A very noisy bird

First publish on Peter’s blog HS2 and the Environment.

Part One

If my memory serves me correctly – and after around one hundred days of petition hearings my powers of recollection are not at their best – the expert testimony presented to the HS2 Select Committee on noise has, with one recent exception, been entirely from the Promoter’s side. That exception came in July this year when Halton Parish Council, Wendover Parish Council, The Wendover Society and Wendover HS2 jointly put up Steve Summers, a Member of the Institute of Acoustics and Associate Director of ACCON UK Environmental Consultants, as one of their witnesses (see footnote 1).

On the rare occasions when Rupert Thornely-Taylor has given evidence on behalf of the Promoter, he has, when faced only with non-expert petitioners, been able to assume the role of fount of all knowledge and play the friendly uncle to us poor schmucks who have dared to challenge the line we are being fed on noise, whilst failing to disguise his utter contempt for our obvious ignorance. As can be seen from his biography, Mr Summers is well able to trade CVs with Mr Thornely-Taylor, and the sight of the latter taking on someone his own size, so to speak, would have been an event to relish. Unfortunately, we were denied that pleasure. Tim Mould QC, Lead Counsel for the Promoter, appears to fancy himself as competent on matters acoustic and rebuffed the petitioners’ case himself, not calling Mr Thornely-Taylor to give evidence. In the process, I feel that he was guilty of a discourtesy to Mr Summers, an unfortunate impoliteness that was further exacerbated by insufficient time being allocated for his testimony due to “mixed messages” regarding timetabling (see footnote 2).

What we were able to hear from Mr Summers served to vindicate the complaints that have been made by a number of petitioners that HS2 Ltd’s preference for quoting noise as equivalent continuous sound levels tends to understate the impacts. His evidence was routed firmly in noise expressed as the maximum levels from train pass-bys (LpAFmax), and two exhibits that he employed clearly illustrated why this was his preference.

The first of these exhibits, A1212(11), reproduces one of the noise maps prepared by HS2 Ltd for Volume 5 of the Environmental Statement (ES). The exhibit shows the section of the proposed route of HS2 passing Wendover and the extent of the penetration of predicted HS2 operational noise that is above the lowest observed adverse effect level (LOAEL) into the town; locations predicted to experience levels above LOAEL are indicated by the shaded areas. In common with all such noise maps in the ES, the map employs the equivalent continuous sound level, LpAeq,T. LOAEL is taken to be 50 dB LpAeq,07:00-23:00 during the day and 40 dB LpAeq,23:00-07:00 at night; locations at LOAEL by day and night are assumed to be coincident. Mr Summers pointed out to the Committee that “the majority of Wendover town is outside of [the area where LOAEL is exceeded]” (see footnote 3).

However, subsequent to the ES being published HS2 Ltd issued Information Paper E20, which sets an alternative value for LOAEL at night of 60 dB LpAFmax (see footnote 4). Despite introducing this additional way of expressing LOAEL that employs the maximum train pass-by noise level, HS2 Ltd has made it clear that it does not plan to issue maps showing the maximum level, despite the opportunity that was afforded by the need for the Supplementary ES.

A glance at Mr Summers’ second exhibit, A1212(12), should explain this reluctance. On this exhibit Mr Summers has plotted the 60 dB LpAFmax contour in green, indicating the penetration of LOAEL night into Wendover using this alternative peak measure. This new map shows, in Mr Summers’ words, that “a large part of the town is above the lowest adverse effect level” – certainly much more of the town than if the equivalent continuous sound level is used to determine LOAEL and, as Mr Summers pointed out, up to 36 train movements an hour were possible on the line. From this part of his evidence it does look as though many Wendover residents can expect significant sleep disturbance due to HS2.

This apparent disparity between the maps for LOAEL drawn using LpAeq,T and LpAFmax has been brought to the attention of the Select Committee before; in December last year Cllr Andrew Burrow, a witness for the Berkswell Society, presented his exhibit A556(47) to the Committee. The exhibit is a map showing the areas of Berkswell that HS2 Ltd has predicted will experience peak noise in excess of 60 dB LpAFmax compared with the LOAEL night contour of 40 dB LpAeq,23:00-07:00. Cllr Burrow told the Committee how he had constructed this map (see footnote 5):

“… I took an HS2 map, which is this one, and I circled every noise-monitoring point – sorry, prediction point where the predicted noise was above the 60dB, but I ignored the TS1-compliant trains – i.e. the noisier trains – because I assume, with the abolition of the Channel Tunnel link, these will not occur, so I’ve just taken the noise-efficient new trains that HS2 are projecting”.

The conclusion resulting from this exercise that he presented to the Committee was:

“… you get quite a lot of red spots all over the place, and they’re outside, you will notice, the 40dB night limit, which is the grey shaded area, and a lot of them go deep into the Riddings Hill Estate.”


