House of Lords - Crossrail Bill - Minutes of Evidence

Select Committee on the Crossrail Bill Minutes of Evidence

Examination of Witnesses (Questions 180 - 199)

180. LORD BROOKE OF ALVERTHORPE: This can affect people differently depending on their age then?
(Mr Thornely-Taylor) Most certainly. There is a set of curves which can be plotted according to the age of the person. It is a normal progression, as one's age advances, for one's high frequency hearing to diminish.

181. LORD BROOKE OF ALVERTHORPE: So one hears the rumble more as one gets older?
(Mr Thornely-Taylor) Indeed one does. It relatively becomes more prominent. I should say that people report effects well below 20Hz and occasionally you see stories in the press about strange noises in the Bristol area, or strange noises sometimes called "the hum" that when investigated are very hard to measure and yet people distinctly report hearing something. There is in fact a journal devoted specifically to low frequency noise dealing with these very low frequency signals.

182. CHAIRMAN: It is also capable of being directional, is it not, air frequency noise?
(Mr Thornely-Taylor) Most certainly. A particular feature of low frequency noise is that its wave length is very large—several metres—and that means that in a room standing waves are set up much more prominently than happens at higher frequencies, and you can move from a quiet spot to a noisier spot. I have often found in hotel rooms, which frequently have air-conditioning running which can be quite irritating, that merely moving the position of the bed or, on one occasion, I just moved my pillow to the foot of the bed and slept that way round, I was in what is known as an "anti-node" and the noise had gone.

183. MR ELVIN: Mr Thornely-Taylor, to go from the ridiculous to the sublime, if you listen to very low organ notes, for example, you can hear the fluctuation in the noise?
(Mr Thornely-Taylor) I used to have the privilege of being able to play a large organ in a very large hall and it was great fun to play the lowest two notes separated by a semitone, and the beating between them—

184. MR ELVIN:— would make your windows rattle!
(Mr Thornely-Taylor) It is like a motorcycle. I think I have digressed a little!

185. MR ELVIN: Shall we go back to LAeq?
(Mr Thornely-Taylor) Shall we now go onto slide 18 and talk about the characteristics of this LAeq scale, because I mentioned that we needed to cope with varying sound environments.[56] It has these consequences, which all flow from its energy-based nature: it follows automatically that these different kinds of doubling all have the same effect. First of all, I need to expand on the fundamental point we saw in an earlier slide that 10dB is actually concealing a tenfold change in energy. I showed that time-varying environment first with a dB scale and I showed the identical slide with energy units, and they went up by a factor of ten each time there was a 10dB increase. It is interesting to look in slightly more detail at changes of less than ten, and whereas 10dB is a tenfold increase in energy the other important rule of thumb is that 3dB is a doubling of energy. Again that illustrates the different world between physical measures and human perception. I explained that if a sound that was continuously changed by 3dB and there was a time lapse between us hearing the first and the second sound, we would only just about notice the difference at three; but that is for a change where the energy has halved or doubled. It is always the case that a 3dB change means that the energy has halved or doubled. It follows from that if we are using LAeq for measuring environmental train noise and during a time like eight hours twice as many trains go by, and they are the same trains, the LAeq value for that eight hours goes up by three. That is a simple physical relationship. Likewise if only half the number of trains went by the LAeq level would go down by three. In exactly the same way, if the noise went on for twice as long—same number of sources and while the source was there the same sound level—but if its duration was twice as long the sound system would be delivering twice as much energy over that eight hour period to the person listening, likewise the LAeq will change by three. A further permutation is that if you are measuring the noise from some fixed sources, let us say there are two fans running continuously, and we switch on two identical fans the same distance from the listener and thereby we double the number of sources, again the LAeq level, and in fact in that case the overall sound level, will go up by three. This applies always; it is a fundamental mathematical relationship. Moving on to slide 19—

