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TRANSPORT and ROAD RESEARCH LABORATORY

Department of the Environment Department of Transport

TRRL LABORATORY REPORT 1015

ENVIRONMENTAL EFFECTS OF TRAFFIC CHANGES

by

A M Mackie and C H Davies

Any views expressed in this Report are not necessarily those of the Department of the Environment or of the Department of Transport

Access and Mobility Division Transport Operations Department

Transport and Road Research Laboratory Crowthorne, Berkshire

1981 ISSN 0305-1293

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on I st April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

Abstract

1.

2.

3.

4.

.

C O N T E N T S

Introduction

Method of study

The sites

Physical measures

4.1 Traffic flow

4.2 Noise

4.3 Air pollution

4.4 Vibration

Traffic nuisance

5.1 General disturbance

5.2 Causes of traffic nuisance

5.2.1 People at home

5.2.2 Pedestrians

5.2.3 Shop workers

5.2.4 Office workers

5.3 Effect of noise on nuisance

5.4 Effect of dust and dirt

5.5

5.6

5.7

Opinions on the effect of vibration

Effect of smoke and fumes

Relation between general traffic nuisance and nuisance from particular factors

6. Behavioural effects

6.1 Effects on particular activities

6.2 Severance

7. Short term as opposed to long term effects

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8. Respondents' expectations

9. Relation between traffic and nuisance to people at home

9.1 Correlations - actual levels for people at home

9.2 Relation between changes in nuisance and changes in flow

10. Conclusions '

11. Acknowledgements

12. References

13. Appendix: Alternative equations for predicting the level of nuisance

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© CROWN COPYRIGHT 1981 Extracts from the text may be reproduced, except for

commercial purposes, provided the source is acknowledged

ENVIRONMENTAL EFFECTS OF TRAFFIC CHANGES

ABSTRACT

The report describes a study of the environmental effects of traffic and traffic changes in nine towns where changes in traffic flow had occurred due to by-pass construction or traffic management schemes. An assessment of the nuisance caused by particular traffic flows has been made. The study also examined the effects of noise and air pollution on people's sensitivity to traffic. Nuisance was measured by means of personal interview surveys of people at home, pedestrians and people working in shops and offices. Nuisance levels changed considerably when the traffic levels changed.

The single traffic variable most strongly correlated with nuisance was the number of lorries over 16 tons GVW, but there was also a high correlation between nuisance and total traffic flow. A multiple regression analysis showed that these two variables could explain 85 per cent of the variance in the nuisance data.

1. INTRODUCTION

There has been considerable interest, in recent years, in assessing the environmental effects of traffic. The

purpose has been either to estimate the impact of new roads and traffic management schemes or to identify

those locations in most need of relief from undesirable traffic effects. It was thought important to know

the actual levels of nuisance which particular traffic flows caused, the factors which caused nuisance and

also the changes in people's opinions of nuisance when a change in the amount of traffic occurred. This

interest was reflected in the attention the 'Advisory Committee on Trunk Road Assessment '1 paid to the

assessment of environmental factors as an essential element in the appraisal o f trunk road schemes. New

roads may increasingly be built for environmental rather than traffic benefits so it has become more

important to assess the environmental impact 2.

A series of 'before' and 'after' studies have therefore been carried out using a common methodology

at ten sites in nine towns where changes in traffic flow occurred as a result of new road construction or

traffic management schemes. These studies enabled an assessment of levels of nuisance for particular traffic

flows to be made, and also made possible an examination of the effect of various other characteristics on

people's sensitivity to traffic nuisance. This report brings these studies 3"7 together and attempts to derive

general conclusions. It is the only study available which investigates the effects of changes in traffic on

the public's attitude to nuisance. Other related studies have concentrated on the effect of road construction

on economic activity or land use in towns 8,9.

2. METHOD OF STUDY

In the study three types of measurement were made - measures of (1) subjective attitudes to traffic

nuisance, (2) effects of traffic on behaviour and (3) physical changes.

Measurements were made both before and after the changes in flow occurred. The after measurements,

in most cases, followed three to six months after the change in traffic flow had occurred. Both the attitudinal

and behavioural effects were measured by means of personal interview surveys amongst pedestrians, people

at home and workers in shops and offices in the roads affected by the traffic changes. Many detailed effects

were asked about, and a composite picture of attitudes to traffic nuisance was built up in terms of the

incidence of nuisance, the strength of feeling about the problem, the particular effects and the activities disturbed.

To find what influenced attitudes to traffic nuisance, these interview data were supplemented by

physical measurements of traffic flow, composition of flow, noise, vibration and air pollution.

At one of the sites (Tdng) a second 'after' study was carded out, one year and three months after the

first, in order to investigate the process of adaptation to the new traffic conditions, and to fred out whether

people's opinions of improvement in conditions were eroded through time:

3. THE SITES

In all the Laboratory has studied 13 sites in this research programme. The first, Alton, was used to develop

the questionnaire and measurement techniques 3. Two others, Keswick and Cockermouth 10 formed part

of fi larger study of the regional impact of improvements to a major trunk road route, the A66. Consequently

the experimental methodology in these three surveys does not match that used in the other ten. The ten,

with a common methodology, are listed in Table 1 and provide the data for this comparative analysis.

TABLE 1

The sites studied

Town Road number Type of change Population

Tring

Mere

Boughton

Bridge

Lewes

Stafford

East Grinstead

Ludlow

Leeds

Leeds

A41

A303

A2

A2

A27

By-pass of town

By-pass of town

By-pass of town

By-pass of town

By-pass of town

9590

2085

1500

1000

14,159

A34

A22

A49

A58

A64

Inner relief road

Inner relief road

By-pass of town

Lorries prohibited

One of the roads where lorry numbers increased

55,000

16,560

6780

I

I NE edge of city I

!

