Going over some old ground

In paragraph 6.3.49 on page 128 of its report High Speed Rail: Investing in Britain’s Future Consultation Summary Report (here) Dialogue by Design tells us that 799 respondents “argue that using averages instead of peak or pass-by noise levels is inappropriate”. Now this is quite a complex technical point and I was amazed to learn that so many people had picked up on it; they couldn’t all have been readers of my blogs.

This indicates to me that HS2 Ltd is making a mistake if it underestimates the intelligence of its critics. The response given in paragraph 7.2.7 on page 27 of Review of HS2 London to West Midlands Appraisal of Sustainability (here) indicates that it might be. Most of this paragraph is spent telling us what the equivalent continuous sound level, LAeq, is; I think that the 799 souls who raised this as an issue were probably already familiar with the concept, otherwise I doubt that they would have commented as they did.

We are also told in this paragraph that:

“In the UK and the EU, regulations, standards and policy all adopt this indicator to describe railway noise for both conventional and high speed lines.”


“The LAeq is the standard and most proven single indicator for determining noise impact of transport schemes and was therefore appropriate for the appraisal of HS2.”

These two sentences do little more than restate similar claims in section 1.2 on page 39 of Appendix 5.4 to the Appraisal of Sustainability Main Report (here).

Given the track record of HS2 Ltd, this is an entirely expected, but nonetheless disappointing, response. It is just not good enough. HS2 Ltd owes it to all those who will be affected by HS2 noise pollution to carry out a proper review of this issue to determine what are the most appropriate parameters to describe the impact of very high speed train noise accurately. This will be a new source of noise pollution and the reliance on the defence of using established parameters will not wash.

This is a very important issue because sole reliance on the single parameter LAeq,18hr to assess noise impacts carries a very great risk that these impacts will be understated and I intend to devote my next two blogs to explaining why I think this.

There are two further noise issues that have been raised in responses to the consultation, but are not mentioned in the Dialogue by Design report and we have to rely upon these being identified in Review of HS2 London to West Midlands Appraisal of Sustainability.

The first of these two issues is the 3 dB reduction in source noise level that has been assumed “based on the anticipated noise control improvements in the next generation of high speed rolling stock”; refer to paragraph 6.3.3 on page 50 in Appendix 5.4 to the Appraisal of Sustainability Main Report. No justification for this claimed noise level improvement was given in the Appraisal of Sustainability (AoS), but this is now provided by HS2 Ltd in its AoS review document (in paragraph 7.2.4 on pages 26 and 27). As I reported in my blog Perhaps you were right all along, perhaps not (posted 25 Nov 2011), the authority for this claimed noise reduction is an EU Commission Decision document and this is confirmed in the latest HS2 Ltd document (but see my PS, below).

In Perhaps you were right all along, perhaps not I gave reasons why the assumption of this 3 dB improvement is by no means a straightforward matter and I welcome the assurance in paragraph 7.2.4 of Review of HS2 London to West Midlands Appraisal of Sustainability that “the train noise level will be revisited and checked for suitability as the input to the more detailed EIA”. I trust that this work will be fully reported to the public in due course.

In this context I also trust that HS2 Ltd will similarly review whether an increase in source noise level should be made to allow for operational degradation in the track roughness, as suggested in my blog It could be a bumpy ride (posted 24 Oct 2011).

The second issue is the effective height of the train noise source compared to the proposed height of noise barriers and the resulting efficiency of the barriers. In Review of HS2 London to West Midlands Appraisal of Sustainability (in paragraph 7.2.5 on page 27) HS2 Ltd characterises this as “noise from the train pantograph”, although there are also other sources of aerodynamic noise high up on the train which may contribute. HS2 Ltd says in this paragraph:

“The pantograph is a consideration in the assessment of the noise impact and the AoS took this into account by making appropriate changes to the relative height of train source and barrier when considering mitigation. While noise from the pantograph does need to be considered, and will be reviewed at the time of the EIA, its significance is often overstated. The wheel-rail interface will remain the most significant part of the noise from the train, even at high speed.”

So we are, rightly, promised that this topic will be reviewed, and we are also told what the outcome of the review will be. Strange sort of review process, isn’t it?

I have already discussed this topic in my blogs A little bit of magic (posted 17 May 2011) and Going over the top (posted 9 Nov 2011), but I plan to research this potentially very important topic further and will report my findings in a future blog.

PS: The EU Commission Decision that allows the 3 dB reduction in source noise to be made is given as 2008/163/EC in footnote 24 on page 27 of Review of HS2 London to West Midlands Appraisal of Sustainability. Believing this to be an error, I queried it with the Department for Transport and have received confirmation that the correct EU Commission Decision is 2008/232/CE; this is the document that I quoted from in my blog Perhaps you were right all along, perhaps not.


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