road traffic noise—its nuisance value

ROAD TRAFFIC NOISE-ITS NUISANCE VALUE

C. G. Fkn-ro~ and D. J. CROOME

Loughborough University of Technology, Leics. (Great Britain)

(Received: 5 June, 1969)

SUMMARY

Methods of measuring the nuisance value of noise, in particular TNI are discussed. Diferent investigators have used various terms, e.g. annoyance, dissatisfaction, loudness, etc., when measuring the psychological effects of noise. It is proposed that the overall subjective eflect of noise may be a combination of these and other factors; this would account for the unsuccessful attempts of most previous work to find a high correlation between an individual score on a psychological scale and physical noise measurements.

A methodology for finding high correlations is suggested in a plan of research to be conducted at Loughborough University.

INTRODUCTION

It seems certain that road traffic noise is detrimental to the life of the human being, but when one is asked for what form this detriment takes an intelligent answer does not spring to mind easily. Terms such as ‘nuisance’, ‘annoyance’ and ‘lossof amenity’ can be used, but the definition and quantification of these terms in psychological language is a formidable task. In this paper nuisance is used to denote the integral effects of annoyance, an emotive reaction, and disturbance which is an interference with living that may or may not cause annoyance. These factors are discussed in the section entitled ‘The Psychological Measure’. The next step must be themonetary costing of these constructs and this would seem impossible using the precise language of science, and exceedingly difficult using the less precise language of town planners and councillors. The physical characteristics of noise radiating from individual vehicles and streams of traffic have been fairly well

Applied Acousrics (2) (1969)--O Elsevier Publishing Company Ltd. England-Printed in Great Britain

280 C. G. BOTTOM, D. J. CROOME

documented and the important parameters isolated. The decay of noise with distance has been investigated as also has, to a certain extent, the shielding effects of barriers, traffic densities, gradients, composition of traffic, and methods of silencing individual vehicles. ~ - 3 However, much work still remains to be conducted into the effects of barriers, adverse weather conditions and the decay of noise with height and over different terrains.

What appears to have been overlooked, however, is the fact that noise levels and sound patterns are only important when considered with respect to observers. This is not strictly true since the noise may be the cause or effect of some vibration which reduces the efficiency of the vehicle or causes damaging vibrations in nearby structures. Little work has been conducted on the effect of noise on drivers and it seems likely that any problems here will be solved by engineers building quieter cars before it is rigorously investigated. Recent Israeli work shows the drivers of diesel trucks to have slower reaction times than drivers of similar petrol engined trucks after the same period of driving. The noise level in the cabs of commercial vehicles is high enough to interfere severely with speech and in some cases high enough to cause mild physiological damage. 4

Why the effects of road traffic noise on people have not been studied above a superficial level is not clear; it could be because of chance factors, because the problem has many practical difficulties, because the benefit is difficult to express in terms of cost, because the study is an inter-disciplinary one, or several other reasons.

Road traffic noise affects people in every type of environment. The authors are particularly interested in the auditory scene in offices and in housing areas; the first study, however, will be concerned with the latter as this is considered the most pressing problem. The methodology to be adopted consists of five stages:

(i) to establish if a nuisance exists; if so, to find the extent and type of nuisance by open-ended interviews;

(ii) to construct a psychological measure of the nuisance which can be administered either by postal questionnaire or by an interviewer;

(iii) to find the physical parameters of the noise which correlate highly with the psychological scale;

(iv) to suggests levels of nuisance which are acceptable to the community; (v) to advocate an economic design for siting buildings near roadways.