2

These sites include a range of size of community, from the very small, little more than villages,

eg Boughton and Bridge in Kent, to medium sized towns, such as Stafford. Effects in large urban areas

have not been studied except for a lorry control scheme in and on the edge Of the city of Leeds. The majority of the sites experienced a reduction in traffic due to by-pass construction. In both Stafford and

East Grinstead the new road was an inner relief road rather than a town by-pass. The two sites in Leeds

experienced changes in traffic due to a lorry control scheme, in which one of the roads had a decrease in

lorry flows and the other an increase. The purpose of the scheme was to divert lorry traffic from the A58

on to more suitable routes. The A64 was one of the routes on to which lorries diverted, and is therefore

the only site of the ten where the change in traffic was an increase rather than a decrease in flow.

All the sites were chosen so that there was a range in total traffic flow and also in the size of the

changes in flow.

4. PHYSICAL MEASURES

4.1 Traffic flow

All the town roads surveyed were 'A' class Primary routes, and therefore carried substantial traffic

flows. The levels for weekday 16 hour flows, ie from 0600 hours to 2200 hours, are shown in Table 2. The percentage of medium (3 to 16 tons gross vehicle weight) and heavy (over 16 tons gross vehicle weight)

goods vehicles are also given.

TABLE 2

Changes in town centre traffic flow

Site

16 hr flow

Before

%

medium 1

Tring - A41 15,400 10

Mere - A303 10,585 7

Boughton - A2 11,470 11

Bridge - A2 9,510 11

Lewes - A27 13,410 11

Stafford - A34 11,615 13

East Grinstead - A22 15,730 11

Ludlow - A49 12,010 8

Leeds - A58 15,060 13

Leeds - A64 14,050 11

Medium = vehicles 3 -16 t GVW Heavies -- vehicles more than 16t GVW

%

heavy 2

5

4%

9

8

3

2

4

6

8

6

16 hr flow

After

%

medium 1

% heavy 2

Percentage change

16 hr flow

9,050 6 2 -41

3,255 6 2 - 6 9

2,160 11 2 "81

1,390 12 1 - 8 5

7,300 11 2 - 4 6

5,280 20 1 - 5 5

9,280 8 3 -41

5,400 7 3 - 5 5

14,550 9 1 - 3

16,260 13 11 +16

3

In all the by-passed towns there was a substantial decrease in flow ranging from an 85 per cent

reduction in Bridge to a 41 per cent reduction in Tring and East Grinstead. The changes in flow due to

by-passes or relief roads were related to the size of town in that the smaller the town the higher the

proportion of through traffic compared with locally generated traffic. This relation is shown in Figure 1

and compared with a similar relation developed previously in a desk study 11. The measured data agree

well with the desk study data. Figure 1 shows that unless other traffic management measures are also

taken, it is only in the small towns, less than 10 000 population, that more than half the traffic is removed

by by-pass or relief road construction. This has implications for the public's expectations of benefits from

by-passes which is dealt with in a later section. Table 2 shows the composition of traffic flow. Three

categories have been used - (1) cars and light vans less than 3 tons gross vehicle weight; (2) medium goods

vehicles 3 to 16 tons gross vehicle weight and (3) heavy goods vehicles over 16 tons gross vehicle weight.

It was unusual for categories 2 and 3 together to form more than 20 per cent of the flow and category 3,

the heavy goods vehicles were generally under 10 per cent. The effect of all the schemes was to achieve a

proportionately larger change in the flow of the heavy goods vehicles compared with other types of vehicle,

often reducing them to only 1 or 2 per cent of the total traffic flow.

The highest percentages of heavy lorries were on the A2 at Bridge and Boughton, the A58 and A64

in Leeds and the A49 in Ludlow where percentages of up to 11 were recorded.

4.2 Noise

Noise was measured at all sites out o f doors at a receiver height of 1.5m above ground and at a distance

of l m from the building facade. The 18 hour L10 dB(A) index was used to express the level of noise. This

index is the arithmetric mean of the 18 hourly noise levels, in dB(A), exceeded for 10 per cent of the time

for the period 0600-2400 hours on a normal working day. It is the traffic noise index most generally used in the United Kingdom 12,13.

The results for the ten sites are given in Table 3. The levels given refer to one address at each site.

For the by-passed towns this was close to the town centre.

TABLE 3

Change in noise levels - 18 hour L10 dB(A)

Predicted from Sites Before After Change measured traffic change

Tring

Mere

Boughton

Bridge

Lewes

Stafford

East Grinstead

Ludlow

Leeds - A38

Leeds - A64

75.6

76.9

81.6

74.9

79.4

78.5

76.0

75.0

72.5

73.0

70.8

69.0

69.0

59.7

76.5

75.5

70.3

69.9

70.3

74.4

-4 .8

-7 .9

-12.6

-15.2

-2 .9

-3 .0

-5 .7

-5.1

-2 .2

+1.4

-3 .7

-5 .9

-8 .4

-9 .4

-2 .8

-2 .5

-3 .0

-4 .3

-2.1

+1.6

4

Reductions were measured at all the by-pass sites, ranging from about 3 dB(A) at Lewes and Stafford,

to an extremely large change of 15 dB(A) at Bridge. The lorry routeing scheme in Leeds created changes

in the two roads studied but smaller than at the by-pass sites.

To examine the relation between the noise changes and traffic changes the change in noise directly

attributable to the traffic has been calculated using the Department of Transport noise prediction method 14..

The predicted changes are listed in Table 3 and compared with the measured changes in Figure 2. The data

show that the prediction method introduces a systematic error into the assessment of change so that

reductions of noise were invariably underestimated and, in the one case considered, an increase was over-

estimated, though not by a significant amount. In the case of noise reductions the systematic bias was

greater for greater changes ~'.

4.3 Air pollution

At one site (Tring) the Laboratory's mobile air pollution monitoring unit 15 was used to provide data

on the pollutant levels. The site for the measurements was in the main street near the town centre, where

the road width is a minimum for two lanes of traffic. Table 2 has shown that traffic in Tring dropped

from 15,400 vehicles per 16 hour day to 9,050 vehicles. Samples of the air from above the roadside foot-

path were analysed for concentrations of the four pollutants usually associated with motor vehicles (carbon

monoxide, nitric oxide, hydrocarbons and lead) and of sulphur which arises from other sources of combustion. The concentrations o f each of these pollutants is summarised in Table 4.

