Public Health Impacts From Subway Noise: Case Study Hong Kong MTR
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Date
February 3, 2020
Author(s)
Xu, Stephany
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Citation
Xu, Stephany. 2019. Public Health Impacts From Subway Noise: Case Study Hong Kong MTR. Master's thesis, Harvard Extension School.
Abstract
The significance of the research is to measure and quantify the potential noise induced health risks to passengers riding the Hong Kong MTR subway system with the objective to provide recommendations for reducing noise exposure. Subway noise can range from 80-112 decibels (dB), which greatly exceed the 70dB level set by the World Health Organization (WHO) and EPA for safe environmental noise levels (Gershon, Neitzel, Barrera, & Akram, 2009). While the effects of noise are rarely detrimental, single events above 110 dB or cumulative exposure above 80-85dB can lead to noise induced hearing loss (NIHL), and other indirect health impacts such as cardiovascular disease, sleep disturbance, cognitive impairment and hypertension (Basner, Davis, Clark, & Stansfeld, 2014).
The main question to be answered is: What are the potential public health risks from riding the Hong Kong subway? Given that the threshold for environmental noise given by the EPA and WHO is 70dBA the following hypothesis are tested:
● Average noise exposure during peak-hours (rush hour) is 5dBA higher than off- peak hours (non-rush hours).
● Commuters who ride the subway for 2-hour or more are being exposed to noise levels of >=80dBA and are at risk of developing NIHL.
● The burden of disease (BOD) from subway noise exposure on the average commuter is 25% of the occupational noise exposure in Hong Kong.
Noise sampling is done across all subway lines and stations of Hong Kong MTR from inside the train car and on the platform. An overall noise map of the subway system and spectral analysis is done to understand the direct and indirect health impacts of the noise on the human body and estimate the associated BOD. Finally, a preliminary exploration of sound-to-speed relationship is carried out to understand the potential for noise reduction.
The results of the study show that the average Hong Kong MTR train ride has a Leq of 74.1 dBA and Lpeak of 100.9dBA. The Island Line is the loudest with in-train noise average of 81.7dBA and peak of 108.1dBA. Underground and enclosed tunnel sections are significant contributor to high noise levels, by about 10dBA, due to reverberation, and low frequencies account for the majority of the sound pressure source.
The average MTR commute can add 8dBA to the overall environmental noise exposure, and bring the overall noise level exposure in a day from 59.5-75.2dBA to 67.5- 75.6dBA. Passengers riding for 2-hours a day on the MTR have increased risk of developing NIHL, as at L10 the exposure is above 85dBA and the estimated BOD (burden of disease) can be up to 99 DALYs (disability adjusted life years) from direct noise exposure. The risk of indirect health impacts from MTR noise account for the majority of the BOD, such as annoyance, hypertension and increase cardiovascular disease, and can be up to 277,086 DALYs.
The preliminary sound-to-speed show that reducing the top speed of the train by allowing for a longer cruising time at lower speeds could be an effective way to reduce noise without costly investments in sound absorbing materials. An increase in overall transit time of 10% could yield a 50% drop in sound pressure.
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