THE PROBLEM

Very little is known about the effects of road traffic noise on the community; indeed, the effect of a controlled noise on an individual under experimental conditions is far from certain although numerous articles have appeared on this subject

R O A D TRAFFIC N O I S E - - I T S NUISANCE VALUE 281

in experimental psychology journals; on the whole these are contradictory and no clear overall conclusions can be drawn. 5 A community can behave very differently from the individuals that compose it, due to the complex interactions between its members and also due to particular characteristics of certain members of that community. The term 'community response' is often used when speaking about the effect of noise on a community. We do not feel, however, that this is a meaning- ful term when used with respect to road traffic noise, as the term implies a well- organised group that consults solicitors and acousticians about their dilemma; this rarely happens in the case of road traffic noise, although opposition to motorways on noise grounds is increasing, whereas many publicity campaigns have been staged concerning airport noise. It would of course be wrong to conclude that road traffic noise is less of a problem than airport noise, since an airport may affect a very large number of people living in a relatively small area; these people receive information from local newspapers and broadcasts and any protest is easily communicated. A given road, however, interferes with a considerably smaller number of people and in any case these tend to be geographically well spread. Furthermore, noise nuisance from aircraft tends to be an all-or-none feature and had an observable beginning when jet aircraft were introduced, whereas road traffic noise is building up steadily with time. Thus, a sociological methodology of studying the interactions within a community would be of little use and hence we can concern ourselves with individuals (this is not to say an individual's behaviour is not modified by the corrrmunity but merely that this modification will be slight). Even at an individual level, complaints are very rare but even this fact is no indication that no-one is disturbed or annoyed, a social class factor may be at work here; it seems reasonable to assume that lower-class people will be obliged to live in a noisier environment and these people are less likely to have the knowledge or the funds to initiate a well-planned complaint. Social class apart, the public has learnt that complaints rarely bring about an improvement, even when a solution is obvious, and in the case of road traffic noise no solution is foreseeable, so the motivation to complain is very weak. Further, even if an individual decides to make a complaint, he is then faced with the decision of to whom his is to complain; the multiplicity of individuals and bodies to whom a complaint could be addressed is very great indeed and as none of them is likely to bring a solution the would-be complainant is likely to reconsider. It is our experience that people become accustomed to unfavourable features in the environment and then merely accept them, although they would like to alter them.

There is no evidence to suggest that illness, either physical or mental, is caused by road traffic noise. 6-8 Thus if we were to judge the nuisance value of road traffic noise by observed community action, complaints or increase in illness, it would appear that the nuisance due to road traffic noise is not great; open-ended inter- viewing, however, shows that it is very real and can occur at a very significant level at which people say they want to move house, 9 and at a more subtle level--


windows have to be closed to watch television, sleep is disturbed, the odd headache occurs, the occasional cup is dropped. Almost everyone in the country is subjected to road traffic noise to some extent and several factors are now combining to worsen the si tuation--there is the ever-increasing horsepower used on the road, the building of urban motorways which bring high traffic speeds and densities and also heavy night traffic into concentrated housing areas; elevated roads can increase the problem and high buildings are particularly susceptible to noise. High land costs and increasing demand for housing enforces that houses are built as near as possible to noisy roads. It is therefore desirable that intensive, subjective studies should be made now and criteria established above which road traffic noise should not be allowed to rise so that noise nuisance can be reduced at the planning level.

THE PSYCHOLOGICAL MEASURE

It is hoped to administer the psychological measuring instrument before physical measurements are made to avoid preconditioning the sample. Our thesis is that there may be two factors which relate to noise- -a disturbance factor which would primarily be a function of the physical parameters of the noise, and an annoyance factor which would mainly depend on personality and the information carried by the noise. These factors can be represented by two vectors in space inclined at an an angle to one another; this angle is a function of their inter-dependence.

There are two ways in which it may be possible to measure nuisance due to noise: an attitude scale and a rating procedure, both of which can be constructed by traditional scaling techniques. 1 o An attitude scale would be composed of questions relating to noise in general, such as 'noise is a cancer of our age' and 'people who make unnecessary noise should be fined'. A rating procedure, however, would be composed of questions relating specifically to the noise present in the person's environment, such as ' the noise round here gives me a headache' or "sometimes it is necessary to close the wirMows'. A person's attitude towards the noise will be only partly a fraction of the noise he suffers and will also contain personality factors, and it could thus prove difficult to estimate disturbance suffered from a score on an attitude scale. I t may be possible to combine the two types of scales in one questionnaire and extract two factors, i.e. a disturbance factor and an annoyance factor by means of factor analysis, t 1

