Putting us on the map

If you are unfortunate enough to live within one kilometre of the proposed route of HS2 Phase 1, then you might find it interesting to consult the series of Environmental Statement (ES) reports Operational assessment sound, noise and vibration, identified as SV-004-0xy, where “xy” is the community forum area number in which you live; in my case the relevant report is SV-004-017. If you do download the report relevant to your location, you should search through the rows of table 1 to see if your street gets a mention.

When I did this, I found to my surprise that my house, and those of five of my neighbours, have been clustered together and identified as a “residential receptor” of noise from HS2 train operations. We have also been honoured by being granted an identity number (“ID”) for our cluster, which is 213490. Not only that, but we are marked on one of the maps in the ES; it’s SV-04-046 in Volume 5 Map Book Sound, noise and vibration – Country North.

The reason for my surprise at this discovery can be appreciated from the section below of map SV-05-046 in Volume 2 Map Book CFA17.

Noise prediction and measurement locations in east Cubbington (Source: HS2 Ltd)

Noise prediction and measurement locations in east Cubbington (Source: HS2 Ltd)

I have identified the location of cluster ID213490 on the above map by the blue letter “A”. You can see that it is well outside of the 40dB night (50dB day) noise footprint; in fact the cluster is very nearly twice as far from the proposed track centreline as the edge of the footprint. However, the “Day” column in the “Proposed Scheme only” section of table 1 in Report SV-004-017 indicates that LpAeq,07:00-23:00 is predicted to be 50dB at my receptor cluster. So it appears that the daytime noise that HS2 inflicts on me and my neighbours will be the same as if I was on the very edge of the noise footprint, rather than the impression given by the footprint that HS2 Ltd has published that we are well away from the high-noise area.

The situation is even worse when the figure in the adjacent column of table 1 is considered. This estimates that our night noise will be 43dB LpAeq,23:00-07:00, which is 3dB higher than the level at the edge of the footprint.

Report SV-004-017 does not even mention these apparent discrepancies, let alone explain them, so we are forced to speculate. There are two possible reasons that I can think of. The first relates to a statement in paragraph 4.3.4 of Report SV-004-017:

“Where the Proposed Scheme modifies an existing source, i.e. road or railway realignments, the Proposed Scheme only level in the table includes the sound from the modified source.”

So, in some cases, the predicted noise level has been upped to take account of noise from existing road traffic increasing due to the path of the road being shifted closer to the receptor location, or the road being elevated. As can be seen from the above map, there is a planned realignment of a road near to receptor ID213490, which includes increasing the height of the road by up to four metres. However, at its closest pass to the receptor the road alignment is unchanged, and I am not convinced that the proposed changes necessarily account for the unexpectedly higher level of operational airborne noise.

The second possible reason is that the impression given in the maps published by HS2 Ltd that the noise footprint is a continuous area and that all points outside of it will experience a lower noise level is misleading. A properly detailed computer-generated plot of noise levels will display “holes” with noise levels below the threshold chosen for the footprint limits and “islands” of higher level outside the footprint; this in my engineering experience is normal, and is mostly due to undulations in the terrain and local screening effects. So it could be that receptor ID213490 is in one of these “islands” of higher noise.

There is, of course, a third possible reason, which is that the given figures in table 1 for receptor ID213490 are in error. However, this is unlikely as there are similar examples in table 1 of receptors outside of the noise footprint with predicted levels in excess of the threshold.

I can’t help thinking that perhaps HS2 Ltd could have been a touch more helpful here. A column of notes in table 1, explaining any special circumstances involved in the calculation of the tabulated noise levels, would have avoided the need for speculation.

Something else that bears mention in passing is that the difference between the day and night operational noise levels predicted for my cluster is 7dB (50dB-43dB), not 10dB as claimed in footnote 151 on page 150 of ES Volume 1. It is not unusual to find discrepancies of this sort when using prediction tools (see footnote), and the numbers that the computer model spews out should only be considered estimates. However, an uncertainty of as much as 3dB is on the very edge of what might be considered a reasonable engineering tolerance, as a change of 3dB in level is generally acknowledged as perceptible.

Section 1.3 in Annex D2 to ES Volume 5 Appendix SV-001-000 claims that “the difference between predicted and measured sound levels is typically within ±3dB(A)”. However, the same section also illustrates that, in the real world, there can be wide variance between predicted and individual measurements, due to meteorological and other effects.

So the lesson to be drawn from all of this is not to place too much reliance on the footprint drawings that have been published by HS2 Ltd.

In the next posting I will examine the data in other columns of table 1 in Report SV-004-017.

Footnote: The difference between the day and night levels quoted for the 91 receptor locations for operational airborne noise identified in table 1 in Report SV-004-017 varies between 7dB and 12dB; the average difference is 8.6dB. HS2 Ltd has drawn the noise footprint on the basis of the calculated 40dB night noise contour, so the assumption that the same contour may be used for the 50dB day footprint is safe providing that the day/night difference is 10dB or less.

Acknowledgement: The Ordinance Survey mapping upon which the noise contours, route design and receptor locations are overlaid has been reproduced in accordance with the principles of fair dealing as set out in the Copyright, Designs and Patents Act 1988.  On this basis, this mapping is:

Reproduced by permission of Ordnance Survey on behalf of HMSO.

© Crown Copyright. All rights reserved.

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4 responses to this post.

  1. Posted by chriseaglen on February 28, 2014 at 8:20 am

    please raise this in a submission to the environmental audit committee in the next week. It may help many hundeds of people with double glazing and noise mitigations. Hs2 should have measured noise with the helicopter overflights but dont want the results confirming even higher levels due to different spectra.

    Reply

  2. Posted by Paul Thornton on February 28, 2014 at 10:02 am

    Peter,

    Very helpful article as ever. Could you spoon feed me further and clarify where one finds the number “xy” that they gave to each forum area? BW

    Paul

    On Fri, 28 Feb 2014 06:00:37 +0000

    Reply

    • Paul, if you click on the link “reports” in the first paragraph of “Puttin us on the map” and scroll down the page that opens up, you will see all of the CFAs, and the noise reports for each area, listed out from CFA01 Euston Station and approach to CFA26 Washwood Heath to Curzon Street.

      Reply

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