Not quite measuring up

Assessing the annoyance caused by HS2 noise, part 1

As was the case with Further down the line (posted 10 Oct 2012), I feel compelled to write this current short series of blogs by comments that have been made on this site.

I will start from a basic tenet of the HS2 Ltd creed that appears in paragraph 7.2.7 on page 27 of the document Review of HS2 London to West Midlands Appraisal of Sustainability:

“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.”

The use of the equivalent continuous sound level (LAeq) to assess the nuisance caused by noise is a subject that I have discussed in a number of  blogs:

  • In Taking a longer-term view (posted 22 Jun 2011) I provided a short tutorial on the meaning of the equivalent continuous sound level parameter and its limitations.
  • In That’s much louder than average (posted 29 Nov 2011) I reported on what Southdowns Environmental Consultants Ltd had said about using the equivalent continuous sound level parameter in the 51m response to the public consultation.
  • In Going over some old ground (posted 17 Apr 2012), amongst other things, I reviewed what respondents to the public consultation had said about the use of the equivalent continuous sound level parameter.
  • In May I suggest a better option? (posted 21 Apr 2012) I proposed that Lden should be used as the equivalent continuous sound level parameter.
  • In I only just noticed that (posted 25 Apr 2012) I propose that peak noise also needs to be considered.

Now I may be about to surprise you, but the result of all of my deliberations on this subject is that I do not disagree with the HS2 Ltd statement that I have reproduced above. However, and perhaps this won’t surprise you, I do disagree with the way that HS2 Ltd has translated this statement into the parameters that have been employed for the HS2 London to West Midlands EIA Scope and Methodology Report (here). In other words, the Devil is in the detail and I will try and explain, in as succinctly and jargon-free a way as I can, why I consider this to be the case.

In order to kick off this explanation I shall return to the diagram that I borrowed from a Civil Aviation Authority website and used in my blog Taking a longer-term view. Whilst I am at it, might I suggest a revisit to this blog if you want to brush up on the equivalent continuous sound level parameter?

Equivalent continuous sound level (source: CAA)

The equivalent continuous sound level method characterises a sound waveform that varies with time, such as HS2 noise, by summing the energy of that sound waveform, instant by instant, over a set period of time. An equivalent continuous sound level (i.e. one that doesn’t vary with time) is then calculated to characterise the varying waveform; this is illustrated on the diagram by the horizontal line, labelled “average sound energy”.

Now the sceptics amongst you may observe that the two waveforms, wiggly and straight, are very different animals and you may wonder just how good a characterisation the equivalent continuous sound level is. If you think this, then go to the top of the class; I will come back to this in the blogs that follow in this series. However, this method is, as HS2 Ltd points out in the quote at the top of this blog, ubiquitous within the acousticians world and I’m not about to try and demolish this venerated foundation stone.

And, to be fair, the method has one big plus when it comes to using it for railways; each train pass-by will contribute a packet of energy to the summation. So for example, this packet of energy will, like for like, be bigger for HS2 than HS1, because HS2 will normally be much faster. Also, the frequency of HS2 services will be much higher than HS1, and so more packets of energy will be contributed by HS2 every hour. So, like for like, the equivalent continuous sound level calculated for HS2 will be higher than for HS1; so at least the method is capable of distinguishing that HS2 will be worse than HS1.

The time period over which the summation is to be carried out is proposed in the HS2 London to West Midlands EIA Scope and Methodology Report as 16 hours; this has been reduced from 18 hours used in the Appraisal of Sustainability, for a valid reason that I will not go into now.

The equivalent continuous sound level is presented as a decibel value and will be calculated for “receptors” along the route; such a “receptor” might be your house or the village school, perhaps. The problem is that you really don’t care how many decibels will be hitting your house, do you; what you really need to know is what it is going to mean to your health, temper and lifestyle. This nitty-gritty of what the noise will mean to you is summed up in the concept of “annoyance”, and relating decibels to annoyance is by no means a simple task.

This is something that I mean to look at in my next couple of blogs, where I will demonstrate that HS2 Ltd is “not quite measuring up” to the task of making the best possible shot of estimating the annoyance that HS2 noise will cause.


2 responses to this post.

  1. Posted by chriseaglen on October 14, 2012 at 9:23 am

    There is work underway at NPL on the impacts on the person and the responses. You cannot measure these repeated noises by dB values. It gives a sense of loudness but the person responds naturally in fright or flight terms. Try living under a flight path over 30 years and you will realise that no one ignores all noise even after such exposures. Lets the objective scientists at NPL help you rather than making desktop propositions please. Many people along the route will have a change of the lives from this and partial advice is not the way to treat this new context.

    Al people dealing with airport noise and the viewers of F1 know the passing cars wake them from slumber as will do HS2 very different the infrequent Eurostar but the Javliins passing by Rainham in Essex fo disturb on crossing each way. Which the future mid-distant Javelin services will do.


    • I have not come across the NPL work Chris and would appreciate receiving any links that you may have to websites where I can learn more.
      My intention in writing this short series of blogs is to aim at making the case for a change by HS2 Ltd that I can reasonably expect to have some chance of success, bearing in mind the reluctance that HS2 Ltd has exhibited to question established UK methodologies. Since HS2 Ltd has referenced the World Health Organisation “Guidelines for Community Noise” in its own documentation, I will be basing my arguments largely on that document and will introduce it in the second blog in the series (“How annoying is that?, which is scheduled to be posted on 18 Oct 2012). Whilst the WHO document dates from 1999 and may not therefore represent the latest thinking, adopting its suggestions would represent a considerable advance on what HS2 Ltd is offering at present.


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