Noise is not the only undesirable attribute of road traffic; fear of accidents, fumes and vibration are others which are often mentioned, and whilst these are not our prime concern they must be borne in mind so as not to compound the survey with significant interactions. An account must be taken of the pleasant attributes of roads, such as convenience and reassurance of the existence of other people. What is required is an unidimensional noise disturbance scale or at least a scale in which the amount of variance due to noise disturbance is known. If this is

ROAD TRAFFIC NOISE--ITS NUISANCE VALUE 283

not so then it would be possible to have two subjects scoring the same on the disturbance scale but for different reasons. I f the noise from a road is reduced the disturbance may remain the same due to other factors; on the other hand it may be possible to leave the noise level unchanged and reduce disturbance by changing other factors.

There is a good deal of evidence to suggest that, due mainly to individual variation in sensitivity to noise, high correlations cannot be obtained between individual disturbance scores and noise parameters. 12- 14 A recent pilot study t 5 has reported a correlation of 0.64 between individual annoyance score and distance from a railway line; it is the authors ' opinion that by using a reliable, well-designed scale high individual correlations can be obtained. I f this cannot be achieved an at tempt will be made to isolate the factors preventing this and these may be sensitivity factors, personality factors or other environmental factors. All psychological measures as well as physical ones must possess reliability and validity. To show that the test is reliable is not unduly difficult, and perhaps the best technique is the test/re-test method although cheaper and more convenient methods may be used. Our biggest problem is one of showing a scale to be valid. It is not sufficient to construct a scale and show that this correlates highly with physical parameters of the noise. All that could be deduced from such a study is that the observer is a consistent estimator of the parameters involved and not that these parameters are disturbing.

The scale must be shown to be a measure of disturbance independently and thus must distinguish between people who are, and who are not, disturbed. Examples of groups which are disturbed and annoyed are complainants and members of the Noise Abatement Society and people who moved house because of road traffic noise. It would indeed be adequate if we could show a negative correlation between high scores and length of time resident in a house. Obtaining validity by this method is ruled out because of the time and inconvenience needed to collect the data. To show that high scorers complained or joined the Noise Abatement Society would be incorrect due to the personality, social and intellectual factors involved; in point of fact, we could by accident validate a measure of these factors. It thus seems that we will not be able to achieve an empirical validity and must content ourselves with a more theoretical validity.

THE PHYSICAL MEASURE

There are numerous physical characteristics of noise, and whilst the recording and analysis of these variables presents no theoretical problems practically, it can be a laborious procedure. At the present time the inter-relationships of the parameter of noise which cause a nuisance are not known.


To investigate all the physical factors of noise would be a considerable undertaking. The only general rule that can be used with any degree of confidence when predicting the nuisance value of a noise is: the louder the noise (i.e. the higher the sound pressure level), the greater will be the nuisance if all other variables are constant. In our initial study we intend to measure sound pressure level only. This is not so unreasonable a methodology as may at first appear, since the spectrum

X•t ~ Statistical.

Lever distribution recorder analyser

Microphone recorder I \ t ,~ Frequency

anatyser I Fig. 1. Block diagram of noise analysis.

120 ! ,oo 8O

so

C =,-

o l n ~ - o 20

v

100 1000 10,000 Frequency,Hz

Fig. 2. Equal loudness level curves.

of road traffic noise can be expected to be typical for a given type of road, as can the variation of traffic densities with time and the stochastic pattern of cars. Our initial study will be on motorways, and if our results do not generalise to other types of road then other factors must be investigated such as the sound spectrum and daily flow pattern. The measurement of sound pressure level is a simple procedure requiring a microphone and tape recorder; the tape can then be replayed through a level recorder and a trace of sound pressure level against time obtained. By connect- ing the level recorder to a statistical noise analyser it is possible to obtain percentage values (Fig. 1). Work by the Building Research Station 12 has shown that a sample of 100 seconds per hour gives a reliable picture of the noise climate. For


every subject in the survey this would take a considerable time, even with a small survey of fifty people; the problems here will be discussed later. Sound pressure level is not synonymous with loudness level, due to the ear's non-linear response to sound of different frequencies and intensities, although the A, B and C weighting

120

u~ t -

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O.

