The U.S. mass transit system, the largest in the world, generally is generally considered one of the safest modes of travel, but recent public health studies have identified several sources of environmental hazards with it, including excessive noise, a large and growing problem in urban settings.
Confirming that hazard is a team of researchers from the University of Washington and Columbia University, who found that Metropolitan Transit Authority subways had the highest average noise levels of all mass transit in New York City, with levels high enough to increase the risk of noise-induced hearing loss.
Researchers studied the risk of excessive exposure to noise related to mass transit ridership and conducted an extensive set of noise measurements of New York City mass transit systems. The findings were posted online today in the American Journal of Public Health and will be published in the Journal's August issue.
Noise-induced hearing loss, a permanent, irreversible health problem, is estimated to affect more than 30 million people worldwide, including as many as 10 million in the United States.
Using sensitive noise dosimeters, the team of researchers conducted hundreds of measurements of noise levels at platforms and stations, as well as inside of vehicles on New York City subways (MTA and PATH), buses (MTA), ferries (Staten Island), commuter railways (LIRR, SIRR and Metro North), and the Roosevelt Island tramway.
The scientists found that, on average, the MTA subways had the highest noise levels, at 80.4 decibels (dBA), followed by the Path trains, at 79.4 dBA, and the tram, at 77.0 dBA. The lowest average levels measured, 74.9 dBA and 75.1 dBA, were obtained from the LIRR and Metro-North trains, respectively.
The very highest levels measured in the study were found on an MTA subway platform (102.1dBA) and at a bus stop (101.6 dBA).
In contrast, the noise level of a whisper is 30 dBA, normal conversation is 60 to 70 dBA, a chain saw is 100 dBA, and gunfire is 140 dBA.
The U.S. Environmental Protection Agency and the World Health Organization recommend daily exposures of no more than 70 dBA for a 24-hour average. Noises that register below 70 dBA generally have no impact on hearing health and don't cause people to exceed the daily recommendations.
But for many people, "unless the noise is also considered to be a nuisance, such as noisy neighbors late at night, exposure to most loud noise levels is often not perceived as potentially hazardous, and precautions are rarely taken," a researcher said. "People do not necessarily pay attention, for example, to excessive noise from attending concerts, riding motorcycles or even listening to MP3 players at high volume for extended periods."
Excessive noise exposure also is linked to hypertension, heart disease, disruptions in stress hormones, and sleep disorders, and it has been shown to interfere with learning in children, the researchers said.
For these reasons, the scientists said noise control efforts, including increased transit infrastructure maintenance and the use of quieter equipment, should be a priority.
They also underscored the need for personal protection, although they noted that music headphones and earbuds generally do little to reduce noise exposures. In fact, they said, such devices often increase exposures, as users turn the volume of MP3 players up higher than normal to drown out surrounding noise.
But a variety of earplugs and earmuffs are commercially available, most of which would be sufficient to reduce transit noise exposures to below the recommended limits, they said.
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