Examination of Witnesses (Questions 5660
- 5679)
5660. Mr Thornely-Taylor, the Promoter is putting
in a different sort of track system in certain areas of London
specifically to achieve lower expected noise levels.
(Mr Thornely-Taylor) That is quite correct.
5661. It can be done and it could be done in
order to ensure that the levels are lower than the existing background
noise levels in, for example, residential properties in Spitalfields?
(Mr Thornely-Taylor) Yes, I am sure there
are many things that would be nice to have on a system such as
this, but the correct approach to designing a major project such
as this is to select appropriate design objectives, the ones that
are reasonably required and could be achieved at a cost which
does not add to the many other additional costs that arise when
detailed design progresses in a project such as this. It would
be nice to give everybody everything that was feasible in theory,
but the correct engineering approach is to choose the right objective
and to use the most cost-effective value engineered method of
achieving it.
5662. Mr Thornely-Taylor, it may be you cannot
answer this question, but do you know how much it would cost to
put in those enhanced track features in that short section of
Spitalfields?
(Mr Thornely-Taylor) I have not looked
at the cost of a short section in Spitalfields. I think it would
be unlikely that a requirement for one group of residents would
be imposed different from another group of residents.
5663. MS JONES: Thank you very much.
I have no further questions.
5664. LORD SNAPE: Earlier in Ms Jones's
opening statement, Mr Thornely-Taylor, she implied—and I
paraphrase it—that because this would be a fairly busy railway
line during the hours when the trains were running there would
almost continuous noise from the tunnel. Is she right in implying
that?
(Mr Thornely-Taylor)
No, my Lord, it is not like that. It will take a Crossrail train
seven to ten seconds to pass, depending on specific location and
its speed, and on 24 trains per hour that means frequent passages
but it is nothing like continuous.
5665. You mentioned your expertise in airports,
motorways and railways. In your experience, is the noise from
a busy road or a motorway more obtrusive to local residents than
the noise of an "occasional" passing train?
(Mr Thornely-Taylor) Yes, when one is
planning a new motorway or a new airport there are hundreds, if
not thousands, of people normally predicted as receiving noise
levels high enough to require sound insulation. I am not saying
sound insulation is possible for underground noise but it is quite
normal, in an Environmental Statement for an infrastructure project
of that kind, for there to be large numbers of significant residual
impacts.
5666. BARONESS FOOKES: I believe you
have had associations with the Jubilee Line.
(Mr Thornely-Taylor)
Yes, my Lady.
5667. Do we have, to your knowledge, any complaints
about noise from any part of the Jubilee Line from residents or
businesses or anybody else associated with it?
(Mr Thornely-Taylor) None to my knowledge,
my Lady.
5668. The kind of engineering that was put forward
for the Jubilee Line: would what is going to happen with the Crossrail
line be as good as?
(Mr Thornely-Taylor) It will certainly
be as good as and, as I mentioned a little while earlier, we are
expecting the rail support to be of even lower stiffness than
was used in the Jubilee Line, with the result that the levels
of groundborne noise, if there were like for like situations,
would be slightly better.
5669. BARONESS FOOKES: Thank you.
5670. LORD JAMES OF BLACKHEATH: Mr Thornely-Taylor,
during the site visit we experienced nine trains in the 22 minutes
we were there and we had additionally one helicopter coming through.
Do you have the record of what the sound level of that helicopter
was in comparison?
(Mr Thornely-Taylor)
The level I was reading out from the meter (but it was not the
objective of the visit to measure them) was in the mid-30s, my
Lord.
5671. I thought it was a useful comparison with
a different directional sound and, also, a different type of sound—it
was more akin to a vibration noise, as opposed to a steady noise.
(Mr Thornely-Taylor) Helicopter noise
is indeed different—
5672. More intrusive.
(Mr Thornely-Taylor)—and, for some
people, more intrusive, yes, my Lord.
5673. The point I would be making, for Ms Jones's
benefit, is that it was more intrusive because of the nature of
the sound compared to the steady but less intrusive noise of the
trains.
(Mr Thornely-Taylor) I think that is correct,
my Lord.
