The councils also said that the government would now have to produce figures showing the true scale of the noise impact.
Tough new Heathrow conditions make runway unbuildable
The Transport Select Committee criticised the way the Department for Transport had understated the numbers of people likely to be affected by noise - writes hillingdon.gov.uk
The MPs concluded that 'the approach taken has resulted in an analysis that tends towards the lower end of the range of possible noise impacts.'
The MPs said the government should not try to reduce the apparent impact by netting off the winners and losers among people experiencing noise. They noted evidence suggesting that over 300,000 could be newly affected by significant levels of noise annoyance.
They found that the government had not followed its own guidance in setting the threshold for annoyance - applying a higher level (54dB) than that recommended (51dB).
They also criticised the use of a single flight path scenario when in practice a variety of approaches would be used. These could increase the numbers of people affected.
The MPs concluded that that the evidence showed a third runway could have a 'seriously damaging effect on communities living under and adjacent to flightpaths.'
They added that without actual flightpaths it was 'impossible' to know what the exact noise outcomes would be.
They called on the government to update their noise modelling by using a variety of metrics and to define what they mean by 'significant adverse impacts'. The government should also define an acceptable number of people newly exposed to noise due to the scheme.
Cllr Simon Dudley, Leader of the Royal Borough of Windsor and Maidenhead Council, said: "Until now it has suited the Transport Department to keep people in the dark on noise and play down the numbers.
"Now for the first time the Department will have to publish the true scale of the noise impact for people affected by Heathrow expansion. This will be guaranteed to generate unprecedented levels of opposition to the scheme throughout London and the Home Counties."
Transport Secretary Chris Grayling previously claimed in October 2016 that an expanded Heathrow would be quieter in 2030 than today.
The revised draft consultation on the airports national policy statement (NPS) published in October 2017 predicted that 92,700 additional people in the area around Heathrow would be exposed to noise by 2030 as a consequence of the third runway.
The councils believe that the new noise metrics required by the Select Committee will show at least 2mpeople experiencing greater noise.
On air quality the committee said the proposed runway was at high risk of breaching legal levels between 2026 and 2029. They noted that the government's own air quality plan had been found unlawful on three occasions.
They said 'this did not fill us with confidence that its current plan can be delivered effectively to ensure the runway is capable of taking place within legal limits.'
The Committee underlined the importance of the health impacts of increases in pollution and recommended an additional condition that development consent would only be granted if it avoids significant adverse impacts on health and quality of life from poor air quality.
The MPs concluded by calling for the government to adopt a more stringent approach to air quality compliance and to include an appropriate level of headroom to manage the inherent uncertainty of predicting future compliance.
On the road traffic implications the committee recommended that planning approval should only be granted if the target for no more airport-related traffic can be met.
Cllr Ray Puddifoot, Leader of Hillingdon Council, said: "The councils have pointed out repeatedly the very high risk of a new runway breaching the legal air quality limits. The government has still offered no evidence showing how air quality obligations can be achieved.
'It is unthinkable that any government could allow a runway to go ahead which would damage the health of 121,000 people in the area.
"Expanding Heathrow would mean that not only would London continue to exceed legal limits it would also contribute to thousands of premature deaths up to 2030 and beyond."
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