TABLE 4

Average weekday concentrations of pollutants at Tring

Pollutant

Sulphur (pphm)

Hydrocarbons (ppm)

Carbon Monoxide (ppm)

Nitric Oxide (pphm)

Lead ~g /m 3)

Concentration

Before After

1.0 2.1

3.8 2.8

1.9 2.4

6.9 6.9

1.6 1.4

The levels in both periods were low compared with general levels as indicated by other studies 16,

and it was not possible to demonstrate any significant decrease in the levels as a result of the 41 per cent

decrease in traffic, except possibly in the case of hydrocarbons.

4.4 Vibration

While this programme of surveys was in progress the Laboratory also became involved in developing

techniques to measure vibration and provide information on the levels of traffic induced vibrations in

* Traffic speeds were not measured and so a constant speed, 50 kin/h, has been assumed in the prediction. t Different assumptions about traffic speed could reduce the bias effect but cannot account completely for

the difference between predicted and measured data at Boughton and Bridge,

buildings. Traffic induced vibrations can be generated in buildings either by ground borne vibrations or

air-borne low frequency sound. Ground borne vibrations originate with the variation in contact forces

between the wheels of a vehicle and the road surface. However, when a road conforms to the specifications

for Road and Bridge Works 17, moving vehicles do not normally generate ground vibrations large enough to

be perceived in nearby buildings. Air-borne low frequency sound, however, can induce building vibration

and it is possible that occupants of buildings exposed to high levels of low frequency sound may detect this

vibration either by direct sensations in the body or by heating items such as windows rattling.

It was not possible to carry out before and after measurements at all the sites, but measurements of

vibration due to low frequency sound were made in the before period at Ludlow, Lewes and Stafford, in

buildings 3 to 4m from the kerb. The technique of measurement is dealt with in another report 18, as is a

more detailed analysis of the results 19. Floor vibrations were found in the test houses and primarily were

caused by acoustic excitation at frequencies below 100 Hz. However, only at Ludlow did they exceed

the perception threshold given in a draft ISO standard 20 and there only for 1 per cent of the time.

5. TRAFFIC NUISANCE

5.1 General disturbance

The respondents were asked "Does the traffic here bother you in any way?". The proportions of

each of the groups in the surveys who answered 'Yes' to this question are shown in Table 5.

TABLE 5

Percentage of people bothered by traffic

Before After Sites

People at home

Pedestrians Shop/Office

workers People at

home Pedestrians

Shop/Office workers

Tring 58 81 81 35 43 45

Mere 53 * * 15 * *

Boughton + + + 15 * *

Bridge 80 * * 12 * *

Lewes 52 84 72 49 37 49

Stafford * 56 38 * 30 32

East Grinstead 58 61 64 31 19 40

Ludlow 67 77 71 32 36 26

Leeds - A58 88 * * 59 * *

Leeds - A64 47 * * 90 * *

+ No before study * Not surveyed due to small population available

6

Changes between the before and after periods are generally large and at all sites statistically significant

changes in the incidence of nuisance have occurred. The relation of the amount of improvement to the change

in flow will be dealt with in Section 9.

Table 5 simply gives the percentage of people bothered by traffic - it has been described as the incidence

of traffic nuisance. What is also important, however, is the degree of nuisance - the strength of feeling

against traffic. This was assessed in the study by means of attitude rating scales. One of the scales used

was a 7 point line scale with numerical tags as shown below:

Not at all bothered I I I i i I | Extremely bothered 0 1 2 3 4 5 6

The results are given in Table 6 where it can be seen that although fairly high percentages of people

considered they were bothered by traffic, the degree of nuisance as measured by these scales was at a high

level only at Bridge and in Leeds along the A58 in the before studies, and at the Leeds A64 site in the after

studies. In addition, high levels are likely to have occurred at Boughton and Ludlow. Boughton had a

similar traffic flow to Bridge but no before survey was possible, and at Ludlow a different assessment

method was used.

TABLE 6

Degree of nuisance to people at home from traffic - per cent at each scale position

Scale Median Sites Time 0 ] 1 1 2 3 I 4 1 5 1 6

Before 47 3 2 14 13 8 13 1.7 Mere

After 86 7 4 1 2 0 I 0.3

Before * Boughton After 84 3 4 4 1 0 4 0.3

D~ridge Befo re 21 0 7 15 17 15 25 4.0 After 88 0 5 2 3 2 0 0.3

Before 48 0 2 9 17 6 18 2.5 Lewes

After 50 0 4 25 13 4 4 1.0

Before 43 0 6 10 16 2 23 2.6 East Grinstead

After 69 0 8 6 6 2 8 0.2

Before 33 * Ludlow

After 68 2 10 8 4 3 5 0.2

Before 12 2 4 11 8 9 53 5.5 Leeds - A58

After 41 14 15 15 10 5 2 1.1

Before 53 0 18 14 7 1 7 0.5 Leeds - A64

After 10 3 14 10 13 13 37 4.5

* Limited 'before' data available

7

This scale is probably a slightly better indicator of nuisance than the question indicating how many

people claim to be bothered by traffic, but the two measures of nuisance are in fact well correlated (r = 0.9).

They indicate that at all the by-passed sites nuisance levels are now low; but only at Bridge and probably

Boughton and Ludlow of the by-pass sites plus the Leeds A58 site were conditions considered severe in

the before studies.

This tendency not to rate extremely highly the levels of nuisance may of course be partly due to a

certain amount of self selection or rationalisation taking place; people who live at those sites must f'md it

tolerable otherwise some of them would have moved or not gone there in the first place. Some evidence

in support of the rationalisation hypothesis was found in an experiment where groups of people from four

different streets rated their own street and the three other streets 21. The most heavily trafficked street

was rated less bad by its residents than by the subjects from the other streets (and the street with least

traffic was rated less satisfactory by its residents than by people from the other streets). The fact that in

the before studies significantly more pedestrians, most of whom did not live in the street, were bothered

by traffic than were the people at home may support this hypothesis. In the 'after' studies there were no

statistically significant differences between the two groups.

Although the study has shown statistically significant differences between groups either between sites,

within sites and before and after, it is perhaps surprising to note the great range of individuals' opinions.

At all sites virtually the whole range of the scale was used by respondents, indicating that while some

individuals considered there was no nuisance from traffic, others, in the same circumstances, considered conditions to be extremely unsatisfactory.

5.2 Causes of traffic nuisance

Respondents were asked what it was about traffic that bothered them. Five main nuisance factors

have been identified in the study. These are - (1) danger and difficulty, particularly for pedestrians;

(2) noise; (3) vibration; (4) dust and dirt and (5) smoke and fumes. They all contributed substantially to

nuisance but when their significance relative to each other was rated, it varied somewhat between different

groups, between sites and between 'before' and 'after' occasions (Table 7).

5.2.1 Peop le a t h o m e . Averaged over all sites noise was considered to be the biggest cause of

nuisance, particularly in the 'before' studies when the incidence of nuisance was substantial. However, the

average ranks of importance for danger, vibration and dust and dirt were rarely statistically significantly

lower than for noise. Smoke and fumes appeared to be of less concern and this nuisance was ranked

significantly below the others.

5 .2 .2 Pedes t r ians . Pedestrians at all sites considered that danger and difficulty in crossing the road

was the main factor about traffic that bothered them. Noise and smoke and fumes were ranked about

equal in second place with dust and dirt least important.

5.2.3 Shop workers, Shop workers were interviewed in the premises where they worked. They felt

dust and dirt and noise to be the main nuisance factors, followed by danger; less worrying was vibration

and least important, as with people at home, were smoke and fumes.

5 .2 .4 Office workers. Office workers gave similar responses to people at home in that noise was

considered to be the worst nuisance factor with danger, vibration and dust and dirt equally ranked in

second place. Smoke and fumes again were considered least important. 8

TABLE 7

Nuisance factors average ranks of importance

Respondent group Nuisance factor Before After Overall

People at home

Pedestrians

Shop workers

Office workers

Danger Noise Vibration Dust and dirt Smoke and fumes

Danger Noise Dust and dirt Smoke and fumes



2.8 1.6 2.4 3.1 4.8

1.4 2.2 4.2 2.4

2.6 1.6 3.6 2.0 4.8

3.0 1.0 2.8 2.8 4.4

2.0 2.3 2.8 2.6 4.5

1.6 2.4 3.2 2.0

3.2 2.4 3.0 1.2 4.8

2.6 1.6 2.8 2.8 4.2

2.4 2.0 2.6 2.9 4.6

1.5 2.3 3.7 2.2

2.9 2.0 3.3 1.6 4.8

2.8 1.3 2.8 2.8 4.3

5.3 Effect of noise on nuisance

As described in Section 4.2 above, noise levels were measured at all sites. There was a high

correlation (r = 0.81) between nuisance from noise and general traffic nuisance but the correlation between

actual noise levels and nuisance from noise was not particularly high (r = 0.66). Indeed in the before studies

only, there was very little correlation between noise levels and opinions of bother from noise. This may

have been due to the fact that in the before studies all the noise levels were fairly high and therefore

covered only a narrow range.

Changes in noise levels were, however, well correlated with changes in nuisance from noise (r = 0.81)

and even better with changes in general traffic nuisance (r = 0.94). This is illustrated in Figures 3 and 4

for people interviewed at home in the by-passed towns.

Nuisance from noise was measured by means of a four point verbal scale - bothers 'very much',

'quite a lot', 'not very much' and 'not at all', to which the scores 3 to 0 respectively were assigned. The

median values from this scale have been used in the correlations in Figure 3.

Another way of summarising the results of this scale is to quote the percentages in the top two

categories as shown in Table 8. The change in the amount of nuisance from noise can be seen clearly. It

is interesting to note that in the Leeds lorry routeing scheme, changes in 18 hr L 10 were small but attitudes

to noise nuisance showed large changes.

9

TABLE 8

Change in noise nuisance to people at home

Sites

Per cent bothered 'very much' or 'quite a lot'

by noise Change in noise level L10 dB(A)

After-Before

Before After

Tring 32. 17 -4 .8

Mere 43 7 -7 .9

Boughton - 7 -12 .6

Bridge 49 3 - 15.2

Lewes 55 33 -2 .9

East Grinstead 52 16 -5 .7

Ludlow 55 15 -5.1

Leeds - A58 66 15 -2 .2

Leeds - A64 10 67 +1.4

- no before study done

5,4 Effect of dust and dirt

Dust and dirt proved to be a considerable source of nuisance in the before studies, particularly amongst

shop workers but also for people at home. Changes after the traffic changes were somewhat varied and it was

only where there was a really large change in flow, or at the lorry routeing sites, that opinions of nuisance

changed appreciably. The change in the response of people at home is shown in Table 9.

5.5 Opinions on the effect of vibration

As described in Section 4.4 above, vibrations were found in houses in Lewes, Ludlow and Stafford

in which measurements were made, primarily caused by acoustic excitation at frequencies below 100 Hz.

The magnitude of the vibrations were compared with the perception thresholds given in the draft ISO

standard 17. It was found that vibrations exceeded this perception threshold only at Ludlow and there

for only one per cent of the time. Despite this low level of measured vibration, vibration was considered to

be a major cause of nuisance at many of the sites (see Table 7). Compared with noise, for example,

although fewer people claimed to experience vibration from traffic those who ~ d tended to be more

bothered by it and overall vibration was ranked similarly to noise. The changes in the percentage of people

who were seriously bothered by vibration, after the traffic changes, are shown in Table 10.

