“We don’t believe you”

The effects of speed, part 5

The title of this blog is not my own personal condemnation; it is attributed to the Transport Secretary in an article in the Sunday Times of 27th February 2011. He was talking about a plan to play simulations of train noise to visitors to the HS2 Ltd roadshow that is touring now. The full quote is:

I’m expecting that the predominant reaction when people hear the sound simulations will be “we don’t believe you”, because they’ve been led to believe that it’s going to be like an aeroplane landing on a runway or like living near Heathrow airport.

The problem is of course that we will not know what the train actually sounds like until test services start running, which is not likely to be until towards the middle of the 2020s. By then the noise mitigation will have all been decided and it will probably be too late to change things. The only likely recourse if the noise turns out to be worse than we have been told will be to apply for grants to pay for noise insulation to be applied to properties or to seek compensation for putting up with it.

So it is important to know that what HS2 Ltd tells us about noise levels can be trusted. I’m afraid to say that I am beginning to doubt that this is the case, since it appears to me that HS2 Ltd is seeking ways to understate the noise pollution levels. So far my investigations have uncovered two specific ways in which HS2 Ltd is doing this.

Firstly there is the question of the maximum running speed specification, which has been set at 400 kph (250 mph). Since HS2 is being designed to support this speed, you would expect that noise pollution levels would be calculated at, and noise mitigation would be designed for, this speed. Well no, actually. The noise is being worked at 360 kph (225 mph).

This is confirmed, somewhat obliquely, in paragraph 5.6.4 on page 45 of Appendix 5.4 to the Appraisal of Sustainability Main Report (which can be found here). The reason given there for restricting noise estimations to a maximum speed of 360 kph is that this requirement is “listed in the HS2 Project Specification”.

A more helpful explanation was given to attendees at the Technical Seminars hosted by HS2 Ltd in November last year. In response to a question about why they were not looking at noise at 400 kph, the HS2 Ltd noise engineers said that the hope was that when 400 kph trains are introduced design advancements would mean that they would be no noisier than the first-generation trains on HS2 that would be limited to 360 kph. This is a similar argument to the one that I revealed in my blog of 17 May, which is already being used by HS2 Ltd to downplay the loudness of the aerodynamic noise and the height of noise barriers required to counter it.

So in its calculations HS2 Ltd is not only relying on noise reductions in the first generation of HS2 rolling stock compared with current high speed trains, it is also depending on the second generation of HS2 trains improving further on the first.

Fortunately the Ladbroke action group has looked at noise nuisance caused by high speed trains at both 360 kph and 400 kph and so we are able to quantify how much HS2 Ltd has shaved off by ignoring the impact of 400 kph trains. The report produced by Ladbroke can be found here. The Ladbroke group has employed the methodology prescribed by the US Department of Transport Federal Railroad Administration to predict noise levels; you will remember that I first introduced the US FRA manual in my blog of 17 May.

The Ladbroke report contains two tables, 4 and 5, which are presented on pages 8 and 9. Table 4 predicts noise levels at increasing distances from the track at 360 kph and Table 5 does the same at 400 kph. I wish to concentrate on the column “single train pass SEL dBA” as this looks at the effect of a single train pass and thus ignores the impact of any assumed operational service patterns. This is important as different train pass frequencies have been assumed in constructing the two tables.

Comparing the SEL dBA values for the same distance from the track across the two tables shows that the noise for 400 kph is in excess of 2 dB higher at all distances.

To those of you not familiar with the dB (decibel) I apologise. I intend to devote a series of blogs to explaining this concept in the very near future. Meanwhile, if you have a burning need to sort this out for yourself the Wikipedia article is here. However, for the purposes of this blog please just take it on trust and treat it like any other unit.

You may remember that in my blog that was posted on 17 May, I mentioned the slight of hand tucked away in paragraph 6.3.5 on page 50 of Appendix 5.4 to the Appraisal of Sustainability Main Report. This paragraph reveals that HS2 Ltd is assuming that “advanced rolling stock” which will be used for the first-generation trains on HS2 will reduce the noise power emanating from the train. The assumption made is that a 3 dB reduction can be assumed, compared with current rolling stock (e.g. TGV).

So the two assumptions together have allowed HS2 Ltd to reduce the noise nuisance prediction by a shade over 5 dB, compared to what might be regarded as prudent (i.e. assuming that future trains will be no better than what is achievable now).

If we look again at the “single train pass SEL dBA” column of Ladbroke’s Table 4, we can see what a 5 dB increase in noise means in terms of distance from the track. So if, for example, we look at the level at 150 metres from the track, the figure in the column is 93.0 dB. If we increase the source by 5 dB, all of the levels will increase by the same amount and the level at 300 metres will become 93.2 dB, so the 93 dB level has moved out to nearly 300 metres. Similarly the level at 250 metres moves out to between 400 and 500 metres. So the distance nearly doubles in each case.

So by using these two devices HS2 Ltd has virtually halved the predicted distance from the track where unacceptably high noise levels will occur. So if you were surprised by claims by HS2 Ltd that only ten dwellings on the London-Birmingham route will experience “high noise” you will now understand one reason for this optimism.

Can we really trust what HS2 Ltd says about noise?


5 responses to this post.

  1. What I find most extraordinary is the concept of average noise used by HS2 – it is like calculating the average pain inflicted in a boxing ring over 2.5minutes minutes when Mike Tyson is hitting you every 7 seconds between intervals of working out where to hurt you next. I say 2.5 minutes because they adopt the average over 18hours per day – what is going on in the other 6 hours?: ah, that must be when we drug ourselves to sleep…


    • Hi Michael
      Yes this concept only really works with noise that is reasonably continuous, not in bursts like high speed trains or aircraft. We are not alone in thinking that it is the wrong way to do it, the World Health Organisation is not happy that this is a true indicator of the annoyance level either.
      There will be a future blog about this.


      • Yes, indeed, it is a non-sensical approach dreamed up by a committee to ameliorate the problem – and it avoids the clear conclusion, in my analogy, that Mr Tyson hitting you every 7 seconds fro 2.5minutes will almost certainly render you brain-dead for ever after…everybody knows that repeated audio blows to the eardrums are an effective form of torture.

      • Hi again Michael
        The strange thing is that it can also work the other way. The pressure group Airport Watch has issued a briefing sheet “How Aircraft Noise is Measured … and how it is flawed”. In this document it cites an interesting result thrown up by averaging measurements at Heathrow. It says that four hours of Boeing 757 flights, one every two minutes, caused the same noise nuisance according to official measurements as one Concorde flight followed by 3 hours and fifty-eight minutes of quiet..
        All you can say is that the “equivalent continuous noise level” is a totally flawed method.

  2. Excellent piece, thanks. Not the only sleight of hand by HS2 (eg. cost of removing spoil from tunnels and large cuttings is not costed at all. Of course they can’t be trusted. The default position for any such project is ‘how do we spin this’ . For the same reasons the costs cannot possibly be correct. If the Olympic project is costing £9B how can this cost just £17B when a large part of north and west london has to be rebuilt? Just getting to Harefield will cost £15B


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