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110

100

90

80

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/ .0 I I I I I I t 30 /.0 50 60 70 80 90 100

A - w e i g h t e d s o u n d leve l in dB

Fig. 3. Plot o f loudness levels versus sound levels.

networks have been devised from equal loudness level curves in an attempt to correct for this (Fig. 2). Equal loudness level curves are used to assess the loudness level of pure tones; complex sounds require detailed calculations using the Zwicker phon method '6 or the Stevens phon method. 17 This problem has been considered '8"~9 and for a large sample of traffic noises correlations in the order of 0-95 have been obtained between dBA and Zwicker and Stevens phons (Fig. 3). It therefore seems fair to consider dBA as a loudness level; slightly more accuracy can be obtained from the regression line of phons on dBA. We intend to (i) take our


recordings on the linear scale in order to lose as little information as possible and then pass them through the 'A ' weighting network and (ii) obtain percentage levels and begin looking for correlations with the dissatisfaction scores. Higher correlations may be found by converting the dBA levels to phons or sones. The sone scale is a ratio scale, whereas the decibel and phon scale are not (Fig. 4). The search for the psychophysical function (i.e. the relationship between physical units and subjective units) was begun by Weber in the last century and is still not established beyond argument. Weber's law states that for a large range of values the ratio of the intensities of two stimuli that can be sensed as being different will be a constant

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Fig. 4. Sones versus phons.

100 110

over a wide range of stimuli intensities and frequencies. This law in itself is not sufficient to construct a psychophysical scale, and another postulate is required. The two widely accepted psychophysical scales are the logarithmic scale due to Fechner and the sone scale originated by Stevens. It has been shown that neither scale is wrong but that each is dependent on the axiom of the psychometric method used to establish the scale, and that in point of fact there could be an infinite number of 'psychometric scales'. 20

The concept of perceived noise levels 21 is an excellent one as this is a direct measure of annoyance, but it has been devised for jet aircraft noise, which has a large high frequency component. It is unlikely that such a concept could be extended to road traffic noise, which is a continuous noise in contrast to the discrete number of noises that enables each aircraft to be given an annoyance value.

ROAD TRAFFIC N O I S E - - I T S NUISANCE VALUE 287

CRITERIA

I f a high correlation can be obtained between disturbance and some physical properties of the noise, the problem will still remain of how much noise a person can be expected to tolerate. At present the two widely held standards with respect to road traffic noise are the Wilson Criteria (Table 1) and the Noise Rating (NR)

T A B L E 1

TENTATIVE ESTIMATE OF THE NOISE LEVELS WHICH MUST NOT BE EXCEEDED FOR MORE

THAN 10~/o OF THE TIME INSIDE LIVING ROOMS AND BEDROOMS

dBA Situation Day Night

C o u n t r y a r e a s 40 30 S u b u r b a n a r e a s a w a y f r o m m a i n

traffic r o u t e s 45 35 B u s y u r b a n a r e a s 50 35

Curves of Kosten and Van Os 22 (Fig. 5); neither are based on extensive social surveys but are recommendations made by leading acousticians on what evidence is available and take some account of prevailing acoustic conditions and economic factors. Although the N R curves give a spectrum, little difference is found between the two recommendations when applied with respect to road traffic noise.

A social survey was conducted into the nuisance caused by aircraft at Heathrow Airport and the Noise and Number Index (NNI) obtained which correlated highly with dissatisfaction. 23 An administrative body was set up to decide the boundaries in terms of N N I values and thus declare which houses should receive grants for providing sound-proofing. Similarly, we can expect that any noise control criteria will be subject to arbitration by an administrative body. The rigid application of a traffic noise criterion will not always lead to an opt imum noise climate for the area concerned. Consider two alternative paths for a motorway through a town, one which would result in several hundred people subjected to noise but at a value slightly less than the criterion, whilst the other would affect only a handful of people but at a slightly higher level than the criterion. The second alternative is more sensible, although some people would be living above the criterion.