10

TABLE 9

Percentage o f people at home bothered 'very much ' or 'quite a lo t ' by dust and dirt

Sites

Per cent bothered 'very much' or 'quite a lo t '

by dust and dirt Traffic change

%

Before After

Tring 40 29 - 4 1

Mere 62 10 - 6 9

Boughton - 11 - 8 1

Bridge 70 0 - 8 5

Lewes 60 57 - 4 6

East Grinstead 44 43 - 4 1

Ludlow 58 49 - 5 5

L e e d s - A58 55 16 - 3

Leeds - A64 33 63 +16

- no before s tudy done

TABLE 10

People at home bothered 'very much ' or 'quite a lo t ' by vibration

Sites

Tring Mere Boughton Bridge Lewes East Grinstead Ludlow Leeds - A58 Leeds - A64

Per cent bothered 'very much ' or 'quite a lo t '

by vibration

Before

35 52

69 49 41 55 77 47


After

16 5 7 0

47 30 22 25 84

11

5.6 Effect of smoke and fumes

With the exception of pedestrians, the opinions of nuisance from smoke and fumes tended to be

lower than for the other nuisance factors (Table 7). Although there were substantial decreases in the

numbers of people claiming to be bothered by smoke and fumes between the 'before' and 'after' periods

(see Table 11), at the one site where fumes were measured the levels of various toxic substances in the air

were shown to be extremely low and not noticeably affected by the changes in the amount of traffic

(Table 4). Since fumes are not directly perceptible, even though smoke is visible, it is not surprising that

people's worries about smoke and fumes are poorly related to the actual measured levels of fumes. People's

worries would appear to be generated by assumption and association rather than by any evidence of fumes being present.

TABLE 11

Changes in percentage of people at home bothered 'very much' or '~luite a lot ' by smoke and fumes

Sites

Tring Mere Boughton Bridge Lewes East Grinstead Ludlow Leeds - A58 Leeds - A64

Per cent bothered 'very much' or 'quite a lot'

Before


16 16

41 31 17 27 30

7

After

11 1 0 0

24 12 9 5

43

5.7 Relation between general traffic nuisance and nuisance from particular factors

There is a suggestion in the results that feelings of nuisance from the specific factors - noise, smoke

and fumes, vibration, dust and dirt, and danger - may not be particularly highly correlated with the real

levels of these factors, but are highly correlated with the general expression of traffic nuisance (Table 1 la),

which in turn is highly correlated with the number of vehicles.

TABLE 11a

Correlation between individual nuisance factors and general traffic nuisance

Items

General nuisance and noise nuisance General nuisance and vibration nuisance General nuisance and dust and dirt nuisance General nuisance and smoke and fumes nuisance

General nuisance and traffic flow Noise nuisance and noise

Correlation coefficient

0.87 0.93 0.75 0.86

0.81 0.66

12

This type of attitude structure is known in social research as the 'halo effect', which means that if a

respondent is considering several attributes of an object, he will rate the individual attributes according to

his general impression rather than according to the attribute's own merits. For instance, if a respondent

generally dislikes something he will tend to score it unfavourably on all attributes.

In this particular study it was not possible to carry out physical measurements of all the factors

mentioned above; but nuisance from noise, for example, which was measured, had a correlation coefficient

of 0.87 with general traffic nuisance but only of 0.66 with actual noise levels. Similarly, nuisance from

vibration, and smoke and fumes, had a correlation of 0.93 and 0.86 respectively with general traffic nuisance.

It is not known what the correlation with the real levels of vibration, and smoke and fumes would be,

but on the limited evidence available of 'no change' in fumes at Tring (Table 4) and vibration perceptible

at only one of the three sites where measurements were made, and there for less than one per cent of the

time, it is extremely unlikely that high correlations between measured levels of the stimulus and expressed

levels of nuisance would have occurred.

These aspects of public attitudes may imply that in order to reduce traffic nuisance in streets of the

type surveyed it may be more important to reduce the flow of vehicles than to ameliorate the annoying

characteristics o f these vehicles. This does not mean that benefits could not be gained by improving

vehicle nuisance factors, but the perceptions of general nuisance from traffic may change less than such

physical improvements of single characteristics would suggest.

6. BEHAVIOURAL EFFECTS

6.1 Effects on particular activities

As well as causing unfavourable attitudes, traffic can also interfere with certain activities or make

their conduct more difficult. A check list of such activities was compiled for the study so that the effect

of traffic on these activities and the change between the before and after conditions could be monitored.

The percentage of people at home who said that they experienced such behavioural effects and the

change between the before and after studies are shown in Table 12. Highest on the list was the need to

keep windows shut at times when people would have preferred to have them open for ventilation. Next

came interference with sleep, particularly being woken up rather than in having difficulty getting to sleep.

Interference with television was also an effect fairly commonly attributed to traffic but the relation

of this item with the level of traffic flow was poorer than for many of the other items.

Correlation coefficients have been calculated for all the items listed in Table 12 against traffic flow,

the percentage of medium goods vehicles and the percentages of heavy goods vehicles. These coefficients

are shown in Table 13. In the before studies, where nuisance levels and traffic flow were fairly high, there

was no relation between these nuisances and the flows at the sites. Two of the items, 'being startled' and

'interference with conversation', were significantly correlated with the percentage of heavy lorries.

In the after studies many more of the items were significantly correlated with the level of traffic;

taking the before and after surveys at all the sites into account, all of the items were significantly correlated

with flow, the highest correlation being with sleep disturbance.

13

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Overall, several of the items were also well correlated with the percentage of heavy goods vehicles

but there was little association with the percentage of medium goods vehicles. For the combined analysis

of the before and after surveys almost as many factors correlated better with the flow of heavy goods

vehicles as correlated better with total traffic flow.

6.2 Severance

One of the possibly harmful effects of both roads and traffic is that they may cause some severance

of communities, either by suppressing some trips to facilities across the road or by making access to these

facilities more difficult. Crossing movements were not measured in this study but opinions of difficulty

in crossing were. This showed a positive correlation with the amount of traffic (r = 0.81) with only a very

slight increase in the variance explained (less than 2 per cent) when the number of heavy lorries was added

in a multiple regression analysis. The relation between traffic flow and crossing difficulty is illustrated in

Figure 5 which shows that 50 per cent of respondents do experience difficulty in crossing when flows reach

around 10,000 per 16 hour day.

