Examination of Witnesses (Questions 7200
- 7219)
7200. Forgive me, I was concerned with the situation
of just looking at it from the point of view we have seen how,
in a large number of cases, even including the ventilation shafts,
L90-5 can be achieved. One possibility would be to have, would
it not, L90-5 as the requirement as per Thameslink with the option
that if it could not be achieved one was required to use best
practicable means?
(Mr Thornely-Taylor) No, I recommend against
that because that has got no upper limit to it. We could end up
with complaints about tunnelling plans, which we certainly do
not want to do.
7201. So the difference, therefore, potentially,
that can be recorded is this: you are suggesting L90+5 for everything.
Yes?
(Mr Thornely-Taylor) Yes.
7202. Against L90-5 over the opportunity to
use best practicable means if one could not achieve that.
(Mr Thornely-Taylor) That is right. That is
it in a nutshell. The latter option has no top limit.
7203. The top limit is required, or demanded
by, the requirement that one uses best practicable means?
(Mr Thornely-Taylor) No, it is not. That could
hypothetically be any number. What Crossrail has done is determined
now that it is possible, and a lot of effort has gone into determining
that it is possible, to achieve L90+5 and making that an overriding
limit. I think that is a far better approach than the local authorities
approach.
7204. Help me with one further matter on this,
please. If, as you say, L90 +5 can be achieved in all cases—yes?
(Mr Thornely-Taylor) Yes.
7205. Then L90-5 together with best practicable
means, if one cannot achieve that, is not ever, is it, going to
go over L90+5? Yes?
(Mr Thornely-Taylor) That is correct.
7206. So the position is that one would have
achieved what was achieved in Thameslink and would be within what
you say is beneficial outside the limit of L90+5.
(Mr Thornely-Taylor) No, because it is coupled
with the best practicable means caveat.
7207. We have seen how that operates. I do not
need to repeat that. Can we just tidy up one or two matters, please?
Questions of cost I can leave over to a note. I would like to
ask you one or two questions, if you do not mind, by reference
to the modal value approach. Could you take LBH40?[91]
Here it is right, is it not, that correctly is recorded or shown,
in relation to the one illustration, the approach which was followed
in working out the background noise?
(Mr Thornely-Taylor) No, we were
led to believe this was the basis of the environmental assessment,
which is not true. The environmental assessment was carried out
on the basis that the significance criterion would be through
LA90+5 and that we have satisfied ourselves that certain mitigation
was available to achieve that, as a consequence of which there
will be no significant effect from the operation of tunnel vent
fans. The material to which large parts of Mr Methold's evidence
were devoted about background level and mode comes from subsequent
information which was shared with local authorities when Crossrail
was looking at a lot of "what-ifs" in further analysis
of the design process for fixed plant. It is not part of the Environmental
Statement.
7208. We can take it shortly, it would appear,
because you agree, do you not, that it would be an incorrect way
to determine using the modal value of the L90?
(Mr Thornely-Taylor) No, I do not, I recommended
it. The reason is that when interpreting BS4142 in a formal way
you have to apply mechanisms that give effect to the words in
a mechanistic fashion, and when the words talk about measuring
background noise that is typical, or which is representative,
the best mathematical way of doing that is to find the level which
occurs most frequently, on the basis that if an environmental
health officer should go out to investigate a complaint the most
probable number he will get on his noise meter is the most frequently
occurring one, and that is the mode. It is not nearly as bad an
indicator as appears from the six case example in LBH39 because
you have hundreds of numbers from which to determine the mode.[92]
It is a very good way of turning semantics into numbers. The issue
I think which Mr Mehtold was getting at is that the mode has been
applied over a period over which noise levels are falling and
he shows that other measures such as mean might be better, and
I understood his evidence to be that he favoured the minimum,
but there is actually no such thing as the minimum because you
have to define the number of times you go out and measure. Both
Havering and Crossrail know that if you go out twice to measure
you get different answers, because we did that; Havering asked
us to do it and a repeat measurement was done. So what is the
minimum? Is it what you get on one occasion, two occasions, three
occasions, or over a year's continuous monitoring? There is no
such thing, really. You have to take a determinable metric that
two people would get the same answer from the same set of numbers,
and the mode is good for that. But it is of no relevance for present
purposes because we are here considering what the noise levels
of the vent fans will be when they are designed in the future.