186. CHAIRMAN: Before you leave that, these are not cumulative?
(Mr Thornely-Taylor) It is cumulative. If you do all those things together, if we first of all doubled the energy and the sound (going back to slide 18) the level in LAeq and the overall level would go up by three. If we then switched on twice as many identical sources it would go up by another three—six above where we started. If these were variable events and we doubled the duration of all the events it would go up by another three to nine. If we had twice as many of those events it would go up by yet another three to 12. It goes on all the way up. It is a feature of the decibel scale that it is always telling us proportions; it is never telling you absolute values; so it is just shorthand for saying double the energy—it is easier to say plus 3dB. Each doubling, twofold, fourfold, eightfold, sixteenfold, we have gone up by 12dB. The same happens on slide 19 when we just talk in terms of ten times.[57] It is the same as the previous slide except instead of doubling we are increasing things by a factor of ten. Again it is cumulative. If the sound is due to a source with some variable power setting and you turn the power setting up tenfold, the sound level will go up by 10dB. If you then switch on ten times the number of sources it will go up by another ten, so it will have gone up 20. If it is an intermittent sound pattern over a period of time and those events last for ten times the length it will go up another ten to 30 above where we started. If there are ten times as many events, another ten; so we have gone up 40dB from where we started as a result of those changes, simply because each of those changes is actually delivering ten times more sound energy during the period over which we are calculating the index. These so far have all been physical measurements which have been adjusted to try to match the loudness response of listeners; but we now have to move on to something much more complex, because when people are disturbed by noise they talk not so much in terms of loudness (they may mention that) but they will talk about "annoyance", "sleep disturbance", all sorts of other effects of noise besides just judgment of how loud it is. It is true to say that however good your system of converting sound levels into numbers may be, it has no meaning at all unless you can relate it to how a population of listeners are going to respond to it. Any noise index that we use for environmental assessment, for regulation or for policy-making has to have associated with it the results of social surveys in which you seek to discover how a population responds to noise levels expressed using one index or another. To take aircraft noise as an example being somewhat topical, we used to have something called a noise and number index which was jettisoned in the 1980s in favour of LAeq that I have been talking about; and there have been a series of social surveys, not only at British airports but at international airports around the world, which enable you to say at any particular exposure in terms of LAeq there is a probability of this much that people will be highly annoyed, a probability of that much that they will not be much annoyed at all, and most of the population will fall somewhere in between. On the next slide, slide 20 we see a simplified representation of that kind of information.[58] There have been now many, many social surveys in developed countries and researchers have done what are known at meta-analyses; they have looked at the results of all of them and done their best to collapse them into simple curves. The interesting thing is that they found a different annoyance response according to the nature of the source. These are all about transportation noise sources, which is the most widespread kind of environmental noise. Taking aircraft noise—in fact the unit here is Lden, which is Leq with evening and night given a weighting for the fact that people are more sensitive to noise in the evening and the night, but for the purposes of explanation we can regard it as Leq, for example, if the outdoor noise environment due to aircraft is 55, taking a very large population you would find that ten per cent of the population were highly annoyed. If you move up still sticking with aircraft noise to 61, for example, you would find that 20 per cent of the population were highly annoyed. It follows from that that 80 per cent have another kind of level of annoyance and it is an important feature of all these cases that people vary enormously in their sensitivity to noise. Some will complain at very low levels; some will be completely indifferent to very high levels. The second interesting thing about this chart is that, in these large analyses that find that, annoyance is dependent on the nature of the source: aircraft are the most annoying; road traffic noise is next; and you have to go to between 59 and 60 to get ten per cent highly annoyed; and railways allow 66 before you get ten per cent highly annoyed. There are lots of theories as to why that is, but it is broadly the case. It means that assessments using the LAeq scale produce different answers according to what kind of noise source it is.