7. SHORT TERM AS OPPOSED TO LONG TERM EFFECTS

A possible disadvantage of spending resources on some environmental improvements, is that as these

improvements tend to be subjective, a matter of opinion, people may quickly adapt to the new conditions

and in the end may be no more satisfied. It has been claimed that people value the conditions more highly

soon after a change than during more stable conditions. The data on respondents' valuation of noise effects

suggest that this may have occurred (Figure 6), but the difference between the before and after valuations

of nuisance for particular levels of noise was not statistically significant. As regards nuisance generally,

there was no evidence of people over-valuing the conditions after a change compared with in a more stable

state.

Further examination of the possibility of adaptation was made by carrying out a second after study

at Tring, amongst pedestrians only, one year and 3 months after the first 'after' study (Table t4).

TABLE 14

Long term changes

1 st After 2 months after

change

2nd after 1 year 3 months after

change

Per cent bothered by traffic 43 46

Per cent considering J A good thing 90 90 by-pass to be "~ A bad thing 3 5

Per cent considering conditions to be:

44 43 13

A lot better I A little better

No different A little worse A lot worse

38 46 13

2 1

16

Although there was a slight worsening in some of the indices the changes were not statistically

significant. This again suggests either no adaptation or a very slow adaptation effect.

8. RESPONDENTS" EXPECTATIONS

At all but the two smallest by-pass sites people's expectations of improvement were greater than they felt

actually occurred. At these two smallest sites (Bridge and Mere) traffic decreases were very large and

expectations were realised. Elsewhere, however, there were large statistically significant differences in

anticipated and realised benefits (Table 15).

TABLE 15

Expected improvements

Anticipated benefits: Realised benefits: Sites % saying conditions % saying conditions

would be 'a lot better' a r e 'a lot better'

Mere 81 84

Bridge 96 97

Lewes 88 72

23 Stafford 41

East Grinstead 65 49

Tring 76 53

These data were obtained by asking respondents in the 'before' studies how much better they

thought conditions would be after the by-passes had opened, and then, in the'after'studies, they were

asked how much better conditions were, now that the by-pass was open.

This phenomenon has also been observed in other studies 22, but in reverse, in that respondents'

worries about deterioration in environmental conditions were not fully realised. It may be explained

by a general attitude of people expecting policies or actions to have more effect than they actually do.

9. RELATION BETWEEN TRAFF IC AND NUISANCE TO PEOPLE AT HOME

9.1 Correlations - actual levels for people at home

One of the purposes of this study is to develop a method to predict the environmental effects and

public reactions in locations where future changes may be proposed. It is therefore important to establish

the relation between nuisance and flow, and also which parameters of traffic flow are most useful for

predictions of nuisance.

Four aspects of traffic were measured at all sites. These were the 16 hour flow, the number of heavy

lorries, the percentage of heavy lorries, and noise. Overall, taking both the before and after observations

into account, the best single indicator was the number of heavy lorries, but there was also a high correlation

with traffic flow and the percentage of heavy lorries in the flow. However in the before studies only, where

17

all the flows were at a fairly high level, the highest correlation coefficient was with the percentage of heavy

lorries (Table 16).

TABLE 16

Traffic and nuisance - residents' correlation coefficients

Relations Before After Both

Flow and nuisance

Per cent heavy lorries and nuisance

Number of heavy lorries and nuisance

Noise and nuisance

NS

0.81

0.68

NS

0.92

0.75

0.82

0.82

0.81

0.82

0.84

0.62

NS = not significant at the 5 per cent level

A multiple regression was carried out using the above variables. The simple regression of nuisance

on flow, for all the sites both before and after, is illustrated in Figure 7. The highest correlation (R = 0.92)

was obtained by using flow and heavy lorries in the equation:

y = 5.34 + 0.0025x 1 + 4.47x 2

where y -- percentage people bothered

x 1 -- 16 hour traffic flow

x 2 = per cent heavy lorries

The standard error is 10 percentage points.

The range of traffic flows encountered in the study was between 1000 and 16,000 vehicles per

16 hr day, with up to 11 per cent heavy vehicles. It would be unwise to extrapolate much beyond these

limits.

Similar predictions, not statistically inferior, can be made by substituting noise for total flow and/or

number of heavy lorries for percentage of heavy lorries. These alternative equations are shown in the

Appendix.

9.2 Relation between changes in nuisance and changes in flow

As well as using the actual levels of nuisance and flow it is also of interest to examine the changes

that have occurred and how they are related. In Table 17 the percentage change in the percentage

bothered by traffic has been correlated with the change in total traffic flow, the change in noise and

the change in lorry traffic.

18

TABLE 17

Correlations of changes

Correlation with change Traffic variables in nuisance

Change in number of vehicles

Percentage change in proportion of heavy lorries

Change in number of heavy lorries

Change in noise

0.84

0.90

0.85

0.81

There is a high correlation between the change in those four variables and the change in nuisance;

these correlations are higher than when the actual levels are used, presumably because particular local

influences are better controlled by this method.

The regression of change in flow and change in nuisance is shown in Figure 8, but the best prediction

is given by the multiple regression equation:

y = 28.1 + 0.05x I + 0.008x 2

where y =

x 1 ----

x 2

percentage change in nuisance

reduction in number of heavy lorries (16 hour flow)

reduction in total traffic (16 hour flow)

The multiple correlation coefficient is R = 0.96, with a standard error of 17 per cent.

Similar predictions (not statistically significantly different) can be made by substituting noise for

traffic and/or percentage of heavy vehicles for numbers of heavy vehicles.

10. CONCLUSIONS

By studying public reactions in a number of situations where traffic changes have occurred, mainly due to

by-pass construction, it is now possible to predict the likely reactions at sites where relief from existing

traffic conditions is proposed. Relations between a variety of nuisance and traffic measures have been

derived and prediction equations calculated.

Large improvements in environmental conditions have occurred in all the by-passed towns, but in

particular the smaller ones. There is a close correlation between town size and the amount of traffic

relief, and it is only in towns of less than 10 000 population that traffic decreases larger than 50 per cent

can be expected by by-pass construction.

