Keeping things quiet

This was originally published on Peter’s blog HS2 and the Environment.

In my blog Have you heard? (posted 12 Jul 2011) I reflected upon the possible reasons for the general incredulity at what they had heard – or not heard – of people leaving the HS2 sound booth demonstrations given at the 2011 roadshows. Since the visit of the Transport Minister to Japan, which I mentioned in my blog Turning Japanese (posted 10 Apr 2013), has got me back on to the subject of noise, I thought that I would take the opportunity to provide some further clarification of the comments that I made in Have you heard?.

I reported in Have you heard? that:

“The man from Arup told me that it had been assumed that these [noise absorptive] panels will reduce the train noise by around 20 dB.”

I said 20 dB because that was what I was told. However I now know that, if I had taken the trouble to read the glossy display panels that were provided at the larger roadshows, I would have seen the following diagram.

from glossy display panels at HS2 consultation roadshow
This is part of a depiction of relative sound levels, measured at 25 metres distance unless indicated otherwise, in the form of a thermometer diagram. Amongst other points on the “temperature” scale it shows “HS2 Train (no barriers at 225mph)” and “HS2 Mitigated (high performance barriers at 225mph)” – the latter is in green. No sound level figures are provided for these two points, but I have scaled them off from the diagram and written them in (93 dB and 76 dB). So according to this diagram, the assumed effect of mitigation is to reduce the sound level by about 17 dB, not 20 dB. Now that’s not a whole deal of difference, but I am pleased to put the record straight.

Further confirmation that my rather rough and ready determination of the mitigation benefit yields about the right answer may be obtained from the response to a request for information under the provisions of the Environmental Information Regulations (EIR) 2004 (FOI11-240B) provided by HS2 Ltd on 27th July 2011. Section 2 of this response gives some noise level figures for the Wendover sound booth demonstration. We are told, in section 1.2, that the mitigation assumed is “3m effective absorptive noise barrier” and that the demonstration is at a point that is 150 metres distant from HS2. Section 2 tells us that the “unmitigated HS2 train” sound level at the observation point is 79 dB LpASmax and that the “mitigated HS2 train (3m effective height barrier)” sound level is 63 dB LpASmax, so the assumed mitigation is 16 dB.

What FOI11-240B does not explain is what assumptions have been made to arrive at the 16 dB of mitigation used for the Wendover sound booth demonstration, so I submitted a request under the EIR provisions myself to seek this further information (FOI13-580). The response that I have received is quite enlightening; it illustrates just how important the assumptions made about noise source heights are to the calculation of barrier efficiency.

HS2 Ltd appears to have gone for the best possible case that the train noise source is “at rail level”. This assumption appears to be at variance with the supposition made for the Appraisal of Sustainability (AoS) of an “effective source 2m above head of the rail” for train speeds in excess of 300kph, as explained in the document Noise Source Height of High Speed Trains for the Appraisal of Sustainability. This document shows that this higher noise source height gives a better fit with data measured by SNCF and results in a calculated noise barrier efficiency of 10 dB, a very significant 6 dB less than assumed for the sound booth model.

I am rather at a loss to understand why HS2 Ltd has made different assumptions about effective noise source height for the sound booth demonstration and the AoS, and rather concerned that the sound booth model may be underestimating the noise level as a result. However, I think that it is only fair to give HS2 Ltd the chance to explain and have submitted a further request under the EIR provisions (FOI13-603) seeking this explanation.

I will let you know what HS2 Ltd has to say.

7 comments to “Keeping things quiet”
  1. I just came across a rather interesting legal precedent, and decibels don’t even get a mention!

    My concern is the East Midlands M42 corridor. I have today walked over an open bridleway bridge over the motorway. The traffic noise was frightening. It is regularly used by riders from a nearby stables. The effect on the horses was clearly visibly left showing on the floor of the bridge, results not generally noticeable along the rest of the bridleway. Our government who seem to have decided by themselves to build this white elephant fail to even show public rights of way on the route proposal maps. I would estimate such bridges over the HS2 cutting would cost well in excess of a million each. I have counted 35 rights of way being effected in Leicestershire alone. No proposals or budgeting is included in the plans. How can a “democratic” government be so arrogant?

