Personal noise ranking of road traffic: Subjective estimation versus physiological parameters under laboratory conditions

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Abstract

Objective

To evaluate the subjective estimation of noise-induced discomfort and its correlation to psychoacoustic and physiological parameters under laboratory conditions. To establish an effective description of sound qualities of road traffic noise, supplementing the current standards and calculation specifications.

Methods

Pass-by vehicle noise samples were binaurally recorded with a dummy head measurement system, and synthetically composed to six vehicle ensembles considering different road beds, varying speed profiles and noise barriers. Fifty-one persons were selected and tested under laboratory conditions. Study participants were exposed to defined acoustic stimuli, alternating with neutral phases lacking acoustic content in a listening room. Concomitant recording of electrocardiogram (ECG) and respiratory rate was performed. Subjective estimation of noise-induced discomfort of assigned vehicle ensembles was rated on a personal ranking scale (PRS) by the study subjects. Subjective ratings were combined with objective psychoacoustic parameters by multiple regression analysis.

Results

Heart rate was increased during all noise exposure phases compared to neutral phases; the increase of heart rate differed among vehicle ensembles and was statistically significant in two cases (p<0.01). Respiratory rate remained unaffected. Personal rankings also differed among vehicle ensembles and correlated well with objective psychoacoustic parameters (p<0.0001); e.g., loudness combined with roughness describes the correlation with subjective estimation of noise-induced discomfort better than the A-weighted sound level. Vehicle ensembles rated more unpleasant caused higher increases in heart rate as well (p<0.0001).

Conclusions

The sound quality of road traffic noise as it is described by various psychoacoustic parameters not only determines the subjective estimation of noise-induced discomfort but in addition affects physiological parameters like heart rate. This should be considered for future perspectives in road- and traffic planning and therefore may serve construction engineers as well as traffic planner as a supplemental tool.

Introduction

In a time of intensified efforts towards environmental protection, especially the protection from “unwanted sounds” has become crucial. Not only the avoidance of hearing damage, which only occurs during high sound levels or long persisting acoustic irradiation, but also the impairment of the human well-being for instance caused by road traffic noise has to be considered. Road traffic noise, which is steadily increasing, is regarded as an important environmental health problem, the role of road traffic noise as stressor has also been brought up and was extensively investigated (Babisch et al., 2005; Babisch, 2002, Babisch, 2005; Bluhm et al., 2004; Griefahn et al., 2000; Jarup et al., 2005; Ouis, 2002). Moreover, disturbances of intended daily-live activities such as communicating, concentrated working, relaxing and sleeping occur even at low noise levels (Griefahn, 2002; Maschke et al., 2004; Ouis, 1999). This results in sustaining noise-induced discomfort, and in the long run may lead to further severe health effects like cardiovascular disease and an increased myocardial infarction risk (Babisch et al., 2005; Babisch, 2000; Ising et al., 1999).

The subjective estimation of noise-induced discomfort can be predicted only with difficulty in general (Morgan and Dirks, 1974). The informational quality of a certain sound like semantic or pragmatic aspects plus the intentional attitude of a person are highly situation-specific and therefore cannot be modelled in a reliable way. Thereby, fuzzy mathematical soft-computing methods describing the relationship between noise-induced discomfort and objective noise parameters are important to consider as reported previously (Botteldooren and Lercher, 2004).

Noise, once recognized by the human hearing, causes certain reactions. These reactions depend on signal characteristics like sound pressure level, frequency spectrum, stationary conditions and duration (Hellbrück et al., 2001; Moore, 1996). They also depend on physical and psychological conditions as well as on the current activity of the individual (Babisch et al., 2003). For the classification of sounds, independent perceptual base items such as loudness, roughness, sharpness, tonality and fluctuation strength are used by the human auditory system (Zwicker and Fastl, 1990). Modelling and combining these psychoacoustic parameters lead to an objective sound quality and are uninfluenced by the individual (Widmann, 1992; Zwicker, 1991). This can be tested under laboratory conditions if study participants are not able to allocate the presented acoustic source and in addition the sounds are lacking information content. The noise-induced discomfort is finally caused exclusively by the presented sound signal, the test subjects participate thereby under strict defined attempt conditions.

Therefore, an effective description of noise-induced discomfort can only be achieved by considering the characteristics of the human hearing including emotional aspects. At present, according to the current standards and calculation specifications, the impact of road traffic noise is represented by the A-weighted equivalent mean average sound level (LA,eq). In our opinion, this dimension considers too little the subjective estimation and evaluation of sound events by the affected and thus needs to be adjusted.

The study presented here was a co-project between the Institute of Highway Engineering and Transportation Planning, Graz University of Technology, the Institute for Electronic Music and Acoustics, University of Music and Dramatic Arts Graz, the Institute of Hygiene, the Institute of System Physiology and the Neurotology Department, ENT Clinic, Medical University Graz.

Section snippets

Setup of the study

In a first step, different roadbeds which are most commonly found on Austrian highways were determined and selected for sound recordings (data source kindly provided by ASFINAG, the Austrian Highway Financing Company). Out of these various roadbeds, three different types were chosen: concrete (C), asphalt-concrete (AC) and split-mastix-asphalt (SMA). The pass-by noise of different passenger cars and motor trucks with variable speed profiles on each of these roadbeds were binaurally recorded

Results

To select a homogenous and healthy study collective, prior existing hearing damages had to be ruled out. Answering of an elementary standardized questionnaire by the study subjects was also obligatory. All 51 study subjects included in this study were tested by audiometry and showed normal audiograms (data not shown). The standardized questionnaire employed herein reflected on the one hand the study participant's subjective estimation of being disturbed by road traffic noise by day and night

Discussion

Traffic noise, in particular road traffic noise represents one of the most interfering effects frequently mentioned in relationship with environmental stressors (Schreckenberg and Guski, 2005). At present, the impact of traffic noise is represented by the A-weighted equivalent mean average sound level (LA,eq) only. However, loudness of a sound event is caused by complex reciprocal effects of frequency components and their temporal development, resulting in the fact that sounds with identical L

Acknowledgements

This multidisciplinary project was financed by ASFINAG, the Austrian Highway Financing and Operating Company, by the Austrian Federal Ministry of Agriculture, Forestry, Environment and Water Management (BMLFUW) and the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT).

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