Part Two

In his evidence to the HS2 Select Committee, acoustics expert Steve Summers identified two particular “non-residential receptors”, to use the somewhat sanitised language of the HS2 Phase 1 Environmental Statement (ES), where he regards the operational noise levels predicted for HS2 as a cause for concern (see footnote 1).

The first of these is St Mary’s Church Wendover, a Grade II*-listed building, where Mr Summers revealed the predicted noise level from train pass-bys to be 70 dB LpAF,max outside the church, which he described as “high”. He said that he estimated that this would mean that the resulting level inside the church would be “in excess of 40 dB, probably up to 46 dB LAmax, and would be “likely to cause disturbance to concerts as well as other services or activities” (see footnote 2).

The second sensitive site singled out by Mr Summers was Wendover Campus School (aka Wendover House), a mixed special school. He told the Committee that the predicted noise level of train pass-bys outside the school is 71 dB and that this was “likely to equate to internal levels, allowing [for] windows and open ventilation, of between 56 and 61 dB, which is likely to cause disturbance to teaching and learning when windows are open” (see footnote 3).

In his cross-examination of Mr Summers, Tim Mould QC, Lead Counsel for the Promoter, asked him to consider three exhibits that had been prepared by HS2 Ltd.

The first of these P7494(2) displays the results of noise measurements taken inside St Mary’s during evenings when no events were taking place in the church (see footnote 4). Mr Summers observed that there was an error in that exhibit (see footnote 5); he indicated that the green bar at 40 dB should show 36 events, not 18, as this was the maximum number of train pass-bys. He was actually wrong about this; as I will explain in part 3, the bar chart is correct, as far as it goes.

The point of Mr Mould showing this exhibit to Mr Summers was to enable the QC to claim that “the [pass-by noise from] railway trains will be well within [the] existing range of noise levels [inside the church]” (see footnote 6).

Mr Mould made a similar claim for the pass-by noise predicted for some outside assessment locations “within and on the edges of the settlement of Wendover”, illustrated by exhibits P7499(1), showing the existing baseline noise level at these locations, and P7499(3), showing the predictions of impacts and effects due to operational noise (see footnote 7). Based upon these exhibits he put it to Mr Summers that a pass-by of a HS2 train will be “a new noise event, but it will not increase the peak noise experienced (sic) that people have within the settlement of Wendover” (see footnote 8).

There was some discussion that can cast some light on these claims by Mr Mould during Mr Summers’ cross-examination and subsequent re-examination by Nathalie Lieven QC. This discussion was initiated by a question posed by Mark Hendrick MP. He asked (see footnote 9):

“Where is the current noise coming from?”

Mr Mould suggested that the existing peak noise events that HS2 Ltd’s sound level meters had picked up were the result of (see footnote 10):

“Traffic, existing railway trains, people shouting in the street, all the things that make up the noise of existing life in a successful market town.”

But it was the suggestion from Mr Summers of another possible noise source that serves as a warning to treat measurements made with a sound level meter with caution; he suggested “a bird”, to which Ms Lieven added “a very, very noisy bird” (see footnote 11) – I told you in part 1 that ornithology would come into this tale!

The whole point is that it needn’t have been a noisy bird at all, it could just have been a fairly quiet bird perched on top of the sound level meter! You see, sound level meters can’t distinguish loud sounds a distance away from softer sounds close to; they can both register the same sound pressure level at the meter, which is all that gets logged.

The other thing that sound level meters are hopeless at doing is distinguishing an awful din, like a high-speed train passing, from a pleasant sound like, err, birdsong.

Mr Summers also provided a practical example of why the type of data that Mr Mould was basing his case on needed to be treated with caution (see footnote 12):

“I think [Mr Mould’s proposition that noise from the railway is broadly speaking within the range of the existing noise environment is] a very simplified view because obviously properties that are next to an existing road which has got a fair amount of traffic will have a high LA max, whereas other properties which are distant from the major roads will have a very low existing LA max.”

So I think that Mr Mould was probably on a bit of a sticky wicket with his claim of “much the same, only more of it”. He looked even more out on a limb when Mr Summers pointed out to him that for some of the locations shown on P7499(3) “the predicted maximum noise levels for HS2 are above the baseline LA maxes” (see footnote 13).

I think that his entry on the scorecard for this particular innings should be “T Mould – retired hurt” as he limped off covering his exit with (see footnote 14):

“All right. I’m happy with that. That’s the point I want to make. Thank you.”


Part Three

In part 2 I promised to explain why acoustics expert Steve Summers had been wrong to claim that there was an error in exhibit P7494(2) during his cross-examination by Tim Mould QC, Lead Counsel for the Promoter (see footnote 1). This exhibit includes a bar chart which displays two sets of data: the results of some peak noise measurements taken in the interior of St Mary’s Church Wendover, indicated by red-coloured bars; and, the results to be expected if a similar exercise is carried out once HS2 is running, shown by green bars. So it is essentially two bar charts in one, and it will be easier to consider the red bars alone initially.