187. CHAIRMAN: Is Lden day, evening and night?
(Mr Thornely-Taylor) Indeed, my Lord, that is right.

188. CHAIRMAN: How do you then average it out in order to get a single figure?
(Mr Thornely-Taylor) What you do is at seven o'clock at night you add 5dB to the measured level and you keep on doing that until 11 o'clock at night when you start adding a total of ten to the measured level; and you keep doing that until seven o'clock in the morning when you come back to ordinary LAeq, if I can put it that way. Lden crops up because there is a European Union directive requiring noise mapping, and the unit required for these maps is the Lden system. It has not progressed beyond that point at the present time. At this point, having mentioned the European Union, I will move on to guidelines and standards. Slide 21 lists the standards that we used particularly for this project.[59] The first one is a document which anyone who has spent time in a tribunal dealing with noise will have come across—it always appears. It is called Guidelines for Community Noise, paid for by the World Health Organisation, published by the Ministry of the Environment or the Institute of Environmental Epidemiology in Singapore, and, though not formally adopted by the WHO as a formal WHO document, is loosely called "The WHO Guidelines". It contains a great deal of information. It has a very extensive review of the literature on the effects of noise of all kinds across the whole spectrum from annoyance through to hearing conservation—almost every aspect of the subject.

189. MR ELVIN: What is the date of the guidance, please?
(Mr Thornely-Taylor) The printed version, which is the official version, was printed and published in the year 2000. There are some versions with 1999 on them but, having clarified with the lead author, Professor Bergland, the Singapore-published 2000 edition is the formal publication. In the UK we also have British Standard 8233, which is guidance for the sound insulation and noise reduction for buildings, aimed at people designing buildings. Important, particularly for Crossrail, with all its construction sites, is BS 5228, which gives guidance on noise and vibration control on construction and open sites. Also important for all the plant that I was referring to—tunnel ventilation fans, station plants and depots—is British Standard 4142, the method for rating industrial noise affecting mixed residential and industrial areas, and vibration is addressed in British Standard 6472. In slide 22 we will have a look at those Guidelines for Community Noise which are so widely quoted.[60] They talk about something called the critical health event. Of all the health effects that noise can have, which may range from annoyance to hearing damage to health effects, in any particular case one of those effects is the one that determines the guidance, and that is what they mean by "critical health effects". So, for example, when they are talking about noise levels in outdoor living areas the principal thing to think about is annoyance, and it gives guidance on levels at which various degrees of annoyance occur.

190. MR ELVIN: Mr Thornely-Taylor, just keeping an eye on the clock, can we just highlight the ones that are most significant so far as Crossrail is concerned, please?
(Mr Thornely-Taylor) The most significant one is dwellings, and particularly sleep disturbance, because we will be running trains at night in tunnels underneath people. The guidance is 30 in LAeq terms, and in LAmax terms LAmax fast is 45, although in the text of the document it advises that where there is low-frequency noise lower levels are desirable. The next slide is merely the bottom half of that table, shown for completeness, but we do not need to dwell on it.[61] Slide 24 is the point about 30 dB(A) LAeq for continuous noise.[62] If it is not continuous LAmax is best. It says the effects are observed at 45, or less, noise events. Exceeding 45 should be limited, if possible—even lower for sensitive people—and there is advice that low-frequency noise should be lower as well. It suggests that to prevent sleep disturbance you should consider both LAeq and the number of events. Moving to slide 25, very similar numbers are in British Standard 8233.[63] We do not particularly need to dwell on them: bedrooms, a good standard LAeq 30, reasonable standard LAeq 35. Both in the case of this standard and the WHO table the time period, denoted by a "T" after LAeq, is eight hours for night time. For daytime it will be either the full 16 hours or a shorter period, if that is more appropriate. That is the end of standards for sound. Slide 26: for vibration we use something called the Vibration Dose Value for the kind of vibration that is not heard; it is perceived, technically, through the sense of touch, although that includes movement of the body—whether it is sitting on a vibrating surface, lying on a vibrating surface, standing on a vibrating floor—as opposed to the sense of hearing.[64] We use an index called Vibration Dose Value, instead of a decibel scale. I do not intend to take up time on that subject today. I will just, on slide 27, mention the alternative method of assessing vibration when it is affecting buildings.[65] Clearly, on a construction site, there are two things to be concerned about. If the building is occupied and you are doing a construction activity, you may annoy people in the building as a result of the vibration. However, secondly, if the building is unoccupied, while there is nobody there to annoy, there comes a point, at a very, very much higher level, when you need to be concerned about the effects of vibration on the fabric of the building. For that purpose, Peak Particle Velocity, as it is called, is used. We can now go at a much faster pace because I have finished with the detailed explanations. We can just run through the standards that we use. On slide 28, starting with construction noise, the method used is to compare the LAeq level from the construction work with the level you would have without the construction site and, also, compare it with absolute trigger levels (as they are referred to).[66] These are shown on slide 29.[67] As the daytime ambient (that is the noise) not due to the construction noise becomes greater so the effect of the construction noise becomes less, because, clearly, a construction site in a very noisy locality has less of an impact than a construction site in a very quiet locality. This figure shows the two important levels: the level at which the Crossrail policy for temporary re-housing comes into play, if the provision of noise insulation is not likely to be sufficient, and the level at which the provision of sound insulation applies. The Environmental Statement shows quite extensive likely eligibility for noise insulation.