As Mr Methold I think agreed in cross-examination, this will be
for the local authorities to determine in conjunction with the
nominated undertaker's contractor, according to BS4142, which
may well not be the 1997 version by then. Whatever it says about
how you determine the background is how it will be done. We do
not need to take up time now about whether modal value is right
or not because it plays no part in the outcome of the matters
we are considering.
7209. But whatever happens, therefore, if there
is going to be a new BS4142, you would say that it must make absolutely
plain that one is using the mean, mode or some other definition,
because one can have a very wide variation depending on which
statistic one uses.
(Mr Thornely-Taylor) Indeed, and each contractor
will, as part of the general consultation process, discuss with
the local authority the appropriate way of settling on what the
L90 is. It was not difficult for the Jubilee Line Extension, I
do not see it being difficult for Crossrail.
7210. Plainly, all these matters will have to
be borne in mind. Would you have a look at LBH41, please.[93]
The penultimate bullet point is that this approach is not being
used as in other recent projects.
(Mr Thornely-Taylor) It has not been used on
Crossrail. I have explained that it was not used in the environmental
assessment process.
7211. In the Environmental Statement process,
what was used for the L90?
(Mr Thornely-Taylor) Forgive me, I need to
repeat myself—I do not know whether I should. The Environmental
Statement took the significance threshold of LA90+5, checked that
certain mitigation was available to achieve that, and came to
the conclusion that there would be no significant effect from
the operation of tunnel vent fans. That is how it was done.
7212. Forgive me, you must have identified some
figure for the LA90?
(Mr Thornely-Taylor) No, it was not necessary.
It was a similar approach that was used for groundborne noise
of setting a significance threshold, determining that engineering
means were available at affordable cost to meet it, and coming
to the conclusion that there would be no significant effect—which
is what is required of an Environmental Statement.
7213. On that basis, whatever the LA90 was,
you were saying, "Well, we can work LA90+5 and be all right".
(Mr Thornely-Taylor) Yes. And it was very important
that we established that it would be.
7214. Even if the LA90 happens to be particularly
low, you are all right.
(Mr Thornely-Taylor) Yes.
7215. You can achieve that. Very well, I can
leave that matter there. I think you are going to provide some
information about complaints as to the Jubilee Line?
(Mr Thornely-Taylor) We will inquire of the
environmental health departments of Lambeth and Southwark and
Tower Hamlets, and check whether they have any complaints.
7216. What about London Underground Ltd itself?
(Mr Thornely-Taylor) We will also do that.
7217. Thank you. Is every single phone call
which is ever made to London Underground in respect of noise complaint
or a public transport operator logged?
(Mr Thornely-Taylor) I cannot speak for them.
It is usual for modern methods of complaint handling that that
happens, but I cannot speak for them.
Mr Straker: Thank you very much, sir.
Re-examined by Mr Taylor
7218. Mr Thornely-Taylor, you were asked some
questions, having been taken to the Foreword of BS4142. I think
the hint was that BS4142 should not be used as a basis for assessing
significance. What approach to the assessment of significance
of noise from fixed installations is advocated in PPG24?
(Mr Thornely-Taylor) The use of BS4142.
7219. In relation to assessing the significance
of noise changes in relation to fixed installations, are you aware
of any other British Standard or indeed any other standard that
is used in the UK?
(Mr Thornely-Taylor) There are other standards
relating to determining noise levels, but there is no other standard
for assessing significance.
91 Committee Ref: A81, Analysis of Modal Value-30
Hyde Park Gardens (HAVGLB-14705-040). Back
92
Committee Ref: A81, What has the Promoter done? (HAVGLB-14705-039). Back
93
Committee Ref: A81, Why is this wrong? (HAVGLB-14705-041). Back
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