Examination of Witnesses (Questions 3040
- 3059)
3040. When you gave your evidence in chief I
think you cited an example of an LAmax measurement that you had
taken in a bedroom with a train going underneath of 26 dB(A) at
LAmax. Can you tell me where that was?
(Mr Methold) First, it was
not LAmax background; it was the true background noise level,
the underlying noise level that Mr Thornley-Taylor introduced
us to last week, the L90, which strips away events. It was taken
in a bedroom above the North Downs tunnel.
3041. And the noise climate, apart from the
railway, above the North Downs tunnel, is that similar to the
noise climate in central London?
(Mr Methold) In similar
properties it certainly is. We have the A229 running fairly close
to some of these properties. In Kit's Coty I measured a level
of 58.5 dB outside one of those properties.
3042. The next point I want to turn to is my
reference to documents that are set out at tab E in the bundle
that I have put in and that Mr Thornley-Taylor will speak to,
the front page of which reads "Guidelines for Community Noise".
If we turn in this document to page 65 we can see a table 4.1
which sets out certain guideline values for community noise in
specific environments.[6]
I want to draw the Committee's attention to the right hand column
of that table, which is headed LAmax Fast, and we need to know
that it is fast rather than slow. If we go down we come to a 45,
which is a guideline value for community noise as an LAmax Fast
for sleep disturbance at night inside bedrooms.
(Mr Methold) Correct.
3043. Again, if we keep going down we come to
another 45, which is a sleep disturbance guideline value for pre-school
bedrooms and indoors. That is to apply to sleeping toddlers during
the day. We can keep going down and there is a 40 in that same
column, hospital ward rooms indoors, sleep disturbance at night
time, again a 40 LAmax Fast level is indicated. I put it to you
that none of those levels set out in this document supports the
adoption of 35 dB(A) LAmax as a threshold for protecting people
from sleep disturbance, does it?
(Mr Methold) The World Health
Organisation document does not anywhere refer to groundborne noise
and again I refer you back to the technical evidence I gave earlier
which was making specifically the point that this is a very unusual,
low frequency type of noise. In fact, the World Health Organisation
is very careful on several occasions in its document to point
out that we should treat low frequency events very differently
from other community noise types of source. Noise with low frequency
components require lower guideline levels—and I am quoting
from the document here—and in intermittent noise it is emphasised
that it is necessary to take into account both the maximum sound
pressure and the number of noise events.
3044. Coming to the number of noise events,
obviously, the LAmax threshold is a particular threshold which
does not take into account noise over a continuous period of time,
but the LAeq does, does it not?
(Mr Methold) It does.
3045. We can see from table 4.1, for example,
in the row headed "Dwelling Indoors", inside bedroom
sleep disturbance night time we can see 30 LAeq dB is identified
and the time base of eight hours, that being the eight hours of
the night time.
(Mr Methold) Yes.
3046. If we turn on to tab F there is a note
that Mr Thornley-Taylor has prepared in which he has set out a
calculation of what an LAmax level of 40 equates to in terms of
the eight hour LAeq having regard to the number of trains that
would operate in particular hours. I am not going to take the
Committee to the rather frightening formula on page four, but
I will take the Committee to the conclusion of that document in
paragraph 1.6 on page 5 where Mr Thornley-Taylor concludes, "Thus,
the 40 dB LAmax is equivalent to less than 22 dB LAeq where T
is eight hours".[7]
Do you see that conclusion?
(Mr Methold) Yes, I do.
3047. I think you have had an opportunity to
look at this particular note. The calculation set out there is
correct, is it not?
(Mr Methold) It is.
3048. And so the conclusion must be that by
reference to the guidelines for community noise level that takes
into account the frequency of events, the 40 dB LAmax level provides
a significant margin of protection compared to those guideline
values, does it not?
(Mr Methold) We need to
be very clear about what that 30 dB LAeq is based upon and again
the WHO document is very clear: it refers to sleep disturbance
due to continuous background noise and I reject the suggestion
that a noise event from a train passing underneath a building
is a continuous background noise source.
3049. The 40 dB LAmax criterion has been adopted
as a design criterion for CTRL; is that correct?
(Mr Methold) Yes.
3050. For Thameslink 2000?
(Mr Methold) Yes.
3051. For the Jubilee line extension?
(Mr Methold) Yes.
3052. And for the Docklands Light Railway; is
that also right?
(Mr Methold) Correct.
3053. In relation to the Jubilee line extension
are you aware of any recorded complaints or records of annoyance
arising from the operation of that line?
(Mr Methold) I am not aware
of any.
3054. You referred in your evidence in chief
to design guidelines presented by APTA, the American Public Transit
Association; is that right?
(Mr Methold) Yes.
3055. Am I right in saying that the thresholds
identified in that document are not based upon any specific dose
response research?
(Mr Methold) That is my
understanding.
3056. So they are policies rather than related
to any particular level of environmental noise deemed to be acceptable?
(Mr Methold) In the absence
of any dose response curve for this type of noise; that is correct.
3057. And the same is true, is it not, of the
FTA criteria that you also produced?
(Mr Methold) That is correct.
3058. With regard to the policy documents that
you referred to, Camden UDP and the supplementary planning guidance,
I think I am right in saying that none of those documents provides
any reference to being based upon any particular dose response
research?
(Mr Methold) That is correct.
3059. Again, they are in the same categories,
the APTA and the FTA; they are policy led?
(Mr Methold) They are based
upon the best practice that is advocated by APTA and the FTA documents.
6 Crossrail Ref: P43, World Health Organisation, Guidelines
for Community Noise, p65, Table 4.1 Guideline values for community
noise in specific environments (CAMDLB-31904-029). Back
7
Crossrail Ref: P44, Crossrail groundborne noise LAmax and LAeq,
2 February 2006 (CAMDLB-31904-037). Back
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