Danger, noise, vibration, dust and dirt, and smoke and fumes were established as the main nuisance

factors, but the relative importance of each varied between the different groups of people surveyed,

ie pedestrians, people at home, shop workers and office workers. For people at home and office workers

19

the main nuisance was noise, for shop workers it was dust and dirt and for pedestrians it was danger from

traffic. Reactions to noise, vibration and fumes seemed better related to the traffic flow than to objective

measures of the impact. Thus to reduce traffic nuisance in streets of the type studied here it may be more

important to reduce vehicle flow than to ameliorate the annoying characteristics of the vehicles themselves.

Traffic effects on people's behaviour were also investigated. People reported they were affected in

a number of different ways by traffic, in particular being startled, having sleep disturbance and having to

keep windows closed.

People generally expected more improvement from the effects of by-pass construction than actually

occurred. It was only in the smallest towns that their expectations were fully realised. It has been suggested

that people value conditions soon after a change differently from when in a more stable situation.

Specifically they may overvalue an improvement in conditions. There is a possibility that this may have

occurred with opinions about noise nuisance but the data are not statistically significant. For traffic

nuisance generally there is no evidence of such overvaluation. Attitudes measured soon after the traffic

changes were similar to repeat measurements made more than a year later.

1 1. ACKNOWLEDGEMENTS

This report was prepared in the Access and Mobility Division of the Transport Operations Department of

TRRL, but a number of other people contributed to the study.

Thanks are due to Mr L J Griffin of the TRRL Assessment Division for some of the computer

analysis; to Mrs M Pattinson and her team of interviewers, Spencer Marketing and Mark Donaldson

Research for the interviewing fieldwork, to staff of the County Councils of Kent, Stafford, Shropshire,

East and West Sussex and West Yorkshire and Mr J Kember Smith of TRRL Highway Traffic Division

for supplying the traffic information; to Dr P M Nelson, Mr PAbbott and Mr N Godfrey of TRRL

Transport Engineering Division and Stafford Borough Council for supplying noise measurements and

to Mr D Colwill and Mr A J Hickman of the TRRL Assessment Division for supplying air pollution data;

and finally to Dr D J Martin, formerly of the TRRL Environment Division, for the vibration measurements.

12. REFERENCES

. LEITCH, Sir George. Chairman. Report of the Advisory Committee on Trunk Road Assessment. London, 1977 (H M Stationery Office).

. DEPARTMENT OF TRANSPORT. Policy for roads: England 1980. London, 1980 (H M Stationery

Office).

. DAWSON, R F F. Environmental effects of Alton By-pass. Department of the Environment, TRRL Report LR 589. Crowthorne, 1973 (Transport and Road Research Laboratory).

4. MACKIE, A M and L J GRIFFIN. Before and after study of the environmental effects of Tring

by-pass. Department of the Environment Department of Transport, TRRL Report LR 746.

Crowthorne, 1977 (Transport and Road Research Laboratory).

20

. MACKIE, A M and M FORSTER. Environmental effects of traffic in Ludlow, Salop. Department of the Environment Department o f Transport, TRRL Report SR 245. Crowthorne, 1978 (Transport

and Road Research Laboratory).

. MACKIE, A M and L J GRIFFIN. Environmental effects of traffic: case study at Mere, Wiltshire.

Department of the Environment Department of Transport, TRRL Report SR 428. Crowthorne,

1978 (Transport and Road Research Laboratory).

. MACKIE, A M and L J GRIFFIN. Environmental effects of by-passing small towns - case studies

at Boughton, Dunkirk and Bridge. Department of the Environment Department o f Transport, TRRL Report SR 349. Crowthorne, 1978 (Transport and Road Research Laboratory).

. HIGHLANDS AND ISLANDS DEVELOPMENT BOARD. The economic effect of by-passes on local

businesses. August, 1979.

9. OHIO DEPARTMENT OF HIGHWAYS. A by-pass economic impact study. March, 1970.

10. PRESCOTT-CLARKE, P. Keswick and Cockermouth By-passes. The Environmental Effects.

Report No. P 473, December 1977 (Social and Community Planning Research).

11. ROAD RESEARCH LABORATORY. Assessment of Priority for Road Improvements. Road Research Technical Paper No. 48. London, 1960 (H M Stationery Office).

12. DEPARTMENT OF THE ENVIRONMENT AND WELSH OFFICE. Building and Buildings.

The Noise Insulation Regulations 1975. Statutory Instrument 1975, No. 1763. London, 1975

(H M Stationery Office).

13. HARLAND, D G. Units for exposure and response to traffic noise. Department o f the Environment Department of Transport, TRRL Report SR 297. Crowthorne, 1977 (Transport and Road Research Laboratory).

14. DEPARTMENT OF THE ENVIRONMENT AND THE WELSH OFFICE. Calculation of road

traffic noise. London, 1975 (H M Stationery Office).

15. BEVAN, M G and A J HICKMAN. A mobile laboratory for measuring air pollution from motor

vehicles. Department of the Environment, TRRL Report SR 89 UC. Crowthorne, 1974 (Transport

and Road Research Laboratory).

16. HICKMAN, A J, D M COLWILL and M R HUGHES. Predicting air pollutant levels from traffic

near roads. Department of the Environment Department of Transport, TRRL Report SR 501.


17. DEPARTMENT OF THE ENVIRONMENT. Specifications for Road and Bridge Works.

TechnicalMemorandum H5/71. London, 1971 (H M Stationery Office).

2 1

18. MARTIN, D J, P M NELSON and R C HILL. Measurement and analysis of traffic induced vibrations

in buildings. Department o f the Environment Department of Transport, TRRL Report SR 402.


19. MARTIN, D J. Low frequency traffic noise and building vibration. Department of the Environment Department o f Transport, TRRL Report SR 429. Crowthorne, 1978 (Transport and Road Research Laboratory).

20. INTERNATIONAL ORGANISATION FOR STANDARDISATION. Draft proposal. Vibration and shock limits for occupants in buildings (Amendment ISO - 2631), ISO/TC 108/SC4.

21. ROSMAN, P F. Subjective responses to the environmental effects of traffic in real life and simulated

environments. Department of the Environment Department of Transport, TRRL Report LR 911. Crowthorne, 1980 (Transport and Road Research Laboratory).