191. MR ELVIN: Just for the record, the core daytime working period is from eight in the morning till six in the evening, on most work days.
(Mr Thornely-Taylor) That is quite correct, yes. The next slide, 30, just quotes from the Environmental Statement the numbers applied to this Vibration Dose Value that I mentioned.[68] It is very difficult to give them physical meaning, but it does not mean complete imperception about vibration but using British Standard 6472 the probability of people commenting adversely is low at these levels Construction vibration is on slide 31, in terms of the Peak Particle Velocity that I mentioned, and we do not need to dwell on it.[69] Slide 32 takes us to operation, having finished with construction.[70] We look at changes in the LAeq level to see whether the effect of operating the railway is significant or not. The Environmental Statement treats a change of more than three as a significant effect. The magnitude of the increase depends on how much the change is; if it is more than ten, for example, it is treated as a substantial increase. Slide 33, again on surface railway operation, just states the statutory position regarding the provision of noise insulation against the operating railway—again, using the LAeq scale for day.[71] These are external noise levels, 1 metre in front of a fac"ade.

192. CHAIRMAN: So sorry, just a moment. On 32 we have got LAmaxF.
(Mr Thornely-Taylor) There is a footnote about a secondary test. If there is not a pre-existing sequence of train noise events that exceed 85 LAmaxF (for "fast") then should there be a case where Crossrail causes LAmaxF to be more than 85 that is a secondary test for significant effect.

193. MR ELVIN: Going to 34 now.

194. LORD SNAPE: Before you do, Mr Thornely-Taylor, forgive me for interrupting, on 33 you mentioned a figure of 68 decibels of sound insulation alongside a railway line. Could you just tell me and the other Members of the Committee how that figure would equate to houses alongside a motorway or trunk road, or adjacent to an airport?
(Mr Thornely-Taylor) The easiest one to take is the example of houses alongside a motorway or a trunk road. Houses alongside a very busy, multi-laned highway, such as some of the six-/eight-lane highways that go out through the outer areas of London, would be in the 80s—they would be well in excess of 68. The origin of the 68 goes back to the Noise Advisory Council (which decades ago I was a member of), which was asked to state what noise level was the limit of the acceptable for highway noise. It said that 70, using an index called LA10 (which in those days, so long ago, LAeq was not used, and instead the level exceeded for 10 per cent of the time was used), and that has gone through many changes, and has emerged in the relatively recent railway noise insulation regulations as being equivalent to 68 on the LAeq scale by day and 63 at night. In a nutshell, it is the limit of the acceptable, and that is why statutory entitlement to noise insulation kicks in there.

195. LORD SNAPE: That is for the railway. Can I ask you would that be the same level, 68, for roads or airports for sound insulation?
(Mr Thornely-Taylor) Airports have noise insulation schemes which differ from airport to airport, but they tend to be at a lower level than that—not least because we saw that slide earlier showing that people find aircraft more annoying at lower levels.

