Gladiatorial games, part 4

(… continued from Gladiatorial games, part 3, posted on 30 Nov 2015).

It emerged from the evidence given to the HS2 Select Committee by Rick Methold, expert witness on acoustics for Chiltern District Council (CDC), early in November (see footnote 1) that there is one crucial area where it appears highly unlikely that an accommodation with HS2 Ltd will be achieved, and this occupied the greater part of the day’s proceedings. The matter in dispute is the appropriate level of equivalent continuous sound level computed over the sixteen day hours of 07:00 to 23:00, designated LpAeq,16hr, that should represent the lowest observed adverse effect level, LOAEL.

The acronym “LOAEL” will be, by now, very familiar to anyone who has taken part in or watched the proceedings in Committee Room 5; scarcely a session has passed where it has not been mentioned by someone in the room, and it is typically referred to many times per sitting. You will probably be aware in addition that an equivalent continuous sound level value of LOAEL has also been set for the night hours of 23:00 to 07:00 and that a second LOAEL threshold also operates at night determined by the train pass-by maximum sound level, LpAFmax. However, Mr Methold’s evidence was concentrated upon the value of the threshold chosen by HS2 Ltd for the daytime LOAEL and its application, so I will do the same.

It may be helpful, before considering Mr Methold’s submission, to review the way that daytime operational airborne noise effects have been assessed in the Environmental Statement (ES).

The daytime LOAEL threshold value specified in Information Paper E20 Control of airborne noise from altered roads and the operational railway is 50dB LpAeq,16hr free-field (see footnote 2) and that is the value that has been utilised for the purposes of the ES.

The application of this threshold in the ES that affected residents will probably be most familiar with is the SV-05 series of noise contour maps in the Volume 2 map books. Whilst these maps are actually drawn to show the area encompassed by the night LOAEL equivalent continuous sound level threshold, the 40dB night contour has been assumed to be coincident with the 50dB day contour; the justification for this simplification is stated to be that the “extent of the 40dB night-time sound level contour is equivalent to, or slightly larger than, the 50dB daytime contour” (see footnote 3).

However, these maps do not show the complete picture and so should be treated with caution. They only take into account the noise generated by passing HS2 trains and ignore the important noise contribution in some locations arising from the realignment and other alterations of existing roads that is required to construct HS2 (see footnote 4).

This is a shortcoming that was brought home to me when I questioned the predicted night LpAeq for the road where I live, which at 43dB LpAeq,8hr is 3dB(A) above LOAEL night despite my home being located well outside the LOAEL contour on the map in the ES. I was told by the Promoter “that it is the [change in] traffic noise that gives rise principally to the noise levels” – Rupert Thornely-Taylor ventured that, from memory, the railway contribution to the HS2 noise figure was “about 37[dB(A)]” (see footnote 5).

In order to get a more meaningful picture of the likely adverse effects of HS2 noise it is necessary to consult the Operational airborne sound level, noise impacts and effects tables that are provided in the ES (see footnote 6). In these tables, the impacts predicted for the “Proposed Scheme”, in terms of the LpAeq levels quoted, include traffic noise increases, where appropriate. It is important to note, however, that the processes employed to construct the tables apply a further test to identify adverse impacts, which relates to the impact criteria defined in Table 7 on page 27 of ES Volume 5 Appendix SV-001-000. This test requires that HS2 noise should be sufficient to cause the ambient noise to increase by at least 3dB(A), corresponding to a “minor” long-term impact classification in Table 7, in addition to exceeding the LOAEL threshold.

In his evidence Mr Methold provided illustrations of how these criteria are applied in the ES, speaking to his exhibit A1571(25) which is one of the pages of the Operational airborne sound level, noise impacts and effects table for CFA10 (see footnote 7). I will follow his lead and point to three examples in the table that illustrate how adverse effects have been identified, or not, using these criteria.

In the top row of the table, relating to North Lee Lane Terrick (ID312373) the “Proposed Scheme only” day noise LpAeq is shown as 51dB(A) and the resulting ambient noise level change as 3dB(A). The former, being above the LOAEL threshold, gains the location an “A” in the “Type of effect” column, confirming that there is an “adverse effect”, and the latter a yellow background colour rating it as a “minor impact” as per Table 7 in SV-001-000.

Nash Lee Farm (ID314625) in the tenth row of the table is also predicted to experience HS2 noise above LOAEL day, at 52dB(A), and is also marked “A” as a result, but at this location the ambient noise change is only 2dB(A), which is rated as a “negligible” impact. The result of this impact rating is that the location is deemed as not meriting any further consideration.

My final example is North Lee Lane Terrick (ID313140), which is the fifth row of the table. Here the daytime ambient noise change is predicted to be 5dB(A), which would merit a “moderate” impact grading and an orange background colour, but the predicted HS2 day noise level is, at 49dB(A), below the LOAEL threshold, so the location is assessed as having a “NA” (no adverse effect) grading and will receive no further consideration.

Even locations such as ID312373 that survive this sifting process have a further hurdle to clear, which is whether the effect is “significant on a community basis”, but I will look at that in the next part.

Mr Methold’s evidence indicated that the LANC has a number of issues with the principles that underlie the procedures that I have outlined above, and I will explain the what and why of these objections as this series of blog unfolds.

(To be continued …)


  1. The evidence presented on behalf of CDC occupied the whole of the morning session of the HS2 Select Committee that was held on Wednesday 4thNovember 2015 (video) and the Promoter’s response was given in a shorter than usual afternoon session (video).
  2. See Table 1 in Appendix B of Information Paper E20.
  3. See paragraph 8.9.28 of Volume 1 of the ES. For this assumption to be valid, the calculated values of LpAeq for the day hours at every location should be no greater than 10dB(A) above the equivalent for the night hours. A check of the predictions listed in Table 3 of ES Volume 5 Appendix SV-004-010 confirms that the day to night margin at all of the identified receptors lies within the range 7 to 10 dB(A).
  4. This is confirmed in the legend box on every SV-05 map, which refers to “HS2 (rail only) sound level”. Basing these maps on the LpAeq values is also questionable bearing in mind that, as I reported in my blog I’m sorry, what did you say? (posted 14 Nov 2015), it is common ground between some petitioners and the Promoter’s acoustics expert that “the geographic extent of the requirements that come with being above LOAEL is actually much greater” when the LAmax value of the LOAEL night threshold is employed rather than LpAeq.
  5. See paragraphs 53 and 54 of the transcript of the morning session of the HS2 Select Committee that was held on Wednesday 21stJanuary 2015.
  6. These may be found in the series of appendices to Volume 5 SV-004.
  7. See paragraph 157, and following paragraphs, of the transcript of the morning session of the HS2 Select Committee that was held on Wednesday 4thNovember 2015. Note that the transcript is in error in attributing the words recorded in paragraphs 157 and 158 as being spoken by Mr Lewis, rather than Mr Methold as was the case.


I wish to thank Michael Woodhouse for his suggestions and comments, which I have found invaluable in preparing this series of blogs.

Exhibit A1571(25) has been extracted from the bundle of evidence submitted to the HS2 Select Committee by Rick Methold and published on the website of the HS2 Select Committee.

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 is an uncorrected transcript of evidence, which is 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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