22. PRESCOTT-CLARKE, P. People and roads in the Lake District: a study of the A66 improvement

scheme. Department o f the Environment Department o f Transport, TRRL Report SR 606. Crowthome, 1980 (Transport and Road Research Laboratory).

22

100

I. ~ 6 0 -

"0

g

40 - • -

20 -

- . - -== m Desk study 8

' By-pass and relief road da ta*

y = aebx

y = 79.82e-O.00004511x

r -- 0.91

0 I I I I

0 10,000 20,000 30,000 40,000

Town populat ion

50,000

*Excludes Stafford where traf f ic management measuresifurther decreased ~ the f l ow

Fig.1 E f f e c t o f t o w n size on decrease in t r a f f i c f l o w a f t e r by-pass o r r e l i e f r oad road c o n s t r u c t i o n

--14

Predicted change dB(A)

--12 -10 --8 --6 - 4

I I I I l

/

- 2 0 2

/

/ / -

/ /

/ . / /

/

2

-2

-4

- 6

- 8

-10

-12

-14

-16

A <~ v r n

"O ¢D ¢31

0 l J~

no P == ¢o

Fig. 2 Comparison of measured and predicted changes in the level of L 10 dB(A)

"o 1.5 P

"5 r -

E O

.~_ co

C

r -

1.0

0 . 5 -

0 0

Fig. 3

y = a + b x y = 0.227 + 0.0584x r = 0.81 •

I I I

5 10 15 Change in noise levels, LlO dB(A)

Association of change in noise levels wi th noise nuisance to people at home rated on a 4 point rating scale

80

r j

80

"O .=

o

~ 40

.c

= 2O

0

y = a + b x y = 0.1446 + 4.63x A ~

m

• I I I 5 10 15

Change in noise level (dBA)

Fig.4 Association of change in noise levels wi th percent o f residents bothered by t raf f ic - by-pass sites only

100

80

o 60

E

r -

~ 20 a.,

0 0

y = 8.7 + 0.004216 x (r = 0.81) Plotted below • _ [y = 9.4 + 0.0039 x (flow) + 0.0056z (No. of heavy lorries)

(r = 0.82)]

• I I , I I I I I 2000 4000 6000 8000 10000 12000 14000

16hrtrafficflow

16000

Fig. 5 'D i f f i cu l t y of crossing' and f low

A ¢Lt

m ¢O

O ) ¢-.

P

0 ~ O O.

o

._== O c -

E 2

¢ J

Z

m

1 --

0 55

• Before I 0 After

S 0

I I i f I 60 65 70 75 80

Measured noise (18hr L10dBA)

Fig. 6 Nuisance f rom noise vs measured noise(By-pass sites only)

85

¢- oJ

¢D O.

100

90

80

70

60

50

40

30

20

10

0 0

Equation:- y = a + b x y -- 8.91 + 0.00395x R = 0.81

• Before • After

0 Leeds

- f

® ®

® o•

®

I I I 5000 10000 15000

16hr traffic flow

Fig. 7 Percent o f residents bothered by t ra f f ic vs 16hr t ra f f ic f l o w

\

- 1 0 0

Percentage change in flow

I I i I

Equation:- y = a + b x y = 26.0 + 1.4x r = 0.84

0 +20 +100

¢o

t - o ~

03

0 " ¢u ¢-

¢D ¢B

e- ¢D u= ¢D

O .

- 100

Fig.8 Percentage change in residents bothered by traffic vs change in 16hr traff ic f low (expressed as a percent of f low before the change)

13. APPENDIX

ALTERNATIVE EQUATIONS FOR PREDICTING THE LEVEL OF NUISANCE

(a) using 16-hour flow and number of heavy lorries

y = 14.4 + 0.002x 1 + 0.027x 2

where y ~ per cent of residents bothered by traffic

x 1 = 16-hour traffic flow

x 2 = 16-hour flow of heavy lorries

standard error = 12 per cent

R = 0.89

(b) using noise and per cent of heavy lorries

y = - 1 0 5 . 5 + 1.8x I + 5.77x 2

where y ~ nuisance

x 1 ~= no i se (18hr L10dB(A))

x 2 = per cent heavy lorries

standard error = 12.5 per cent

R-- 0.87

(c) using noise and number of heavy lorries

y = - 9 3 . 2 + 1.97x I + 0.035x 2

where y ~- nuisance

x 1 ~ noise(18 hr L10 dB(A))

x 2 = number of heavy lorries

standard error = 12 per cent

R = 0.89

29

(1826) Dd8041301 1,400 I0/81 HPLtdSo'ton G1915 PRINTED IN ENGLAND

ABSTRACT

Environmental effects of traffic changes: A M MACKIE and C H DAVIES: Department of the Environment Department of Transport, TRRL Laboratory Report 1015: Crowthorne, 1981 (Transport and Road Research Laboratory). The report describes a study of the environmental effects of traffic and traffic changes in nine towns where changes in traffic flow had occurred due to by-pass construction or traffic management schemes. An assessment of the nuisance caused by particular traffic flows has been made. The study also examined the effects of noise and air pollution on people's sensitivity to traffic. Nuisance was measured by means of personal interview surveys of people at home, pedestrians and people working in shops and offices. Nuisance levels changed considerably when the traffic levels changed.


ISSN 0305-1293

ABSTRACT

Environmental effects of traffic changes: A M MACKIE and C H DAVIES: Department of the Environment Department of Transport, TRRL Laboratory Report 1015: Crowthorne, 1981 (Transport and Road Research Laboratory). The report describes a study of the environmental effects of traffic and traffic changes in nine towns where changes in traffic flow had occurred due to by-pass construction or traffic management schemes. An assessment of the nuisance caused by particular traffic flows has been made. The study also examined the effects of noise and air pollution on people's sensitivity to traffic. Nuisance was measured by means of personal interview surveys of people at home, pedestrians and people working in shops and offices. Nuisance levels changed considerably when the traffic levels changed.


ISSN 0305-1293

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