I’m sorry, what did you say?

I was half-listening to HS2 Ltd’s expert witness on acoustics, Rupert Thornely-Taylor, drone on a few weeks back, presenting the HS2 Select Committee with the, now familiar, reasons for expressing the adverse effect thresholds, LOAEL and SOAEL, in terms of the equivalent continuous sound level, LAeq – in particular he claimed that there was “explicit guidance for what LOAEL [at night] should be, in the [World Health Organisation’s] night-noise guidelines for Europe” (see footnote 1). But in the midst of this well-rehearsed stuff he said something that really made my ears prick up.

Whilst describing the use of the LAeq index to average over the whole night period as “entirely valid and expressly recommended by the WHO guidelines” he opined “it’s most important to bear in mind that we also have Lmax criteria at night for LOAEL and SOAEL at night, and they are the dominating tests”. Just in case the Committee may have missed the significance of “and they are the dominating tests”, he added (see footnote 2):

“The Lmax requirements in Information Paper E20 are the most sensitive test. Actually, Leq at night, while it is an important part of the assessment process, is not the test which tells you how much mitigation is required in which areas. It is the Lmax which is the most important one.”

Now to be perfectly fair to Mr Thornely-Taylor, this was not, as I first suspected, a recent Damascene conversion. When I checked back, I found that he had said something similar when he first addressed the Committee on noise back in the summer of 2014. In explaining the “way lowest observed adverse effect level and significant observed averse effect level have been converted into numbers” he first of all identified that separate day and night LOAEL levels have been specified in terms of LAeq; but, he then added that “there is a secondary test at night, which is particularly relevant to a railway project”. He explained (see footnote 3):

“… what you get with a railway project is the passage of trains which in a quiet location will make more noise than the environment and the maximum level can be of more concern than the LAeq level”.

I have to confess, with some personal shame, that I missed the significance of this the first time around, so I am grateful for Mr Thornely-Taylor’s recent, rather more explicit, confirmation – I certainly didn’t miss it this time. I am pleased to say that, for once, I can wholeheartedly accept Mr Thornely-Taylor’s assessment, based upon evidence that has been presented to the Select Committee by two petitioners (see footnote 4).

The question that should be asked in the light of his acceptance of the primacy of LAmax in determining the LOAEL contour, is why HS2 Ltd has not grasped this concept wholeheartedly into its corporate bosom. If you look in the November 2013 version of the Phase 1 Environmental Statement (ES), for example, you will only find LOAEL specified in terms of LAeq (see footnote 5). You have to consult Information Paper E20 to find a reference to LOAEL expressed in the LAmax parameter.

The noise contour maps are also deficient in this respect; we have only been provided with these showing the LOAEL contour as specified by LAeq. On the basis of Mr Thornely-Taylor’s assessment and the LAmax maps that have been drawn by two petitioners that I refer to above, the LAeq maps are likely to understate the extent of the area that is above LOAEL. This understatement extends to the evidence given by the Promoter to the Select Committee, where the situation with respect to LOAEL of the home of the petitioner being heard  has habitually been expressed solely by reference to the LAeq contour, even when the LAmax level quoted in the ES Volume 5 tables has also been advised.

The “official explanation” of why we are expected to endure this totally-confusing situation was given to me by Mr Thornely-Taylor when I asked him about it when my petition was heard back in January this year. He said (see footnote 6):

“The LOAEL concept does not have a place in Environmental Assessment Regulations. The requirement is to assess significant effects and LOAEL is an order of magnitude less.”

In other words, rather than provide all of the information that a resident may need in the ES, HS2 Ltd is hiding behind a deficiency in the Environmental Assessment Regulations to withhold from the ES the full assessment of the LOAEL situation of receptors that is necessary to satisfy the requirements of the Noise Policy Statement for England.

My own theory of why HS2 Ltd would want to be this obtuse, other than the usual highhandedness, is that E20 post-dates the ES, and that expressing LOAEL using LAmax was only agreed subsequent to the ES being published – but perhaps I am being too cynical and I should take Mr Thornely-Taylor at face value. After all, if my theory why the 2013 version of the ES makes no reference to the LAmax LOAEL is correct, you would have thought that the publishing of the Supplementary Environmental Statement in July 2015 would have been the opportunity to correct the omission, but this didn’t happen.

What isn’t totally clear, as a result of this confusion, is whether the assessment of receptors above LOAEL that has been carried out by HS2 Ltd, and it follows the evaluation of the need for sound mitigation measures, has been based upon LAmax rather than the apparently less-rigorous LAeq.

I’m not sure how to get to the bottom of this, but would strongly urge those petitioners still to be heard by the Select Committee to contest any assessment of sound impacts that relies on the LAeq contour maps alone. Also, when using LAmax to assess LOAEL don’t forget to add 2.5dB(A) to the figures that have been calculated by HS2 Ltd as I explain in my blog Facing a brick wall, part 2 (posted 1 Oct 2015).


  1. Mr Thornely-Taylor was giving evidence during the afternoon session of the HS2 Select Committee held on Monday 12thOctober 2015. His evidence is recorded from paragraph 229 in the transcript and from 15:45 hrs in the video.
  2. See paragraphs 233 and 234 in the transcript of the afternoon session of the HS2 Select Committee that was held on Monday 12thOctober 2015.
  3. See paragraph 62 in the transcript of the morning session of the HS2 Select Committee that was held on Tuesday 8thJuly 2014.
  4. These two witnesses both showed the Committee maps that they had drawn for the respective locations they were representing that showed that the 60dB LpAF,Max contour enclosed a significantly larger area than the 40dB LpAeq,night The witnesses were Cllr Andrew Burrow on the morning of Wednesday 10thDecember 2014 and Mr Steve Summers on the afternoon of Tuesday 14th July 2015. For further details please refer to my blog A very noisy bird, part 1 (posted 22 Aug 2015).
  5. Refer, for example, to paragraph 1.5.44 of Annex A to ES Appendix SV-001-000.
  6. See paragraph 98 in the transcript of the morning session of the HS2 Select Committee that was held on Wednesday 21stJanuary 2015.

PS: Subsequent to me writing this blog, Mr Thornely-Taylor has made what could be regarded as an even more emphatic statement of the dominance of the LAmax threshold for LOAEL. He told the Select Committee on the afternoon of Wednesday 4th November 2015 that “the geographic extent of the requirements that come with being above LOAEL is actually much greater [using LAmax] than the 50 LAeq on the map”. He also acknowledged “that the figure of 60 LAMax is a free field trigger, equivalent to 63 in front of a façade” (see paragraph 12 of the transcript).

Important Note: The record of the proceedings of the HS2 Select Committee from which some of the quotes reproduced in this blog have been taken are uncorrected transcripts of evidence, which are not yet an approved formal record. Neither witnesses nor Members have had the opportunity to correct the record in such instances, and it may therefore be subject to changes being made in the light of any such corrections being requested.



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