A delay in arrival

I am one of those unfortunate people who like to arrive in plenty of time. When it comes to catching trains this trait inevitably means that I have to wait long periods on station platforms, having arrived ridiculously early for the scheduled departure time. On such occasions I can find the station announcements a welcome distraction to while away the minutes; they always seem to be apologising for something, one of the most common being “a delay in the arrival” of a particular service.

HS2 Ltd appears to be starting as it means to go on – we have suffered a more than two year’s delay in the arrival of noise contour maps, and we didn’t even get an apology!

I complained about the absence of these maps long ago in my blog Pass me the map (posted 30 Jun 2011); since this remains the most viewed blog on this site, by far, it appears to be something that has concerned my readers also. Anyway, at last we have noise contour maps, although only for Phase 1 of course. They have turned up in the Draft Environmental Specification (DES) that was published on 16th May 2013. They may be found in the twenty-six “map books” that form part of the assemblage of documents that comprise Volume 2 of the ES. If you want to see the maps for your own area, select the map book for your community forum – my own, Offchurch and Cubbington, is Community Forum Area 17 for example – and turn to the section at the back “Map Series SV-01 – Operational Sound Contour Maps and Potential Significant Effects”.

You may have noticed that what I call “noise contour maps” are referred to by HS2 Ltd as “sound contour maps”. Now me, I call a spade a spade, but HS2 Ltd has always been a trifle touchy about the use of the words “sound” and “noise”. There is a long paragraph (14.1.2) in the document HS2 London to West Midlands EIA Scope and Methodology Report, which I won’t reproduce in full. This paragraph quotes from the Noise Policy Statement for England: “… sound only becomes noise … when it exists in the wrong place or at the wrong time such that it causes or contributes to some harmful or otherwise unwanted effect, like annoyance or sleep disturbance”. So it’s a bit like the way that wildflowers become weeds once they try to grow in your garden. According to HS2 Ltd the distinction used in its documentation is to employ the term sound, “until the assessment methodology evaluates that there is a potential adverse effect on a receptor, at which stage the term noise is used”.

Now that’s a bit pedantic, isn’t it? What’s more HS2 Ltd doesn’t appear to stick to its own rules in the case of the contour maps. After all, the contour maps are all about showing where there is “a potential adverse effect on a receptor”, so surely they are “noise contour maps”. The Civil Aviation Authority appears to be perfectly happy to talk about “noise contour maps”, so I don’t see why HS2 Ltd is being so precious.

Anyway, now I’m being pedantic; let’s move on.

Each of the maps has the same information panel, providing a key to the colour shading overlaid on the map, placed in the top right-hand corner of the sheet.

noise_contour_map_legendEach colour indicates that the daytime (16 hour) or night-time (8 hour) equivalent continuous sound level lies with a specified range of 5 dB. Exceptionally the loudest band of colour indicates >70 dB (day) or >60 dB (night) and no colour shading at all indicates <50 dB (day) or <40 dB (night).

The important thing to remember with these contour maps is that the noise doesn’t stop at the edge of the coloured areas, it just reduces to a level that HS2 Ltd considers acceptable and miraculously transforms itself from “noise” into “sound”; you may not share this view when you get to hear it.

Something that you should discern about the colour shading is that the same colour tone is used for daytime and night-time, but with a 10 dB offset. This reflects the 10 db difference between the threshold values chosen by HS2 Ltd for day and night – 50 dB and 40 dB, respectively. That it is possible to use the same contours for day and night is due to a convenient factoid claimed in the text of the community forum area reports in Volume 2 of the DES:

“With the train flows described in Volume 1, the night-time sound level (defined as the equivalent continuous sound level from 23:00 to 07:00 or LpAeq, night) from the Proposed Scheme would be approximately 10 dB lower than the daytime sound level.”

This statement is reproduced in paragraph 11.6.3 of virtually every one of the area reports, the exceptions being 3, 4, 5 and 8, which are exclusively tunnelled sections to which considerations of airborne sound don’t apply. Being me, I thought that I should check the calculation; it is a fairly simple piece of maths that I used in my blog Silent night? (posted 3 Dec 2011). When I did that calculation then, I made the day/night difference about 5 dB, but this was based upon the traffic patterns in the Appraisal of Sustainability and on an eighteen-hour day period rather than the sixteen hour period that HS2 Ltd employs now. So I was willing to accept that the figures may have changed, but was a little sceptical that the day/night difference might have changed quite so much.

So I delved into Volume 1 of the DES, seeking the information on the “train flows” that the statement in paragraph 11.6.3 promised would be there. I could find only two relevant statements in the whole volume. In paragraph 3.3.5 it says:

“The current assumed initial service pattern is for 11 trains per hour (tph) in each direction during peak hours. Based on the current version of the service specification, it is expected that later during Phase One the Proposed Scheme could operate up to 14tph in each direction during peak hours.”

Paragraph 5.12.18 tells us slightly more:

“It has been assumed that passenger services will start at 05:00 and that there will be a progressive increase in the number of services between 05:00 and 07:00. In general the peak level of service is assumed during the day to be between 07:00 and 21:00. There will then be a progressive decrease in the number of services after 21:00 until close of passenger services at 24:00.”

Unfortunately, this information is insufficient to enable the day/night noise difference calculation to be checked.

Now why does that not surprise me?

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4 responses to this post.

  1. Posted by Andrew Gibbs on June 13, 2013 at 2:10 pm

    Of course the night time section is where the average calculation really becomes bogus – it only takes one train at 5am to wake you up nice and early, and even a few tph in that period will make sure you don’t get back to sleep…

    Reply

  2. The real dishonesty in taking the noise from HS2 as a continuous equivalent sound is that this can only be properly applied to road traffic noise because it really is continuous. Railway noise is intermittent so the only honest way to assess it is to consider the PEAK sound level.
    Presumably HS2L have amended the average noise level they expect from the line to account for the fact that they proposed 14 trains per hour and now propose 18 tph.
    Incidentally, the definition of noise is “unwanted sound”. So all sound emanating from a railway you don’t want built can be defined as noise

    Reply

  3. Posted by chriseaglen on June 14, 2013 at 8:10 pm

    We cannot determine how these contours were produced with so few measurement locations. Also near the IMD Calvert there will be overnight movements and train maintenance and at depots movements. There is the need in some locations to allow for crossing noise additions also. There is also a significant amplitude modultation effect in some areas depending on power and if there is passing tree lines or buildings which also modulate the noise. There is likely to be some vortex effects also in some areas.

    Reply

    • Thanks Chris. Your comments have made me realise that there are two important points about the contour maps that I didn’t mention in the blog.
      Firstly as far as I can see, the maps take no account of the existing noise level measurements that HS2 Ltd has been taking over the last few months; they are purely computer predictions of what HS2 noise levels will be. We are promised that the consideration of the impact level, as determined by the existing noise, will be in the final ES.
      Secondly, the contours are for scheduled train movements only and take no account of any other sources of noise.

      Reply

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