresholds, stating that impacts which are ‘very low indeed… can properly be ignored’. The example quoted during the case was that there would need to be 50 developments, each generating 20 daily traffic movements for the 1000 daily traffic threshold to be exceeded. Life is never that simple though. It is more often the case, that there are a large number of small developments along with one or two major developments. Are we being advised to ignore the sum total of those small developments and focus on the impacts of the larger developments only or, in so doing, could we fall foul of the same judgment that has been found against Lewes?

A further question is whether the ‘other’ developments to be considered should only be those that are already consented or should it include proposed developments that have not yet been determined?

While we wait for Highways England, Natural England and the Environment Agency to make their positions clear, all we can do as consultants is to be as rigorous as we can be in determining which other plans and projects are likely to impact on a nature conservation site and be completely transparent in the conclusions that we draw.