Practical cases are never as clear-cut as the above, and any decision-making process is a complex one. It may be possible to simplify this process if our disturbance scale is a ratio scale, i.e. we can speak about people being twice as disturbed as others. The decision would remain to be made but could be phrased in terms such as 'which is it better to do, interfere with half as many people twice as much, or twice as many people half as much? '


This problem arises to a far greater extent when considering aircraft noise problems, when the orientation of a runway or the site of a new airfield has to be decided. The Index of Community Annoyance is being used at Loughborough University 26 when planning airports; the weightings between number o e people annoyed and level of annoyance, however, are very arbitrary.

Noise rating number

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Criterion Broadcasting studio 15 Concert hall, legitimate theatre,

500 seats 20 Class room, music room, TV studio,

conference room, 50 seats 25 Sleeping room (see for corrections

below) 25 Conference room, 20 seats, or with

public address system, cinema, hospital, church, courtroom, library 30

Living room (see for corrections below) 30

Private office 40 Restaurant 45 Gymnasium 50 Office (typewriters) 55 Workshop 65

Corrections for dwellings (a) Pure tone easily perceptible - 5 (b) Impulsive and/or intermittent --5 (c) Noise only during working hours + 5 (d) Noise during 25% of time + 5

6% + 1 0 1-5% +15 0.5 % +20 0-1% +25 0.02 % + 30

(e) Economic tie + 5 (f) Very quiet suburban --5

Suburban 0 Residential urban + 5 Urban near some industry + 10 Area of heavy industry + 15

Noise rating number.

SOCIAL SURVEYS

Very few social surveys have been conducted into the effects of road traffic noise; however, Swedish and French work is at present progressing in this area.

The two major contributions to this field of study are the mean annoyance level

(0 ) 25 and the Traffic Noise Index (TNI). 1 t.26 Only T N I will be discussed, for four reasons:


m

(i) TNI would appear to be a better prediction of dissatisfaction than Q. (ii) Q is more difficult to calculate than TNI since

=/Clog 1/100 z 10Oi//Cf

where K is an empirically determined constant, Qi is the median sound level for the 5-dBA interval i and f~ is the percentage of sound levels falling in the interval.

(iii) Two values of Qare needed, one for day and one for night. (iv) Much of the work and references relating to Q are not yet translated from

the German.

The TNI survey was conducted by the Building Research Station; fourteen sites in North-West London were selected, some being alongside dual carriageways and some alongside single carriageways. The noise climate was assumed to be the same throughout the site and only one noise measurement was made at each site, and this consisted of a 100-second sample taken every hour for 24 hours. Approxi- mately 100 people were interviewed at each site and the psychological measuring instrument consisted of a 7-point rating scale with only the end points named:

Definitely satisfactory (1) (2) (3) (4) (5) (6) (7) Definitely unsatisfactory

102 96 9~ 9O

T.N.I. 86 82 78 7& 7O 66 62 58

Fig. 6.

J

/ / f / f / /

o Y / ~ / / / / opilot survey sites

/ j x / " xrnain survey sites / / / Corretation (~sites onty)

-~ - r = * 0 . 8 8 / / p<0.001

I I I I I t i

"1'0 2.0 3"0 4-0 5.0 6"0 Dissat isfact ion score

l , I I I )

; lo 2s so do 7s 9'o Percentil.es

R¢srcssion of dissatisfaction on traffic noise index (TNI) with confidence limits at 4-2 standard errors of estimate shown.

In addition there were numerous other questions. The noise was analysed statisti- cally into 10%, 50% and 90% levels. The 10% level shows the peaks in the sound whereas the 90 % level can be considered as background noise levels. Correlations


between individual dissatisfaction scored and these levels were not high but very significant due to the large number involved. By correlating the median dissatisfaction score for each site with these levels, considerably higher correlations were obtained. A technique known as multiple correlation was then used and a function of the 10~ and 9 0 ~ levels obtained which correlated to a degree of 0.81 with median dissatisfaction scores for the sites (Fig. 6). A correlation of 0.88 could be obtained by removing subjects who scored 4 on the dissatisfaction scale.