5674. LORD BROOKE OF ALVETHORPE: How
would you decide who should get the floating track slab and who
should not?
(Mr Thornely-Taylor) The approach is set out in information
paper D10. The first thing is to identify all the special buildings,
such as those listed in the table which we briefly looked at—it
is Table 1 on page 2 of the information paper.[8]
The first thing is to make sure that all the buildings that fall
into any of those categories are identified. Most of them we do
know about; many of them have petitioned the Bill in this or the
other House. The contractor is then required to select a basic
track form that will achieve as many of those without any further
additional measures, but there will undoubtedly be some locations
where an enhanced track form is needed, either to achieve the
more demanding of those figures, such as 25 dB LAMax,s. If I could
clarify whether it is A or L, as we can see it is actually both;
the full description is 25 dB LAMax,s. Those are demanding requirements
and it is almost certain that floating track slab will be needed
in locations where those buildings occur, to ensure that those
levels are achieved. Additionally, the House of Commons' Committee
on the Crossrail Bill asked, as we have heard previously, that
in any case where there is residential accommodation less than
15 metres above the tunnel, floating track slab or an equivalent
better track form should be installed. So those are the two tests,
coupled with the fact that, for the reasons that I have just explained,
we have clear commitments in specific cases such as the Barbican
Hall to put in a specific kind of floating slab to protect its
special environment.
5675. What depth is the tunnel here in Spitalfields?
(Mr Thornely-Taylor) In Spitalfields the
approximate depth is 23 metres. It depends exactly where you are
because the tunnel is rising as you move through the area. It
is more—substantially more—than the 15 metres.
5676. Can we get an idea of what the percentage
difference between the standard track and the floating slab is?
Is it 10 per cent, 15 per cent, 20 per cent, 30 per cent?
(Mr Thornely-Taylor) There are two things
to consider: one is if there is a defined length of floating slab
that has gone in for the purpose of meeting the requirement in
a single building. That will clearly be a finite length of slab,
and the noise that will determine what you hear in the building,
or a large part of it, is what comes from the standard track beyond
the ends of the floating slab. So you would just choose sufficient
length of floating slab to meet the target that you are reaching.
If you had an infinite length of floating slab or portal-to-portal
floating slab, that would give you a greater improvement, but
as a broad rule of thumb, the order of 12 to 15 dBA improvement,
compared with the standard track form, would be a safe assumption,
and that is more than a halving of the loudness of the passage
of trains.
5677. I was looking to see the cost difference
between the two.
(Mr Thornely-Taylor) The cost difference
has become quite complex, since parts of the tunnel will require
floating slab to satisfy the requirement of the House of Commons
Special Report and the emerging studies that we carry out for
specific buildings, such as Christ Church Spitalfields, as we
have just seen. So as of today there is not an up-to-date figure
for the extra cost. The broad rule of thumb that I always give
to clients is that floating track slab approximately doubles the
cost of standard track form.
5678. Approximately double?
(Mr Thornely-Taylor) Yes.
5679. I did make the suggestion when we went
on the site visit that you ought to endeavour to record it, if
possible, so that everybody could have the experience that we
had, and you said that that would be extraordinarily difficult.
I was very impressed with the exercise and was surprised to find
that the sound was so low. Is there any way in which people who
continue to have doubts and question whether they are right or
wrong could find some access to have the experience we had?
(Mr Thornely-Taylor) In theory of course
it can be done, my Lord. It is not as easy as it might seem because
one of the most kind things which the hotel did for us was to
arrange to switch off the fresh air supply to the whole of that
floor. I do not know whether they had complaints from other hotel
residents. It was a combination of that and switching off the
local air-conditioning that gave us those very special circumstances.
I, personally, would hesitate to ask that favour, but of course
it is physically possible. It is not so easy to find another location.
That must have been something like the 30th or 40th place I had
been to looking for good conditions, and it would be quite difficult
to replicate, my Lord.
8 Crossrail Information Paper D10-Groundborne Noise
and Vibration, http://billdocuments.crossrail.co.uk
(LINEWD-IPD10-003) Back
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