The Noise Problems of Public Transit

ABSTRACT

This study shows noise levels of CTA Brown Line and recommendations for noise reduction in Central Business District, residential areas and retail areas. Noise levels in Brown Line are serious problems like environmental pollution, when trains passed to measuring points. Noise levels (LAeq) were 79.4 ~ 87.5 dB depending on geographical aspects. Also maximum noise levels (LAMax) were 84.2 ~ 93.0 dB when trains passed.

There are several methods to mitigate noise levels depending on land use and circumstances of areas. Barriers, vegetation, buffers, setbacks, site design, unit design, building design and building facades can be applied to individual areas. So we can expect reduction of noise levels in ambient residential buildings and houses near Brown Line railroads. What expectations of reduction of noise levels if the methods are implemented are considered is 5.0 ~ 25.0 dB depending on different methods.

INTRODUCTION

After the Industrial Revolution, human beings had focused on developing material prosperity without concerning quality of life. Also we did not know that there are negative sides in visible and invisible value of human life due to material prosperity. After we have recognized those facts, human life has been strived to bring in relief from focusing on developing.

During the last 20 years, there has been increasing concern with quality of the environment. Noise has been recognized as one of the serious pollution along with air and water pollution. As industry has been developing, noise levels have risen and have become badly effect to human beings.

The definitions of sound and noise are different. Noise is defined that a sound, especially it is loud, unpleasant or disturbing. Noise affects adverse influence to people and the environment as well as other physiological and psychological problems. Besides, noise disrupts communication and individual life.

Noise emanates from many different sources such as transportation noise, industrial noise, construction noise, household noise and people and animal noise.

POLICY & REGULATIONS REVIEW

- Department of Housing and Urban Development

In a 1985 document, outdoor day-night sound levels ranging from 65dB to 75dB are described as normally unacceptable for housing and Day-Night average sound level (DNL) from 60dB to 65 dB are described as normally acceptable.

- The Federal Transit Administration

FTA uses DNL to assess noise from mass transit activities. Mass transit includes rapid rail transit or light rail transit, commuter rail, diesel buses, electric buses and trackless trolleys, bus storage yards, rail-transit storage yards, maintenance facilities, stations and subways. It is the FTA criteria for assessing the noise of transit activities below.

These criteria vary with the land use at the location of the noise receiver. The left ordinate is the projected noise exposure for Category 1 and 2 land uses when the proposed transit activity is operating. The right ordinate is the projected noise exposure for Category 3 land uses.

Category 1 - Building or parks where quiet is an essential element of their purpose

Category 2 - Residences and buildings where people normally sleep, include hospitals and hotels where nighttime sensitivity is assumed to be of utmost importance

Category 3 - Institutional land uses with primarily daytime and evening use, such as schools, libraries, churches, and active parks

A-Weighting - This weighting simulates the frequency response of human hearing. The characteristic of this type is that sensitivity decrease in the lower and higher ranges. This weighting is normally used in sound level measurement.

C-Weighting - This weighing is based on relatively flat frequency response and is used for recording AC output of the sound level meter or for measurements of impulsive sound

- The World Health Organization

The World Health Organization (WHO), an agency of the United Nations, recommends a 16-hour daytime average sound level of not more than 55 dB and approximately, and 8-hour nighttime average sound level of not more than 45 dB to prevent serious annoyance in residential areas.

METHODOLOGY

Noise is measured and quantified using a sound level meter and decibels (dB). In the case study, a sound level meter was used and specifications are below

Model DT-8850 IEC 651 TYPE 2 DIGITAL SOUND LEVEL METER

Range Low(35-100dB) and High(65-130dB)

Resolution 0.1 dB

Accuracy 1.5 dB

- Measurement parameter

LAeq, T

This metric is the continuous equivalent sound level. The letter “A” indicates that A-weighting has been used and “eq” indicates that an equivalent level had been calculated. Also “T” denotes measured over time period.

LAMax

This metric is a measure of the peak in sound and is the maximum A-weighting noise level. For train noise, this is the highest level when the train passes in front of receptor location.

- Methods for Noise reductions

в?™ Setbacks: Noise may be reduced by increased the distance between noise sources and receiving use. Setback areas can be open space, roads, recreational areas etc. This technique can reduce generally 4 to 6 dB per doubling of distance from noise sources.

в?™ Barriers: Barriers can mitigate noise by placing walls, berms or other structures such as buildings between noise sources and receivers. Effectiveness of barriers depends on the height of the source, receiver and barriers. In normally, barriers are the most effective when barriers are placed close to noise sources or receivers. Barriers can reduce noise 5 to 15 dB depending on what kind of barriers and what kind of materials.

в?™ Site Design: Buildings can place on the noise areas to shield other residential structures or areas. Also buildings