Getting a second opinion

Environmental aspects of the 51m consultation response, part 7

The 51m alliance employed Southdowns Environmental Consultants Ltd (Company website) to review the “assessment of high speed train noise impacts and proposals for mitigation presented in the technical appendix on noise and vibration” in the Appraisal of Sustainability (AoS). This company is well qualified to carry out this review, since its consultants played a significant role in the planning, assessment and delivery of HS1, providing technical input on noise and vibration aspects (more information on this involvement may be found on the Company’s website).

According to Southdowns “generic issues raised” by its review “include limitations in the scope, calculation, evaluation and mitigation of noise impacts adopted in the AoS”.

The result of the work by Southdowns is Appendix 18 to the 51m alliance response to the public consultation and input into the response to Question 6, which invited comments on the AoS (all sections of the 51m document may be downloaded from here).

Now I realise that it was only July when I hung up my ear defenders after rather a long stint on noise (The end of the line, posted 16 Jul), but you couldn’t expect me to let the opportunity pass of commenting on a professional review of the treatment of train noise in the AoS and to compare what the professionals have to say with my own comments.

So what I propose is to present in today’s blog a broad overview of what Southdowns has to say about the AoS and compare this with my own comments in my blogs in May, June and July of this year. In the next few blogs I will take a closer look at the views of Southdowns on specific noise topics.

So how does what Southdowns is saying stack up with the matters that I have raised in my blogs? The answer is quite closely. The following is a list of the issues which we have both highlighted:

  • In A little bit of magic (posted 17 May) I expressed doubts about whether three metre high acoustic barriers will be sufficient to shield trains producing noise from aerodynamic sources, and Southdowns has also expressed reservations about the way that the calculation of “acoustic benefits” from barriers has been made by HS2 Ltd.
  • Southdowns has reservations about the speed that has been employed for the calculation of noise levels in the AoS, and I also queried the use of 360 kph rather than 400 kph in “We don’t believe you” (posted 25 May).
  •  In “We don’t believe you” I also commented that no evidence had been offered in the AoS by HS2 Ltd to support its assumption that noise emissions from the next generation of high speed trains will be reduced by 3 dB due to “anticipated noise control improvements”, and Southdowns has commented that this assumption “requires further investigation and explanation”.
  • Southdowns expresses the view that “further research is needed” on whether the use of the equivalent continuous noise level over eighteen hours as the single noise indicator is an appropriate measure of noise nuisance, which was an issue that I raised in Taking a longer-term view (posted 22 Jun).
  • Southdowns doubts the suitability of the modifications made to the Calculation of Railway Noise 1995 model (CRN) to make it suitable for an aerodynamic noise source, and I have also queried this in Trust me, I’m an acoustic engineer (posted 4 Jul).
  • Southdowns has commented on the absence of any consideration of night-time noise nuisance, as I did in It’s on the level (posted 8 Jul).

The Southdowns report adds important insights to these topics and I will cover this aspect further in future blogs.

Three matters that I have raised are not included in the Southdowns report. These are:

  • Southdowns makes no reference to the possible added noise nuisance that fast onset rates may cause, which I mentioned in Another thing worth ignoring (posted 21 May).
  • The inappropriateness of using A-weighted noise measurements, which I raised in A weighty matter (posted 26 Jun), has not a matter that Southdowns has commented on.
  • The failure of HS2 Ltd to provide noise contour maps in the AoS, which I pointed out in Pass me the map (posted 30 Jun), is not mentioned by Southdowns.

In It’s on the level (posted 8 Jul) I discussed the three noise ranges that have been used in the AoS to classify nuisance levels into “red dot”, “yellow dot” and “grey dot” severity. Southdowns has provided much additional insight into the appropriateness of these classifications, and I will examine its criticisms of these in future blogs.

Southdowns has also raised a number of issues which I have not covered in my blogs, and I intend to look at these first, starting in my next blog.

So what conclusion does Southdowns come to about the way that noise nuisance has been assessed in the AoS? It says:

“The noise criteria and assumptions incorporated into the HS2 noise model represent a significant project risk in the event that significant noise effects have been underestimated and engineering alignment options are constrained to the published alignment. Options for additional mitigation will then be limited to the installation of higher noise barriers at 4- 5m height or more above ground and/or long term speed restrictions.”

Or as I put it in The end of the line:

“That HS2 Ltd has produced a technical assessment of noise for the Appraisal of Sustainability that has so many holes in it and questions against it is, to say the least, unfortunate.”

Southdowns has expressed its reservations in the more restrained, and frankly more obscure, language that is used for technical reports these days, but I think that we are both saying the same thing.


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