90

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40

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10 20 40 80 met res

Fig. 7. Attenuat ion o f noise with distance.

I

160

The resulting function was named the Tratfic Noise Index and is expressed as:

TNI = 4(10~o level - 90~o level) + 9 0 ~ level - 30

where 30 is an arbitrary constant. The seven point scale was shown to be reliable by a modified split-half pro-

cedure. The scale was shown to be valid by means of other questions on the questionnaire such as 'are you ever woken by a noise from this road?' and 'are you ever woken by the noise stopping?' People scoring high on the dissatisfaction score tended to answer 'yes' to these questions.

Thus from a regression line of dissatisfaction on TNI it is possible to predict fairly accurately dissatisfaction from the TNI.


Acr i ter ion is still required which specifies the highest acceptable level. The l 0 % level was found to decay at a rate of 6 dB per doubling of distance and

the 90 % level at a rate of 3 dB per doubling distance (Fig. 7). This enables the effect of distance on T N I to be easily computed. It can be seen (Fig. 8) that at 100 metres even the highest possible roadside values of T N I have been reduced to a value of 74. I f 74 TNI is an acceptable criterion, there is a great variance with the Wilson recommendations and Noise Rating curves. These latter methods show that 600 metres can be required before acceptable limits are reached.

The T N I is an excellent study and the most comprehensive we have to date. The validity of the dissatisfaction scale is a construct validity and not an empirical

7O

2 50 ~- 10 20 30/.0 60 80 100 200

Distance, metres Fig. 8. Minimum acceptable distance from road.

validity which would be preferable, but as we have suggested earlier, an empirical validity is probably impossible to achieve. The T N I was based on a limited sample of both types of people and roads, and it would not be fair to apply it to other types of roads or people without further work. Figure 9 shows the variation in T N I against a change in 90% level for a constant 10% level. I t can be seen that when the 90 % level tends to the 10 % level the T N I becomes low. Indeed, a constant 100 dBA noise gives a T N I of 70. Although not suggesting that traffic noise becomes constant it is possible tlaat a pattern is intrinsic in the flow of motorway traffic, and this may prevent generalisation to other types of road.

The initial report on the T N I did not propose any criteria; the criterion of 74 TNI was tentatively proposed in a later report 26 and the authors stress that no scientific method could be used to deduce a criterion. The reasons for proposing 74 TNI are:

(l) The median dissatisfaction score of all people interviewed was 4.4; 74 is the value of TNI equivalent within statistical error to 4.4 on the dissatisfaction scale. It is thus suggested that the median dissatisfaction score of the sample interviewed is a reasonable criterion to accept. This can be challenged for two reasons:

(a) the sample tested is not representative of the population; people living in the country may not be as tolerant of noise as town dwellers, and,

292 C. G . BOTTOM~ D. J. C R O O M E

(b) even if the sample was representative, what is in fact being proposed is that the 'average noise' should be used as a criterion for planning and no decision is being made as to whether people should be subjected to more or less noise. (2) The accuracy of the regression is greatest about the mean; basing of a criterion

on a statistical artifact would not seem valid.

TNI

l t .0

120

100

80

60

/.0

\

\ \

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I I I I I I l I 0 40 50 60 70 80 90 100

90'/, [eve[ dBA

F i g . 9. T N I v e r s u s 9 0 ~ l eve l .

(3) The worst existing noise climate encountered could be reduced to a level equivalent to 74 TNI by simple acoustic double glazing. The TNI did not attempt to separate the internal environment from the external environment. Thus disturbance may still occur when residents are spending time in the garden; this could be quite important during the summer.

P L A N OF R E S E A R C H

Our plan of research can essentially be divided into two factors:

(i) subjective assessment of annoyance and disturbance caused by road traffic noise;

(ii) physical studies of noise levels in high buildings and also in a row of houses shielded by other rows of houses.

