Cabin Noise of Metro Systems in Various Cities.

Metro systems are typically regarded as a means to transport a large number of commuters in a relatively short duration, reduce reliance on cars, and as a means to mitigate traffic congestion, reduced air and noise pollution for a better living environment. Most of the metro systems are either underground in densely populated area to free up the land on the surface for other economic developments or open space for enhancing the quality of life. Some metro systems are also on elevated viaducts especially for the outskirts of cities or in cities for overcoming congested traffic junctions. Noise exposure in metro cabin has become a concern with increased use and extended networks of metro systems as commuters may be exposed to the noise for an extended duration. In this study, the measurement of the cabin noise of various metro systems around the world was carried out using a smartphone with the built in microphones calibrated against a typical type 1 sound level meter using our in-housed developed app. The cabin noise of metro systems for five cities in Asia and Europe was measured on various occasions. The cities are London, Prague, Paris, Singapore and Taipei. We found that the average noise level for all metros were well below 85 dB and therefore traveling on these metro systems for eight hours was not likely to exceed the maximum duration of noise exposure under the National Institute for Occupational Safety and Health (NIOSH) guidelines. We also found that average sound pressure level in dBC was about 6 dB higher when compared to dBA. This indicates the presence of low-frequency components below 200 Hz.