Study on quantification of stress according to sound pressure level of road noise: Case of salivary cortisol and heart rate

Drivers are continuously exposed to various types of driving noises such as road noise, wind noise, and exhaust noise. Road noise is the most frequently encountered among these. It can cause cardiovascular diseases, auditory hallucination, and insomnia in drivers. Therefore, research should be conducted to identify appropriate analysis methods for quantifying stress caused by road noise to prevent its hazardous effects. The purpose of this study was to identify an appropriate method for analyzing psychological loads such as road noise through hypothesis testing by conducting hormonal evaluation and electrocardiogram (ECG) analysis. In addition, the relationship between specified road noise levels and cortisol secretion or heart rate was analyzed. Saliva samples were collected from participants for hormonal evaluation, and the heart rates were measured for ECG analysis. For an accurate hormonal evaluation, saliva samples were collected two times from 20 participants (17 male and 3 female) with a mean age of 26 years (SD: 3.07). During the noise evaluation, the participants were exposed to sound pressure levels (SPLs) of 50, 60, and 70 dB. A 40 min break was permitted between noise levels. Saliva samples were collected in the afternoon (13:00–15:00) considering the cortisol circadian rhythm. In this study, a saliva collection kit and detection kit were used for the cortisol analysis, and an electrocardiometer was used to measure the participants’ heart rates. The analysis results revealed the hormonal evaluation to be more significant than the ECG analysis for quantifying the stress induced by psychological loads such as road noise.