  2. Increase in cost for hs2 yet according to the court the compensation offer was very poor so this cost as yet to be added .how can the country afford this project that no one wants we need to show them at the council elections

  3. Peter, the logic I go by is based on numbers and not on “because I say it’s right, it must be right!”
    Take the Stafford Area Improvements Programme (includes Norton Bridge) which, after many years of discussion, is now entering its final consultation phase. The initial consultation threw up several important issues of which Network Rail had not been aware – but did at least acknowledge.
    SAIP will enable two extra trains to run between London and the north-west every hour. There will also be an additional fast train between Manchester and Birmingham every hour, and one extra freight train passing through Stafford each hour – all by 2017. Now, there’s a number we’ve seen before – though the other numbers involved are not widely publicised.
    The full development will see significantly improved travelling times also because the lines will no longer be crossed. With HS2, they have not yet worked out how the Y intersection will be joined.
    Because SAIP was only a pipedream when HS2 started its own, the SAIP “numbers” could not be used in demonstrating the improvement HS2 will make, presumably because only “factual” facts and not potential ones could be used in the calculations – how frustrating this must have been! (a joke, of sorts, Peter).
    SAIP is a massive project not to be undertaken lightly and it hasn’t been. Retrofitting is of course more difficult than simply cuttings and pastings on greenbelt. Consultation has been thorough and the work appears not to require a significant amount of new land or disturbance so that compensation might be fair, or even generous, without breaking the bank. But all this time and effort over one little project? – HS2 will be a walk in the park.
    And the cost? Well, it’s reported as being £250m. Now there’s a number to conjure with. The money could have been in the bank had it not already been spent on another project.
    And where’s the logic? – in leaving this section of WCML as it is for so long? There is none.
    Best Wishes to the engineers involved – a project with logic!

    • Thanks for your in-depth response, which wasn’t necessary

      Needless to say the railway engineer profession is already well aware of projects such as the Stafford Flyover at Norton Bridge and, believe it or not, it has been factored into future rail capacity planning but we still need HS2 in the longer term – that’s what HS2 is all about remember – the longer term, not the next five or ten years.

      I realise that HS2 opponents struggle with the concept of planning for ten to twenty years out but that’s not my problem?

  4. How cynical is the system we now call democracy. A so-called mitigated HS2 is shown as having a lower noise pollution than a hair dryer. OCD is more prevalent these days but there cannot be many who would wish to dry their hair every 1-2 minutes throughout the day.
    At the same time Stop- it-HS2 reports ’51M’ councils spend over £1m opposing HS2 – Railnews’
    Railnews tries to imply that councils are wasting taxpayers’ money in trying to protect thousands of their constituents whose lives have been ruined by the mere proposal for HS2, while totally ignoring the £250m of taxpayers’ money (rising rapidly) already wasted on just promoting this madcap scheme.
    One imagines that Railnews aims to inform highly professional engineers in the industry. I can only hope that common sense and logic will prevail among this profession.

    • @mike: “I can only hope that common sense and logic will prevail among this profession”

      Don’t worry @mike – it has

      • Yeah right Padav. The logic that applauds as much government spending as possible in “their” particular industry regardless of the return and regardless of the environmental impact. Also regardless of the nation’s financial state.

        Better infrastructure propostitions would in fact be a serious effort to build some social housing to deal with the 2.2 million homes deficit or to build some power generating capacity so that we don’t get power cuts within the next few years ( the Severn Barrage would cost less than HS2 and generate 8 % of the nation’s electricity requirements ).

        Or , and I know this is unfashionable , you could actually invest in public services. There was a report today saying that NHS wards regularly operate at unsafe staffing levels.

        All depends on your priorities. We know what the priorities for Rail News are. I should think Sim and Alan are getting quite excited at the prospect of those sleek train curves and ramrod straight tracks.

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