Monitoring and assessment of daily exposure of roadside workers to traffic noise levels in an Asian city: a case study of Bangkok streets.

Four noise monitoring sites were strategically established to evaluate average noise level and audiometric assessment at various traffic zones of Bangkok Metropolitan Region (BMR). During the monitoring period, noise levels were found to be 72.8-83.0 dBA during day time and 59.5-74.5 dBA during night time. The finding also indicated that traffic noise levels depend on distance from roadside, diurnal variation and character of the traffic and street configuration. Audiometric measurement of 4000 persons was carried by four major hospitals in Bangkok to study the relationship between traffic noise exposure of groups of people working in the streets and hearing loss. Four different categories of occupational people, i.e., drivers, street vendors, traffic officers and dwellers were selected and were further classified into age groups (16-25, 26-35, 36-45 and 46-55 years old) to monitor the traffic noise induced hearing loss throughout their everyday lives. The control group was deliberately chosen to screen out the effects of traffic noise. According to the audiometric investigation, it was revealed that hearing capacity of the daily noise exposure groups living in the three urban sites (Yaowarat Road, Din Daeng Road and Ratchaprarop Road) were noticeably poorer than those who were living in suburban site (Phahonyothin Road). It was noted that the mean hearing threshold level (HTL) of the 16-25 years old groups were found to have better hearing capacity than those older adults of 46-55 years old. In particular the mean HTL dropped at the frequency of 4000 Hz. Among the occupational population who were living in the urban monitoring sites, the driver groups were found to have the highest risk of traffic noise induced hearing loss.