196. LORD SNAPE: And trains, of course, less intrusive.
(Mr Thornely-Taylor) This one is for trains. The equivalent regulation for highways has the same number, 68, but it still uses the old-fashioned unit of LA10, the level exceeded for 10 per cent of the time. It is physically not quite the same, but when the railway regulations were produced, the Committee that were charged with devising them were specifically instructed to come up with a scheme that was equitable with the scheme for roads.

197. LORD SNAPE: Thank you.
(Mr Thornely-Taylor) May we now move to underground noise and go to slide 34? [72] The convention is to concentrate on the maximum sound level, LAmax,S. We have had at least two major underground railways or railways with significant underground sections constructed in recent decades, namely the Jubilee Line Extension and the Channel Tunnel Rail Link. They both uses LAmax,S as the primary test of the significance of the maximum sound level due to the passage of underground trains. Indeed, in slide 35 we see an extract from the Environmental Statement and we see that if LAmax,S is predicted at 35 to 39 it is on the radar—but it is low.[73] If it is over 40 it is a significant impact, and should it be over 49, for example, a very high impact. In fact, the Jubilee Line Extension, for example, manages to achieve actual LAmax levels well down in the low or even lower region. Moving on to slide 36, there are lots of places in London that are above underground tunnel systems constructed before the Jubilee Line Extension which used a very simple form of rail support, and you can actually stand on the platform of some of them and see it, rails fixed to cast-iron chairs screwed into hardwood blocks set in concrete and the rails have joints in them, as a result of which it is quite common, though it does not always happen, in a house above the Bakerloo Line or the Northern Line, for example, to get maximum noise levels, 40 to 50, and the highest I have ever come across was about 55.[74] Those are bad cases and many people are exposed to lower levels than that.

198. LORD YOUNG OF NORWOOD GREEN: So the Jubilee Line improvement was due to one track design?
(Mr Thornely-Taylor) Yes.

199. What about the rolling stock itself? What was the contribution? I can see from your description of the improvements in track design that it went from pretty crude with what seemed to be little or no attention paid to the transmission of noise and vibration to a much more sophisticated attempt, but how would you divide the fact that they managed to reduce it quite significantly? Would you put it down to, say, 50 or 60 per cent track design and rolling stock? I am just floating some figures.
(Mr Thornely-Taylor) Several things have happened in the railway industry. One of the important ones is the move to disc-braking of vehicles, so you no longer roughen the wheel treads with blocks. Most important is the move to using continuously welded rail in underground systems and universally to use resilient supports for the rail, and in circumstances where you need particularly large reductions in groundborne noise, the entire track system is constructed on concrete blocks themselves supported on rubber bearings known as `floating slab track'.

56 Crossrail Ref: P4, Basics-Noise (LINEWD-RTT01-018) Back

57 Crossrail Ref: P4, Basics-Noise (LINEWD-RTT01-019) Back

58 Crossrail Ref: P4, Comparison of Percentage highly annoyed for different sources (Source: Miedema and Oudshoorn 2001) (LINEWD-RTT01-020) Back

59 Crossrail Ref: P4, Noise and Vibration Guidelines (LINEWD-RTT01-021) Back

60 Crossrail Ref: P4, Guidelines for Community Noise (LINEWD-RTT01-022) Back

61 Crossrail Ref: P4, Guidelines for Community Noise (LINEWD-RTT01-023) Back

62 Crossrail Ref: P4, Guidelines for Community Noise (LINEWD-RTT01-024) Back

63 Crossrail Ref: P4, British Standard 8233 (LINEWD-RTT01-025) Back

64 Crossrail Ref: P4, Basics-Vibration-Affecting People (LINEWD-RTT01-026) Back

65 Crossrail Ref: P4, Basics-Vibration-Affecting Buildings (LINEWD-RTT01-027) Back

66 Crossrail Ref: P4, Standards-Construction noise (LINEWD-RTT01-028) Back

67 Crossrail Ref: P4, Crossrail trigger levels-core daytime working period (LINEWD-RTT01-029) Back