SR0082985_SSNL - Laserfiche WebLink

Home Browse Search

4.6 – Noise Draft Environmental Impact Report February 2021 14800 W. Schulte Road Logistics Center 4.6-2 hour average noise level based on the A-weighted sound level. CNEL accounts for the increased noise sensitivity during the evening hours (7 p.m. to 10 p.m.) and nighttime hours (10 p.m. to 7 a.m.) by adding 5 dB to the average sound levels occurring during the evening hours and 10 dB to the sound levels occurring during nighttime hours. Additional noise definitions are provided below. Ambient Noise Level. The composite of noise from all sources near and far. The normal or existing level of environmental noise at a given location. A-Weighted Sound Level (dBA). The sound pressure level in decibels as measured on a sound level meter using the A-weighted filter network. The A-weighting filter deemphasizes the very low and very high frequency components of the sound in a manner similar to the frequency response of the human ear and correlates well with community equivalent sound level. Community Noise Equivalent Level (CNEL). CNEL is the A-weighted equivalent continuous sound exposure level for a 24-hour period with a 5 dB added to the sound during the evening hours (7 p.m.–10 p.m.) and a 10 dB adjustment added to sound levels occurring during the nighttime hours (10 p.m.–7 a.m.). Day Night Average Sound Level (DNL or Ldn). Ldn is similar to the CNEL noise metric, except that no penalty is added during the evening hours (7 p.m.–10 p.m.). Typically, the CNEL and Ldn noise metrics vary by approximately 1 dB or less, and are often considered to be functionally equivalent. Decibel (dB). The decibel is a unit for measuring sound pressure level and is equal to 10 times the logarithm to the base 10 of the ratio of the measured sound pressure squared to a reference pressure, which is 20 micropascals. Vibration Characteristics Vibration is an oscillatory motion through a solid medium in which the motion’s amplitude can be described in terms of displacement, velocity, or acceleration. Vibration can be a serious concern, causing buildings to shake and rumbling sounds to be heard. In contrast to noise, vibration is not a common environmental problem. It is unusual for vibration from sources, such as buses and trucks, to be perceptible, even in locations close to major roads. Some common sources of vibration are trains; buses on rough roads; and construction activities, such as blasting, pile driving, and heavy earth-moving equipment. Several methods are used to quantify vibration. The peak particle velocity (PPV) is defined as the maximum instantaneous peak of the vibration signal. The PPV is most frequently used to describe vibration impacts to buildings, and is usually measured in inches per second. The root mean square amplitude is most frequently used to describe the effect of vibration on the human body and is defined as the average of the squar ed amplitude of the signal. Decibel notation (vibration decibel [VdB]) is commonly used to measure root mean square. The decibel notation acts to compress the range of numbers required to describe vibration. High levels of vibration may cause physical personal injury or damage to buildings. However, vibration levels rarely affect human health. Instead, most people consider vibration to be an annoyance that can affect concentration or disturb sleep. In addition, high levels of vibration can damage fragile buildings or interfere with equipment that is highly sensitive to vibration (e.g., electron microscopes). Most perceptible indoor vibration is caused by sources within buildings, such as operation of mechanical equipment, movement of people, or slamming of doors. Typical outdoor sources of perceptible vibration are construction equipment, steel-wheeled trains, and traffic on rough roads. If the roadway is smooth, the vibration from traffic is rarely perceptible (FTA 2018).