Examination of Witnesses (Questions 20760
- 20779)
20760. Mr Binley: Would you do that then,
please, Lady Bright.
20761. Lady Bright: It should have come
up earlier and, because of the technical problems, it did not.[21]
It says:
20762. "Dear Margot, First of all, I would
like to thank you for our visit yesterday. I would have to say
that, from a noise perspective, the potential scheme at Westbourne
Park Villas is both a very interesting one and acoustically of
clear benefit.
20763. "The existing wall—The primary
issue is whether the 2.75-metre-high existing wall is capable
of supporting the increased load of a noise barrier structure
attached to the top. Certainly a structural engineer or a competent
noise barrier installer would be able to confirm the integrity
of a design. However, from first examination, we believe that
even a low barrier system would provide a perceptible reduction
in noise and it therefore should be considered as a viable option.
20764. "Potential noise reduction—It
is apparent that a suitable noise study has not been carried out.
As such, an informed judgment has not been presented as to whether
a noise barrier would be of benefit. In our opinion, it should
therefore be pursued. We have carried out an indicative examination
of the location taking into account the existing wall, the position
of the houses in Westbourne Park Villas, the basic topography
and spread of rail tracks. From this we have deduced an estimate
for the performance of barriers of differing heights."
20765. These are that the potential noise reduction
from the ground floor façade with a one-metre barrier is
two decibels, a two-metre barrier of four decibels, a three-metre
barrier, six. From the first-floor level, a one-metre barrier
would be three decibels, a two-metre barrier, five decibels, and
a three-metre barrier, seven. For the second-floor façade,
it would be a three-decibel reduction with a one-metre barrier,
six decibels with a two-metre barrier, and nine with a three-metre
barrier. It goes on:
20766. "This has assumed that the barrier
has been installed to rest on top of the existing wall and that
the barrier is absorptive in design. We would recommend that it
is absorptive on both sides to reduce back reflections from the
houses in Westbourne Park Villas. Normally, a 3dB drop in noise
is regarded as not only perceptible but retainable. In other words,
the noise reduction is noticed immediately and at a later stage.
With this in mind, we would expect even a 1-metre-high absorptive
barrier to give a moderate reduction in noise. The added load
of a 1-metre high barrier would not be too onerous.
20767. "We would expect a 3-metre-high
absorptive barrier to give a substantial reduction in noise at
ground, first and second floor. This would clearly make a large
difference to the quality of life for residents in Westbourne
Park Villas. Our concern would be regarding the capability of
the wall to support such a structure. Once again, we would emphasise
that this is not our field and that it is a question to be put
to a suitable structural engineer. However, Crossrail have confirmed
that the wall is solid and well constructed in the environmental
statement.
20768. "We would therefore view a 2-metre-high
absorptive barrier as a possible compromise that still is expected
to give a healthy reduction in noise.
20769. "Dimensions and Costs—We estimated
the span between wall pillars to be about 4 metres. There are
about 90 spans between the two rail bridges giving an estimated
overall length of 360 metres. Assuming normal ground conditions,
the cost of supplying and installing a 2-metre, high-performance,
absorptive noise barrier would be in the region of £250 per
linear metre. This would make the total cost of such a system
to be only £90,000. This gives an indication of the order
of magnitude of cost since the existing wall would most likely
make the installation more complex.
20770. "This estimate is based on the installation
of a typical zero maintenance metal absorptive noise barrier system
similar to the Van Campen design."
20771. I think perhaps I do not need to read
the bit where they are offering to do a detailed study. Thank
you very much for your patience on that. It was supposed to go
with some photographs of which are quite unlike the sort which
you will have seen Network Rail erecting, solid pieces of timber,
on the West Coast Main Line. Is it possible to show those photographs
or not?
20772. Mr Binley: Do you think it will
help us?
20773. Lady Bright: Yes, if you have
not seen any, because you will not have seen barriers like this
much in the UK, certainly not in railway settings.
20774. Mr Binley: Are they included in
this portfolio of photographs?
20775. Lady Bright: There is only one
at the end.[22]
20776. Mr Binley: I think members of
the Committee are okay with this. Any concerns? No, I think we
are okay.
20777. Lady Bright: You have seen enough
barriers.
20778. Mr Binley: Before we move on and
thereafter you might cross-examine Mr Thornely-Taylor, can I just
for the record state that the letter which you have just read
out will be entered into the record as A237.
20779. Ms Lieven: Sir, perhaps I could
just ask Mr Thornely-Taylor for his comments on that letter.
21 Committee Ref: A237, Correspondence from Sound
Barrier Systems to Lady Bright, Environmental Noise Barrier Design
for Westbourne Park Villas (WESTCC-AP2-10-05-001 and -002). Back
22
Committee Ref: A236, Example of an absorptive noise barrier (WESTCC-AP2-10-05-003). Back
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