We intend to try and find high correlations between individual scores on a dissatisfaction annoyance scale and combinations of loudness levels (though not necessarily the TNI). During the first pilot study about 100 people will be interviewed; all will be given the 7-point scale used in the TNI. About 50 people will be given a large questionnaire containing questions relating to all aspects of the


unpleasant and pleasant aspects of living near a road, including noise, fumes, vibration, fear of accidents, loss of value to property and general loss of amenity; these responses will be analysed by means of a factor analysis and the number of factors isolated. Scores on the questions relating to noise will then be correlated with noise measures. A questionnaire constructed by the Thurstone method will be administered to the remainder in an attempt to measure disturbance. This will be constructed by taking a large number of statements about noise in the home and having these sorted into eleven ranked piles by judges; statements which considered noise unintrusive, such as 'the noise here doesn't bother me' would be placed in low piles, whilst statements which considered noise intrusive, such as 'at times I can hardly hear the television because of the noise' would be placed in high piles. About ten statements which showed the highest inter-judge agreement would then be used to construct the questionnaire. Each statement used would be given a value of the mean of the judges' value. Theoretically the respondant should only agree with one, in which case the respondant's disturbance score is equal to the value given to the statement. In practice it is often more than this and the mean value of all statements agreed to is taken. The people given the Thurstone type scale will also be given a scale in the form:

Do you ever hear the noise here? Do you ever complain to yourself about the noise here? Do you ever complain to a member of your household? Do you ever complain to a friend or neighbour? Have you ever made an official complaint, e.g. newspaper? Have you made more than one official complaint?

which is an attempt to measure annoyance. The five questions of McKennell 's airport study used to derive the NNI will

also be given. In addition other factors such as age, sex, social class, will be noted. Scores on all the above scales will then be correlated with levels of the noise.

Any scale stating high correlations will be re-administered to show that it is reliable. I f high correlations cannot be obtained, personality tests will be administered. I f high correlations can be obtained studies will be conducted on different kinds of road to see if the parameters of the noise isolated can also be used to predict disturbance on other types of road. If high individual correlations cannot be obtained we will proceed using the 7-point scale only, and virtually repeat the TNI study, firstly for motorways, then for different types of road.

The noise will be sampled 100 seconds every hour for 24 hours, and this raises a problem since the traffic using the motorway differs from day to day; we intend to assume, however, that weekdays will have a similar traffic flow. Noise will be recorded outside the home as people may object to having a microphone inside their houses, and also internal noise sources may contaminate the recordings. All the houses in the pilot study will be of similar construction and therefore have

294 C. G. BOTTOM, D . J . CROOME

similar acoustic properties. To record the noise outside every house would be a considerable undertaking and also unnecessary. What we require ideally is several rows of houses parallel to the motorway at varying distances from it (Fig. 10), with little traffic on the minor roads between the houses.

c R - - R I-T-l-q Fr-r-q FTT-] 3 3 3 ' ~ ~ R o w s

b F-FR Fr-m F-I-I-I F - r - -F ] - - o, 2 2 2 .houses

, FFR F1-R F-F-F] F-FT] r - F m J 1 1 1

Motorway

Fig. I0. Ideal site.

The shielding effect of one row on another can also be studied. Microphones can be placed in position (1), then (2), then (3), etc., and noise recorded continu- ously for a considerable time. I f all the recordings on a given row are reasonably alike we can assume all the people on that row have the same noise climate, and then the 24-hour sample can be taken with microphones in position (a), (b) and (c). Whether an ideal case can be found in practice is doubtful, and considerably more measurements may be necessary than we anticipate.

By this method we also hope to collect data to verify or refute the theory that noise from an unseen source is less annoying and disturbing than noise from a visible source. The definition of visible in this context is difficult, but some arbitrary qualification such as ' f rom how many rooms in the house is the motorway visible' should be possible. This will be measured subjectively and objectively since the important factor may not be how much of the noise source the subject sees, but how much he thinks he sees. It is also hoped to collect data from houses shielded from the motorway by trees or other natural features to see if this reduces annoyance or disturbance more than a screen of houses.

The study on a tall building will be primarily objective though some question- naires may be administered, readings being taken at differing heights on the building, then on the different faces of a building at a constant height.

GLOSSARY OF STATISTICAL TERMS

Construct Validity. Validity given by the existence of an hypothetical construct. Correlation. A measure of the tendency of two series of measurements to vary

concomitantly.


