Also, excessive noise exposure is a serious global urban health problem, adversely affecting millions of people. One often cited source of urban noise is mass transit, particularly subway systems. Both existing and future noise levels in the study area are relatively high at almost all locations in the study area during almost all hours of the day.
They reflect the fact that traffic volumes throughout the study area are high, with relatively high truck and bus volumes. Platform doors could also improve service because train operators would not have to slow down as they approach crowded platforms, and they could reduce litter on the tracks, which can set off fires and cause delays.
Noise exposure is a function of 2 main factors:
(1) the frequency-weighted exposure level, measured in A-weighted decibels (dBA), and
(2) the exposure duration. The causal association between chronic exposure to excessive noise and permanent, irreversible, noise-induced hearing loss (NIHL) is well known, as are the adverse social, psychological, and occupational effects associated with the condition.
Nonauditory adverse health effects have also been reported, and recent research suggests that excessive noise exposure may be linked to hypertension and ischemic heart disease, disruptions in stress hormones, and sleep disorders.
