That’s much louder than the average

Environmental aspects of the 51m consultation response, part 18

In this blog I will continue my review of what Southdowns Environmental Consultants Ltd has said in Appendix 18 to the 51m alliance response to the public consultation (available here), which refers to criticisms that I have already made in earlier blogs.

In Taking a longer-term view (posted 22 Jun) I expressed the view that the sole use of the equivalent continuous noise level is not a satisfactory way of quantifying the noise nuisance caused by high speed trains. The Southdowns report does comment that the AoS relies on a single noise indicator only, this being the 18-hour LAeq noise level between 06:00 and 24:00 hrs, and identifies three “justifications” given in the AoS for using this parameter:

  • It “is used in the assessment of eligibility for sound insulation for new railways under the Noise Insulation Regulations” (available here).
  • It “is one of the noise indices that forms the basis for noise mapping under the Environmental Noise Regulations” (available here).
  • Its use is set out in DfT WebTAG guidance for the assessment of different transport proposals (available here).

The Southdowns report does point out that LAeq,18hr is only defined as a “supplementary noise indicator” in the Environmental Noise Regulations. However, since the two mandatory noise indicators in those regulations are also variants on the equivalent continuous noise level, this does not represent any case that the use of this equivalence methodology is inappropriate for high speed train noise.

The Southdowns report does however make the following, albeit fairly muted, criticism of the sole reliance by the AoS on the equivalent continuous noise level:

“However, the stated number of people that will experience a change in annoyance (long term) is based on steady state dose response curves derived from studies of community response to noise from established sources of transport noise. They do not address community response to changes in noise levels from new sources of noise in the environment and may not apply to community response to high speed railway noise, as acknowledged by DfT and Transport Analysis Guidance (TAG) which states that further research is needed to assess the annoyance response to different sources of transport noise such as high speed rail.”

This is fairly disappointing, but not entirely unexpected; after all the Southdowns report was written by engineers working in a discipline where the use of equivalent continuous noise level to assess annoyance levels is widespread. However the report does make one comment which illustrates just why the sole use of LAeq,18hr is not appropriate for HS2; this is that LAeq,18hr for the 432 train pass-bys estimated for the initial phase of the project will be 14 dB lower than the noise from a single train pass-by. The Southdowns report calls this “a significant margin” and concludes that “individual train pass bys will be noticeable in many tranquil environments where average train noise levels fall below 50 dB LAeq,18hr, particularly those which are not currently subject to noise from major infrastructure or other sources”.

In Taking a longer-term view I pointed out that the World Health Organisation had expressed reservations about the sole use of equivalent continuous noise level to assess noise nuisance “when there are distinct events to the noise”. Since I wrote this, my attention has been drawn to a document specifying noise limits for the “Bullet Train” (Shinkansen Superexpress Railway) issued by the Ministry of the Environment of the Government of Japan, which is available here.

I am pleased to report that the noise limits imposed by the Japanese Government are expressed in terms of the unit LpASmax, which is a measure based upon the maximum peak energy of a single train pass-by. At least one administration appears to realise that equivalent continuous noise level is not the best way of assessing the noise nuisance caused by high speed trains.

Acknowledgement: My thanks are due again to Terry Brennan, this time for finding the Shinkansen noise limits document.

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