31 Oct The problems of setting aircraft noise limits
Earlier this month, the World Health Organisation (WHO) published its long-awaited Environmental Noise Guidelines for the European Region. In it, the recommended maximum annual average level for aircraft noise is lower than for other modes of transport, lower than current EU policy, and lower than currently in effect at nearly all European airports. So, before governments scramble to rewrite regulations – and airports to react to them – it is worth taking a closer look at the challenges of setting new limits.
The choices policy-makers will have to make are by no means cut and dried
Consequence of new noise limits
The WHO report includes, among others, recommendations for maximum aircraft noise levels that they find acceptable for public health. Based on studies and input from experts gathered between 1999 and 2015, they set their recommendation at a maximum of 45 dB Lden (40 dB Lnight). With these guidelines, the WHO strongly recommends that effective action be taken to reduce aircraft noise affecting the population above that level.
As we explained in our previous blog, with the majority of European airports currently working to thresholds of 55 dB Lden, it’s fair to say a reduction to 45 dB Lden would require huge changes to either airport operations or to existing land use across the entire continent. Naturally, then, the questions that arise for policy-makers are whether to adopt the WHO recommendations at face value, and how to deal with the consequences that adoption would imply. There are two critical aspects to be addressed when considering the WHO recommendations for aircraft noise.
Reliability of evidence?
The first question, of course, is the degree of reliability in the specific noise level and corrective measures presented in the guidelines. Is 45 dB Lden a reliable cut-off point above which public health is negatively affected, or is it more arbitrary than that?
One point that makes this question difficult to answer is the fact that the WHO’s strong recommendations themselves are derived from studies with weak to moderate quality of evidence. Furthermore, the evidence of interventions suggested also has a very low to moderate quality. Despite a rigorous methodology, it is difficult to see how low-quality evidence can support ‘strong’ recommendations.
Additionally, important studies such as the Survey of Noise Attitudes (SoNA) published in the UK in 2017 were not considered. The SoNA retested the UK’s previously defined level of 57 dB LAeq, 16h as the onset of significant community annoyance and found that this level now tends to start around 54 dB LAeq, 16h.
Furthermore, differences between noise levels indoors and outdoors were not considered for the WHO guidelines, nor were the effects of non-acoustic factors (psychological and cultural) on how noise is experienced.
Understanding of the impact
The second aspect is having a clear insight into the impact more stringent regulations would have on the current situation at airports across Europe. Around Amsterdam Airport Schiphol, for example, implementing the WHO recommendations would apply to more than 650,000 residences housing nearly 1.5 million people. Do you demolish 650,000 homes and rehouse 1.5 million people? Or should you close an airport serving millions of passengers and providing thousands of jobs and other economic advantages? The Netherlands is also one of relatively few examples of successful land-use planning around airports. The challenges for policy-makers may be much more difficult for other airports.
Multiple psychological and cultural variables also play a major role in the individual experience of noise nuisance. Some psychological factors with high impact can be managed, such as trust and attitudes toward the airport, or the general satisfaction with the area and how well homes are insulated. (Although, admittedly, misleading media headlines claiming some airport noise nuisance is actually 10 times higher than reported, based on the guidelines, make this much more difficult.) Other factors such as individual noise sensitivity and ability to cope and control the personal environment are impossible to address outside of closing airports or rehousing individuals. The choices policy-makers will need to make regarding the WHO recommendations are by no means cut and dried.
The WHO released its Environmental Noise Guidelines for the European Region on October 10th. You can download the executive summary here.
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