I think that you may still be missing something

In So that’s why you ignored it (posted 11 May 2012) I observed that, whilst the noise generated by a train pass-by would be exactly the same by day and by night, it was a peculiarity of the equivalent continuous sound level calculation that, at any given location, LAeq, day will exceed LAeq,night by about 5 dB(A). To put this another way, by day the peak level of a train pass-by will be around 14 dB(A) higher than the equivalent continuous sound level (see note below), but at night this difference will be (14+5), or 19 dB(A), higher.

This is another good illustration of why the equivalent continuous sound level does not give a complete picture of the noise nuisance level, but it also reinforces the argument that I made in my blog A rude awakening (posted 11 Dec 2011) that further consideration needs to be given to the possible sleep disturbance effects of peak noise levels at night.

As an illustration of this point, consider a bedroom where the façade of the building where the bedroom is located is experiencing an incident noise level from HS2 of 40 dB(A) LAeq,night, which is, of course, the NNG. The peak noise level incident on that façade will be (40+19), or 59 dB(A). The Night Noise Guidelines for Europe (here) discusses, in paragraph 1.3.4.4 on pages 9 and 10, how much the fabric of the building will reduce the noise level outside to arrive at a noise level actually inside the bedroom; it calls this noise reduction the “insulation value”.

The same paragraph in the Night Noise Guidelines for Europe gives typical values for the insulation value of 15 dB with windows open and 30 dB with windows closed, and opts for a year-round average figure of 21 dB. So a noise level just on the NNG outside will give a peak level in the bedroom of 44 dB(A) (59 dB(A) -15 dB(A)) with windows open and 38 dB(A) (59 dB(A) – 21 dB(A)) as a year-round average.

In A rude awakening I explained that WHO night time noise guidance prior to the publication of the Night Noise Guidelines for Europe recommended both equivalent continuous and peak noise level limits. The recommended maximum peak noise level within the bedroom then was 45 dB(A); even with windows open the NNG equivalent continuous threshold will trigger before this peak is exceeded.

As I also explained in A rude awakening, the Night Noise Guidelines for Europe adopts the equivalent continuous sound level as the sole metric for its night noise recommendations; it does this to “be consistent with existing practices in the legislation”. However, this same document also acknowledges the position taken by the WHO previously that the maximum sound level per noise event is also relevant to considerations of sleep disturbance. It also concludes that the earlier recommended maximum peak level may have been set too low, as “thresholds are now known to be lower than LAmax of 45 dB for a number of effects” (page xviii of Night Noise Guidelines for Europe). Data presented in Table 1 on page xiii indicates that physiological effects may be observed at peak noise levels as low as 32 dB LAmax,inside.

So even with all windows closed the peak level in the bedroom caused by a sound level just at NNG level outside will exceed, by an appreciable margin, levels which the WHO has acknowledged may cause physiological effects.

So even though the adoption by HS2 Ltd of the WHO NNG is very welcome, there is still cause for concern that the high peak to equivalent continuous ratio exhibited by HS2 noise, particularly at night, may mean that health risks caused by peak noise in the bedroom at lower levels will still be overlooked. My suggestion is that HS2 Ltd should commission a thorough review of this matter.

Note: The origin of this 14 dB(A) may be found in my blog I only just noticed that (posted 25 Apr 2012).

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2 responses to this post.

  1. Posted by Dr Chris Eaglen on May 15, 2012 at 6:22 pm

    Observations with the Javelin trains near Rainham at 40m from the line and at a height of the pantograph determines the passing train noise levels are more noticeable/disturbable than the dB level combination suggests. The HS2 more frequent passing occasions due to the high frequency than the Javelins suggests HS2 impacts will be more disturbing than the Eurostar lower frequency power car outputs. There is proximity distances of 350m to 400m alongside Aylesbury with some surface level and viaduct elevated sections where there is likely to be significant impacts on some of the vulnerable people in Walton Court. With the failure of HS2 to agree to move the route 3 further away from Aylesbury and the failure to fully assess Route 4 it is realised the AOS failed and the EIA draft is also failing to fully characterise specific sections and combinations of noise generation from two passing rakes. It is agreed that thorough reviews would be helpful but the proposed scheme is now in the aborted cost phase if Route 3 is changed or Route 4 is re-examined.

    Reply

    • Hi Chris. I agree that HS2 noise is likely to be much more problematic than HS1.

      On the specific issue of the higher contribution of the pantograph at very high speeds, I was shocked to read in paragraph 7.2.5 on p. 27 of “Review of HS2 London to West Midlands Appraisal of Sustainability” that HS2 consider that “its significance is often overstated”. According to that same paragraph “The wheel-rail interface will remain the most significant part of the noise from the train, even at high speed”.

      HS2 Ltd appears to base its view on research undertaken by SNCF and I have been delving into papers published out of this research to try and understand where the optimism is coming from. I am planning to report of this in blogs this summer, but I have to say in advance of this that I can’t agree with the HS2 Ltd standpoint (there’s a surprise).

      I will continue to seek to raise this topic, and all the other issues with HS2 noise, with HS2 Ltd using all of the avenues that may become available. I don’t intend to give up on this as I consider that noise is an important, and potentially very disruptive, element of HS2 environmental impact. However, I recognise that the only official communication link that I have at present with HS2 Ltd is my local community forum, and that it may not be the most appropriate place for detailed discussions on noise impacts.

      Reply

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