Levels of Annoyance During the Reference Day and Night Periods

The sample considered in this section refers to those households who said that either day or night is noisy or very noisy. The number o f households annoyed in each reference period is represented in Table 6.20.

Table 6.20: Households Annoyed During the Day and Night Reference Noise Periods.

Levels o f Annoyance Day Night

1. Very much 80 82

2. M oderately 69 76

3. A little 15 23

4. Not at all ^{1 1}

Total 165 182

*Missing data: 12 cases.

❖ Correlation between noise ratings (very noisy: noisy) with Levels of Annoyance during the day (N=165): Kendall’s tau correlations is represented in Table 6.21. Kendall’s i (tau) = 0.635 (p=0.000; p<0.01). Therefore noise ratings are strongly correlated with levels o f annoyance.

Table 6.21: K endall’s tau b Correlation between Noise Ratings and Levels o f Annoyance during the Day.

Correlations

NLD LAD

Kendall's tau b NLD Correlation Coefficient 1.000 .635"

Sig. (2-tailed) .000

N 165 165

LAD Correlation Coefficient .635** 1.000

Sig. (2-tailed) .000

N 165 165

*’ ■ Correlation is significant at the .01 level (2-tailed).

*1* Correlation between noise ratings (very noisy: noisy) with Levels o f Annoyance during the night (N=182): Kendall’s tau correlations is represented in Table 6.22 i (tau) = 0.510 (p=0.000; p<0.01). Therefore noise ratings are strongly correlated with levels of annoyance during the night.

Table 6.22: K endall’s t a u b Correlation Between Noise Ratings and Levels o f

**• Correlation is significant at the .01 level (2-tailed).

Considering the different sample sizes in each annoyance group (day versus night), a noise disturbs them more, they stated as main disturbance effect during the day (7am-10pm)

“difficulty in resting/falling asleep” (78 cases) and during the night this answer was given

LAD - LAN Negative Ranks 19a 20.89 397.00

Positive Ranks 18b 17.00 306.00

also by the majority (54 cases). Only 21 households ( 8 were for the day period) have considered noise as causing frustation and irritation.

In the study area 93% o f the sampled individuals said traffic noise was the most important cause of disturbance in their homes. 1.6% and 1.3% o f the respondents referred noise from neighbours and construction, respectively. As this question was posed near the end o f the questionnaire, it can be concluded that traffic noise was the main source o f noise. This was expected from the preliminary selection o f the study area, taking into account its characteristics. The SP experiment is set to value noise traffic externalities in the home.

6.8 CO NCLUSIONS

The main descriptors o f the sample o f households and respective context were comprehensively analyzed. The statistical analysis is a useful base for the subsequent modelling chapters (when it will be assessed the nature and extent o f householders’

preferences for quiet indoors) in order to assure consistency with sample characteristics. This will serve as additional criteria for assessing the theoretical plausibility o f the models.

Moreover, for future noise studies using a similar SP experimental design, but conducted in different locations, this analysis will provide a rich basis for a consistent comparison of values o f quiet (noise) across different circumstances.

The residential area selected as pilot showed to have a very satisfactory diversity in terms of their inhabitants, buildings and apartment characteristics. The sample is representative of the average and higher incomes groups, and it is under-represented in the lower income range. It shall be noted that the Lisbon Metropolitan area (LMA) has the highest socio-economic indicators in the country. The purchase power index is 155 for the LMA whereas this value is 100 for the whole country. On the other hand, considering the 18 councils that comprise the LMA, Lisbon has a purchase power index around four times higher than the average (INE 2000). The sample o f respondents had higher education levels than the country average, and most households accepted well the computer survey.

The range o f noise measurements outdoors (ground floor) at the front and back fapades of the buildings showed a very small variation in the situations where noise barriers had been installed. The range o f indoor (outdoor) noise measurements taken at each apartment floor had a larger range of variation. This reflected the wide variety o f buildings and situations (terrain elevations, noise barriers, facade parallel, height o f buildings, etc). Considering that

the buildings surveyed were all in the vicinity o f the main roads, the effect o f distance to road is highly correlated with floor number.

Considering the WHO guidelines for dwelling indoors (30-35 dB(A)) to prevent moderate annoyance and to affect on speech intelligibility during the daytime and evening period, it was shown that 243 households (59% of the sample) had noise levels greater than Leq 35 dB(A). As 93 % o f the sampled individuals reported road traffic was the main disturbance factor, it can be concluded that traffic externalities manifest themselves in the home by reduced levels of acoustical comfort.

Individuals’ perceptions of the internal noise levels and the existence o f a quieter-noisier facade plays a central role in the SP- choice experiment. In the sample of respondents, correlations o f perceptions with the physical noise measures were higher for relative measures (difference in levels relative to the situation experienced in respondent’s apartment). The Independent samples t-test shown than respondents perceived upper floors as noisier than lower ones in terms of mean perceived levels. This fact was in agreement with the real mean variation in Leq dB(A). This is consistent with the topographic and physical characteristics o f the study area and noise barriers in situ.

Relative ratings could be related with the relative physical noise measures in Leq dB(A).

However, the multiple regression models estimated with higher fit with the data showed that the variables that were statistically significant were only a few: exposure at the back facade, apartment choices within the same lot o f the respondent, floor number and height of building. The explanatory power of the relationship was not high, and this fact limits the applicability o f the model outside the present context.

The Wilcoxon signed rank test showed that there is a statistically significant difference for the ratings given for the night and day reference periods. The reference day period (7am- 10pm) is considered noisier. This finding is consistent with the traffic patterns identified:

main roads are used for commuting into Lisbon, whereas traffic levels are substantially lower during the night (pm peak traffic flows are typically lower than in the am peak, Appendix 2). Kendall’s tau statistical test showed that mean noise ratings at the extremes o f the scale (“very noisy”, “noisy”) were highly correlated with the annoyance levels both during the day and night noise reference periods. This issue can be the subject of further investigation in the future in community noise studies.

CHAPTER 7: