These older systems were designed before noise-control technologies were available. 19– 21 Five of the US systems are more than 75 years old, and the largest, the New York City subway system, with over 4 million riders per weekday, 22 is more than 100 years old. 18 There are 14 subway systems in the United States, with a combined daily ridership in excess of 10 million people. The US mass transit network, with an infrastructure encompassing subways, buses, commuter and light rail, ferry boats, trolleys, and tramways, is the largest in the world, with 9.7 billion passenger rides in 2006. The size of the population exposed to mass transit noise is of considerable magnitude. Therefore, nonoccupational sources of exposure are coming under scrutiny, including mass transit. 16, 17 Importantly, even though US occupational exposure regulations have been in place for decades, rates of NIHL-related workers' compensation cases remain high. 14, 15 The limited data available suggest not only that NIHL prevalence and incidence rates are extraordinarily high but also that the associated costs are enormous. 14 Hearing loss from all causes ranks among the top 10 most common serious health problems worldwide, and NIHL is the leading occupational disease in industrialized nations. 13 In the United States alone, between 3 to 10 million people are estimated to have NIHL. Worldwide, more than 250 million people are estimated to suffer from hearing loss, of which at least 30 million cases represent NIHL. There are no comprehensive national or international surveillance programs for hearing loss. Nonauditory adverse health effects have also been reported, 6– 8 and recent research suggests that excessive noise exposure may be linked to hypertension and ischemic heart disease, disruptions in stress hormones, and sleep disorders. 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.
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. 3– 5 A particular concern is the potential for mass transit to result in excessive exposure to noise. 2 Although there are well-documented environmental and public health benefits associated with mass transit, interest in the health and safety effects of mass transit on urban communities is increasing. For example, in 2004 there were 95 subway systems worldwide today there are 167, a 76% increase in only 5 years. 1 An important factor supporting the growth and viability of urban centers is mass transportation, which is rapidly expanding to keep pace with increasing demand. Environmental noise–control efforts in mass transit and, in cases in which controls are infeasible, the use of personal hearing protection would benefit the ridership's hearing health.įor the first time in history, more than half of the world's population lives in cities, and it is projected that more than two thirds of the population will live in cities by 2030. Mass transit noise exposure has the potential to exceed limits recommended by the World Health Organization and the US Environmental Protection Agency and thus cause noise-induced hearing loss among riders of all forms of mass transit given sufficient exposure durations. All transit types had L eq levels appreciably above 70 A-weighted decibels, the threshold at which noise-induced hearing loss is considered possible.Ĭonclusions. Of the transit types evaluated, subway cars and platforms had the highest associated equivalent continuous average (L eq) and maximum noise levels. We used noise dosimetry to measure time-integrated noise levels in a representative sample of New York City mass transit systems (subways, buses, ferries, tramway, and commuter railways) aboard transit vehicles and at vehicle boarding platforms or terminals during June and July 2007. We measured noise levels associated with various forms of mass transit and compared them to exposure guidelines designed to protect against noise-induced hearing loss.
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