Investigation and analysis on noise levels in metro carriages in a city

Background A running metro train produces intense noise, which may not only reduce passengers' comfort in carriages, but also adversely affect their psychological and physical health to varying extents.

Objective This study is designed to assess the noise levels in metro carriages and explore the effects of passenger flow and station broadcast on the noise levels in a city.

Methods The noise levels in the carriages of 10 metro lines in the city were measured with a noise dosimeter from 7:00 to 15:00 on weekdays from 15-28 November, 2018, and the equivalent continuous A-weighted sound pressure levels (L_Aeq) of total measuring time (8 h, from 7:00 to 15:00), peak (from 7:00 to 9:00) and off-peak (from 9:00 to 15:00) time, broadcast and nonbroadcast time were calculated for each line respectively. Paired t-test was applied to compare the L_Aeq between peak and off-peak time and between broadcast and non-broadcast time.

Results The mean 8 h L_Aeq in the detected carriages of the 10 metro lines ranged from 74.6 to 80.9 dB (A). The mean L_Aeq of peak time and off-peak time were 74.7-81.1 dB(A) and 74.4-80.8 dB(A), respectively, and no significant difference was observed between the two time periods (t=-1.564, P=0.125). The mean L_Aeq of broadcast and non-broadcast time were 74.2-80.7 dB(A) and 74.7-81.2 dB(A), respectively, and no significant difference was observed between the two time periods (t=-1.640, P=0.102).

Conclusion According to the exposure limit recommended by the US Environmental Protection Agency and the World Health Organization, the risk of hearing loss is relatively low for the passengers on the 10 metro lines in the selected city. Passenger flow and broadcast may not have substantial effects on the noise levels in metro carriages.