Tim Mould told the HS2 Select Committee that measurements had been taken inside the church “over a series of five-minute intervals during an evening” (see footnote 2). That it is standard practice for HS2 Ltd to set the sound level meter to record in five-minute intervals is confirmed by paragraph 1.3.14 of Annex B to Appendix SV-001-000 to Volume 5 of the HS2 Phase 1 Environmental Statement. This paragraph also confirms that the sound level meter logs the highest value of LpAF,max detected during each five-minute interval.

The exhibit provides additional explanation of how the data has been captured by labelling the y-axis of the bar chart “Number of events during 7 day survey in evening period (19:00-23:00)”. So we know that on each of these evenings the sound meter was running for four hours and so would have logged 48 five-minute measurement intervals. Useful confirmation that this is along the right lines may be gained from totalling the individual lengths of the red bars displayed on the chart, which comes to 48 events.

Of course, the measurements were taken over seven evenings, not just one. What I assume HS2 Ltd has done is to take the average of the number of events falling in each bin of the bar chart over the seven nights, which appears to be a sensible approach. So what is displayed by the red bars is a typical evening, based upon seven evenings’ measurements.

The bins are labelled with integer numbers representing the highest value of LpAF,max logged during each measurement interval. No information has been provided on the range of values set for each bin, e.g. 45 dB might mean within the range 44.5 to 45.5 dB, but this is not really essential information for current purposes.

So far so good, but now we have to consider the green bars that show the effect of adding noise that is predicted to result from HS2 train pass-bys to the sound environment inside the church.

If we take worst case, then HS2 trains will cause 36 short bursts of noise to be heard inside the church every hour (18 on the up line and 18 on the down line). There will be fewer bursts, perhaps a little over 20, when only Phase 1 is operational, and the number of pass-bys will tail off leading up to midnight. However, I think that it is a fair assumption that at least one HS2 noise burst will occur within each five-minute measurement interval over the four-hour evening period used for the chart.

Something that I should point out here is that only one such burst is required to be logged in each measurement interval for maximum effect; a second, or further subsequent, burst will not change the data logged by the sound level meter, as it is merely duplication. So all you actually need to see the maximum change to the bar chart is 12 equally-spaced pass-bys per hour (6 each way), or one per interval; any increase in traffic above this level will have no impact on the bar chart. This is surely a shortcoming of this measurement method.

Mr Summers estimated that the HS2 noise bursts would give rise to levels inside the church “to be in excess of 40 dB, probably up to 46 dB LA max” (see footnote 3). True to form HS2 Ltd has taken the level to be 40 dB, no more; well, they would say that, wouldn’t they.

So what is the effect of adding at least one noise burst of 40 dB LpAF,max to each of the red bars? Let’s construct the green bar chart.

If the red bar refers to a level of 41 dB or more, then the LpAF,max of the ambient sound event is greater than the HS2 sound event, and so it is the ambient sound event level that will be logged for the time interval. This means that all red bars to the right of the 40 dB bar will be unchanged by the introduction of the HS2 noise, and so the green bars will each be the same height as the red bars.

If the red bar refers to a level of less than 40 dB, then the LpAF,max of the HS2 sound event is greater than the ambient sound event, and so it is the HS2 sound event level that will be logged for the time interval. This means that all of the red bars to the left of the 40 dB bar will have no green bar counterparts, and the green bar for 40 dB will be equal in height to the sum of all of the red bars to the left of the 40 dB bar plus the height of the 40 dB bar. This total is 18, which purely by coincidence is the same number as the maximum one-way trains per hour on this section of the HS2 route; this accounts for Mr Summers’ confusion.

Having confirmed that the green bar chart has been drawn correctly, we are left with the question of whether it tells us very much about the impact that HS2 trains will have upon those taking part in events inside St Mary’s Church. Clearly, the sections of the two bar charts to the left of the 41 dB bar are very different; this accounts for 37 per cent of the time intervals and so the change is plainly significant. But, as I have already mentioned, the diagram is insensitive to the effects of increasing the frequency of noise bursts from HS2, and this is obviously an important factor in assessing the impact that HS2 would have. If we also take into account the “noisy bird” shortcomings of sound level meter measurements that I pointed out in part 2, then I don’t think that P7494(2) is particularly enlightening.

I don’t feel that Mr Mould’s defence, if a defence is what it was intended to be, that “the key change is going to be the frequency of existing events, which will be towards the lower end of the mid range of the noise levels that already form the existing and separate noise event picture within [the] church” (see footnote 4) is very robust. After all he also told the Select Committee that “we’re going to continue to work closely with the church and others to seek to mitigate at source and at receptor on this” (see footnote 5).

If HS2 Ltd is prepared to consider mitigation “at source and receptor” then you’d better believe that there is a problem, even if the HS2 noise will not “increase the peak noise experience” of audiences trying to concentrate on music being performed in the church.


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