Examination of Witnesses (Questions 3320
- 3339)
3320. Exactly.
(Mr Thornely-Taylor) There will be specification
documents which are always voluminous against which the tender
bid will be prepared and eventually the contract administered.
3321. One of the inevitable criteria for that
tender is cost, do you agree?
(Mr Thornely-Taylor) Yes.
3322. What is your evidence as to how you have
assessed it? Have you assessed it, as we understood it yesterday,
with a 5 dB(A) range either side, margin of confidence?
(Mr Thornely-Taylor) I explained yesterday
that the predictions shown in the specialist expert report have
five added to them to account for the known upper band of uncertainty
associated with the prediction process that we use.
3323. When we see 40 dB(A), is that 35 plus
5 therefore?
(Mr Thornely-Taylor) Going back to the point
I made—I think you corrected me I have been talking about
Day Seven but it should have been Day Eight—when I made
my presentation where I explained the approach that had been taken,
40 is the predicted figure. What came out of the computer was
35 to which was added an allowance for uncertainty.
3324. Are you any different than the North Downs
tunnel where the range of predictions in fact prevented environmental
health officers taking it any further because the range of prediction
had uncertainties built into it?
(Mr Thornely-Taylor) I explained yesterday
that the nature of the Union Railways or the CTRL prediction method
was that the 95 per cent confidence band lay 8 or 9 dB either
side of the central prediction. So a prediction of 40 would produce
some at 48 and some at 32. I understand Union Railways considered
that having predicted an average of 40 the obligation had been
met. Our approach in Crossrail is different. There is a clear
obligation to be placed on the nominated undertaker to achieve
40 which means he must include uncertainty.
3325. Where is that as a clear requirement?
(Mr Thornely-Taylor) The clear requirement
is in D10, information paper.
3326. D10, 2.9, is that what you have in mind?
(Mr Thornely-Taylor) "The nominated undertaker
will be required to design the permanent track support system
so that the level of groundborne noise near the centre of any
noise-sensitive room ..." We have incorporated an improvement
over what was in the Environmental Statement because we are no
longer restricting ourselves to the ground floor. This is in any
noise-sensitive room.
3327. Yes. "... is predicted in all reasonably
foreseeable circumstances...".
(Mr Thornely-Taylor) It is the "reasonably
foreseeable circumstances ..." which is a legalese way of
talking about the statistical uncertainty.
3328. There it is at 40. I am the environmental
health officer in five or 10 years' time, I see it is 40, and
you have just told us that the statistical uncertainty allows
the undertakers to aim off and go above 40. That is inevitable,
is it not, exactly the same as CTRL?
(Mr Thornely-Taylor) Precisely the opposite
of the CTRL, the nominated undertaker has to predict in all reasonably
foreseeable circumstances and has to take account of the tail
of the distribution that takes you to the edges of the 95 per
cent confidence band.
3329. Has anybody said that the CTRL was designed
deliberately over 40?
(Mr Thornely-Taylor) I gave extensive evidence
to Members of this House explaining that the nature of the CTRL
prediction model was that you could use it—I used to use
the phrase—epidemiologically. You could look at the effect
for a long length of railway and while it would be inaccurate
to predict the noise effect of any individual building, if you
were interested in aggregating the number of properties—40,
45 or so on—because of its statistical nature you would
get an accurate figure. But it is agreed between me and my opposite
number on CTRL, we both use different approaches but it is agreed
that for specific buildings the CTRL approach is not accurate
and even for small groups of buildings it accuracy is poor which
is why we have the North Downs tunnel problem.
3330. Let us get it quite clear, was the North
Downs tunnel deliberately built to have a regime over 40 dB(A)?
(Mr Thornely-Taylor) The North Downs tunnel
was deliberately built with a location using the method that was
put forward in Parliament and found acceptable. That aimed at
40 dB(A) as the predicted level in the sure and certain knowledge
that there would be some cases above and below it.
3331. Mr Clarkson: That is exactly the
same for the engineer's brief for Crossrail, that they will design
it up to 40 dB(A) and in the sure circumstances, whatever you
have just said, read or otherwise and all reasonable foreseeable
circumstances, there may be some unforeseeable that will take
it apart?
(Mr Thornely-Taylor) It is the precise opposite
of that.
3332. That is what you say but you are not going
to be person who will design it?
(Mr Thornely-Taylor) I might do.
3333. Let us end with this on the design. What
sanction does the Committee have to stop the designers designing
their railway up to 40?
(Mr Thornely-Taylor) I believe the Committee
will obtain the same meaning from paragraph 2.9 that I do and
if they do not, I will invite them to indicate so because information
paper D9, I understand, has a status of undertake in Parliament.
That is not for me to say, it is for Counsel to elaborate on.
I believe what is stated here will happen and if it does not,
the procedures which were available for dealing with briefs undertaking
in Parliament would come into play.
3334. If the undertaking at 40 was changed to
35, there would be an allowance for statistical range, would there
not?
(Mr Thornely-Taylor) Yes.
3335. There would be inbuilt allowance for maintenance?
(Mr Thornely-Taylor) Yes.
3336. What is wrong with it?
(Mr Thornely-Taylor) It is going to cost more,
it is going to introduce design uncertainty for the reasons I
explained yesterday about the difference between the simple purchase
of base plates and its skilled design work required.
3337. It is cost?
(Mr Thornely-Taylor) It is design risk. All
risk can be converted into cost. Most things can be put into cost.
It is not in the estimates that we have been discussing.
3338. That is all I have. Thank you very much.
Re-examined by Mr Taylor
3339. Mr Taylor: Mr Thornely-Taylor,
you were asked questions about the guidelines of community noise
and the point was put that the document is not a document of WHO
policy, which you agreed with. You were also put some questions
about the relevance of the APTA and the FTA documents that have
been presented to the Committee. I want to explore the differences
between the APTA and the FTA document and the difference with
the guidelines of the community noise document. What is the scientific
basis for threshold levels set out in the APTA and the FTA document?
(Mr Thornely-Taylor) I think the
scientific basis is weak. They are not based on dose response
research so much as the experience of views of the authors of
the document with some information from the field, but nothing
of the kind we would like.
| 
