Examination of Witnesses (Questions 3180
- 3199)
3180. That has the capacity, does it not, to
cause greater effect than would be expected with airborne noise
at a similar level? Do you agree?
(Mr Thornely-Taylor) No. The difference between
vibration-free groundborne noise and noise from a lorry passing
in the road is quite small because with closed windows, and I
did make that caveat, by definition as the airspace has been blocked
off sound can only get in your building by vibrating the walls
if it is a lorry going by. The difference is that it is surfaces
that are radiating the noise that are not the same as they are
with a passing lorry. I accept the point made by Mr Methold yesterday
that you are less likely to be able to move to another room if
you want to reduce the noise and that is probably where groundborne
noise can be differentiated from noise from vehicles in the street.
3181. Let us ask the question again and get
a simple answer, please, Mr Thornely-Taylor. Groundborne noise
will cause a greater effect than would be expected from airborne
noise at a similar level, yes or no?
(Mr Thornely-Taylor) I have to say no because
it is not a simple point. If I said yes I would be oversimplifying
it.
3182. Would you have a look at your Crossrail
document, please? I have in front of me the Crossrail Technical
Report volume one of eight. I am not sure what the number is.
(Mr Thornely-Taylor) I know the one.
3183. It is the RPS document.
(Mr Thornely-Taylor) I know it very well.
3184. What I just read to you is a direct quote
from 2.15 which is a document produced by Crossrail. Do you say
no again?[12]
(Mr Thornely-Taylor) I would be
glad to read out what is in that document because it is more or
less the same as I have just been explaining to the Committee.
3185. I just read it out to you. Do you want
to have a look at it?
(Mr Thornely-Taylor) I would prefer that we
read extended passages from it because I have explained in that
document the same concepts that I have just been explaining to
the Committee.
3186. I will read the full sentence: "The
second feature is that at night groundborne noise may reach the
ear without passing through air through the bed and pillow and
causing greater effect than will be expected from airborne noise
at a similar level". Right or wrong?
(Mr Thornely-Taylor) A different question,
not the general point that Mr Clarkson put to me a moment ago.
3187. It was exactly that.
(Mr Thornely-Taylor) I did not agree to the
general proposition that groundborne noise and airborne noise
were essentially different.
3188. Explain how that is wrong on that basis?
(Mr Thornely-Taylor) When the sound comes up
through the pillow it is different because, as I explained a little
while ago, the noise from a passing vehicle in the road, though
it does vibrate the structure, tends to vibrate a different part
of the structure and there would probably be less of that effect
from a lorry than there is from an Underground train.
3189. Let us really try and get this clear.
It is your solemn case, Mr Thornely-Taylor, that it is noise through
the pillow that will cause a greater effect than airborne noise
at a similar level. Seriously?
(Mr Thornely-Taylor) Yes.
3190. Very well. May we proceed on that basis.
The characteristic is that groundborne noise tends to be the same
in all rooms, does it not, subject to a slight reduction or increase
in floor level?
(Mr Thornely-Taylor) Yes,
Mr Clarkson is right. At the same floor level there would not
be much difference as you move around the rooms on that floor
but there is a slight reduction as you move up the building.
3191. Unlike the noisy lorry in the street outside,
I cannot move rooms, can I?
(Mr Thornely-Taylor) That is quite right.
3192. Noise insulation regulations cannot help
me if there is a problem, can they?
(Mr Thornely-Taylor) No, they cannot.
3193. Once it is there it is fixed, is it not?
(Mr Thornely-Taylor) No, it is not fixed because,
quite rightly, you had some evidence yesterday about the importance
of the maintenance regime on the railway, the condition of the
rail surface and the wheels of the train and noise levels do vary
quite considerably over time.
3194. That goes to my next point, and the Committee
has picked this up, that there is a point at which such as wheel
flats and rough rails have the characteristic of deteriorating
groundborne noise, do they not?
(Mr Thornely-Taylor) Yes, they do.
3195. You told us yesterday that many lines
were worse since 1994, is that right?
(Mr Thornely-Taylor) Yes.
3196. So when we design this now we anticipate,
do we not, deterioration?
(Mr Thornely-Taylor) We anticipate a maintenance
regime that will intercept deterioration that takes the roughness
of the rail and the wheels beyond the point that has been assumed
in the moderately pessimistic predictions that have been made.
3197. What specific allowance have you made,
if any, for that deterioration or failure of the maintenance regime?
(Mr Thornely-Taylor) The spectrum of roughness
that is in the model is worse than good spectra that you find
on the railways by a sufficient margin to allow for the fact that
with a maintenance regime there is a starting point when things
are good, there is a deterioration over time and maintenance is
triggered, things drop back to being good and then deteriorate
again. It is a sawtooth shape and the assumption in the modelling
allows for us to be at the top of the sawtooth.
3198. What allowance is that, how many dB(A)?
(Mr Thornely-Taylor) There is actually a large
difference between the assumption in modelling and the roughness
levels you find on very good systems. Five or, in some cases,
as much as 10 dB(A) difference.
3199. So the picture is—I think you said
7 dB(A) yesterday—poor maintenance could increase the groundborne
noise by some 10 dB(A), is that fair?
(Mr Thornely-Taylor) Things can go badly wrong
and it can be as much as 20.
12 Crossrail Ref: P44, Technical Report (UNEWO-STR109-011). Back
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