Empirical Validity. Validity given by means of a correlat ion between test scores and some independent index.

Factor Analysis. Statistical analysis of the correlat ions between scale scores to extract the n u m b e r of relevant variables.

Median. The middle value in a series of values arranged in order of magni tude. Mult iple Correlation. The combina t ion of two or more variables to give the

highest correlat ion with one another . Ratio Scale. A scale with an absolute zero and with equal intervals between

numbers , e.g. length. Regression. A method of ob ta in ing the best fit of a line to data by a technique

of least squares. Two such lines are possible depending on which variable is to be

predicted. Reliability. The repeatabil i ty of a measure. SpBt Half . A psychological scale is considered as two shorter scales which are

measur ing the same attr ibute. Correla t ion of these halves gives a measure of reliability.

Test~Re-test. A psychological scale is re-administered and the correlat ion between the two sets of scores is taken as an index of reliability.

REFERENCES

1. R. LAWRENCE, The influence of traffic noise on the design of external walls of buildings, 6th Intern. Congr. on Acoustics, Tokyo, 1968.

2. ZYUN-Iarq MEAKAWA, Reduction of noise by barriers, Memoirs of the Faculty of Engineering, Kobe University, No. 11, 1965.

3. E. J. RiCrtARDS and D. J. CROOME, The problem of traffic noise, Roads in the Landscape Symposium, Ministry of Transport, 1967.

4. T. PmEDE, Noise and vibration problems in commerce vehicles, J. Sound Vib., 5 0967) 129. 5. D. E. BROADIDENT, Perception and Communication, Pergamon, Oxford, 1958. 6. W. BURNS, Noise and Man, John Murray, London, 1968. 7. B. DAVIS (Ed.), Auditory and non-auditory effects of high intensity noise, Project ANEHIN:

Final Report, doint Project 13 01, "Subtask 1, Report No. 7, Central Institute for the Deaf, St Louis, Mo., and US Naval School of Aviation Medicine, Pensacola, Fla, 1958.

8. Committee on the problem of noise, final report, Cmnd 2056, HMSO, London, 1963. 9. M. BACELON and C. LAMURE, CIB Bulletin N 1-2, 1966.

10. J. P. GUILFORD, Psychometric Method, McGraw-Hill, New York, 1954. 11. H. BARMAN, Modern Factor Analysis, University of Chicago Press, 1965. 12. I. D. GRIFFI'naS and F. J. LANGIX)N, Subjective response to road traffic noise, BIdg Res. Sta.,

C.P. 37/68, 1968. 13. F. J. LANGDON, Research on noise nuisance, CIB Symposium, 1966. 14. A. C. MCKENNEL and E. A. HUNT, Noise Annoyance in Central London, The Government

Social Survey, 8.S.332, 1966. 15. D. WALTERS, Railway noise in housing areas, unpublished pilot study, Birmingham School of

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Levels, Bldg. Res. Sta. Note No. B.237 (restricted), 1961. 19. J. H. BOTSFORD, The Weighting Game, Acoustical Society of America, May 1968. 20. m. TRIESMAN, Sensory scaling and the psychophysical law, Quart. J. Exptl Psychol. 16 (1964).


21. K. D. KRYTER, Scaling human reactions to the sound from aircraft, J. Acoust. Soc. Am., 31 (1959) 1415.

22. C. W. KOSTEN and G. J. VAN OS, The control of noise, NPL Symposium No. 12, HMSO, London, 1962.

23. A. C. MCKENNELL, Aircraft noise annoyance round London Heathrow Airport, London UK Central Office of Information, 1963.

24. C. S. WATEgS, Airport Noise and the Community, Soc. Environ. Engrs, London, 1969. 25. J. LANG, Verkehrsffu'm--Messung und Darstellung, F.35, 5e Congr~s International

d'Acoustique, Liege, Sept. 1965. 26. F. J. LANGDON and W. E. S¢,OLES, The traffic noise index--a method of controlling noise

nuisance, Bldg. Res. Sta., C.P. 38/68, 1968.

road traffic noise—its nuisance value

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