Unsound Measurements

10/11/13

 By John Stewart

They won’t know whether to laugh or cry this weekend, the residents of Sabine Roadin Battersea.  Their street has been named one of the quietest in London“Sorry you did say ‘quietest’ didn’t you?”  They’ll be asking each other over breakfast as the next plane roars overhead.

Sabine Road, not far from Clapham Junction, is in an area where there have been countless complaints about aircraft noise the years.  It’s on the flight path to Heathrow.

So what is going on?

The researchers, from the noise consultancy firm 24 Acoustics have fallen into the classic trap of using the official UK method of measuring aircraft noise. 

“To determine the quietest streets, researchers used existing data to locate which ones were outside of the 57 decibel noise contours for airports, and had a night road traffic noise level of lower than 35 decibels”

This reliance on the 57 decibel noise contour has made a mockery of their results.  It has meant that aircraft noise can be heard in just about all their top quietest streets.  Streets in places like Fulham and Putney make it into the top 10.http://www.standard.co.uk/news/london/silent-nights-the-capitals-10-top-quietest-streets-revealed-8928506.html

The blame lies not with the researchers.  I imagine that in good faith they accepted the official measurement of noise annoyance from aircraft.  It was a mistake waiting to happen.  For years HACAN, along with many other bodies, has argued the measurement is utterly misleading.

We wrote in our response to the Airport Commission’s consultation on noise:

“The current 57 db Leq contour – the official area which defines where community annoyance sets in – excludes places like Putney and Fulham in West London!  Not the real world!”

The European Commission agrees with us.  It requires member states to use a different metric – called 55Len – when drawing up their noise maps.  That is more realistic.  It extends the noise boundaries to places like Vauxhall and Clapham.  But even it does not cover all the places where people are annoyed.  The ANASE Study, commissioned by the last Government but quietly buried when it found the findings were not to its taste, found that there is significance noise annoyance well beyond the 55Lden contour.

Of course the current 57 decibel cut-off point suits the aviation industry down to the ground because it minimises and underestimates the numbers affected by noise.

However, here are distinct signs the tide is turning.  Sir Howard Davies, who heads up the Airports Commission, is known to be looking seriously at a more realistic metric.

In their responses to the Commission’s noise paper, MPs queued up to criticise the current cut-off point: https://www.gov.uk/government/publications/stakeholder-responses-to-airports-commission-discussion-papers

 Mary Macleod MP: “There is widespread evidence that the existing measure of the threshold of annoyance is inaccurate and misleading.”

Zac Goldsmith MP“The measurement of noise – and of noise annoyance/disturbance – needs revising. Currently it is misleading.  Any noise measurement that does not reflect reality lacks credibility”.

Former Transport Secretary Justine Greening MP: “I believe this strongly shows that taking a traditional 57dB approach to assessing the level of noise annoyance from any new aviation strategy will exclude a large number of people who will be annoyed and affected but live outside of the 57dB noise contours.”

John Randall MP: “Clearly, a 57dB threshold is unhelpful if it excludes population areas that are experiencing significant annoyance from aviation noise”.

Murad Qureshi for the London Assembly Labour Group: “The committee has previously recommended the adoption of an Lden measure and the use of lower thresholds for identifying the areas most affected by aircraft noise”.

 Boris Johnson, the Mayor of London:   “The development of a new noise metric is strongly supported. It must fully represent sensitivity to and the impacts of aviation noise and how individual aircraft events are experienced during different times of day and night”.

 Even the Government in its Aviation Policy Framework, published in March, recognised the current measurement was flawed:

“Average noise exposure contours are a well-established measure of annoyance and are important to show historic trends in total noise around airports. However, the Government recognises that people do not experience noise in an averaged manner and that the value of the LAeq indicator does not necessarily reflect all aspects of the perception of aircraft noise. For this reason we recommend that average noise contours should not be the only measure used when airports seek to explain how locations under flight paths are affected by aircraft noise.”

The Airports Commission has been charged with reassessing the way aircraft noise is measured.  A change to a more realistic noise metric could be the most lasting    decision it will make.  It will ensure that future aviation policy decisions are based on sound measurements.

And it will save future researchers falling into the same trap that ensnared the benighted people from 24 Acoustics.

 

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