SU0007300 - Laserfiche WebLink

Home Browse Search

Effects of Single-Event Noise A single event is an individual distinct loud activity, such as an aircraft overflight, train or truck passage. Because most noise policies applicable to transportation noise sources are specified in terms of 24-hour-averaged descriptors, such as Ldn or CNEL, the potential for annoyance or sleep disturbance associated with individual loud events can be masked by the averaging process. Like most jurisdictions, San Joaquin County's noise policies do not address single-event noise. But because this project involves an increase in nighttime truck traffic trips in an area where existing residences are located, single-event noise associated with nighttime truck passages are evaluated in this report. Extensive studies have been conducted regarding the effects of single-event noise on sleep disturbance, with the Sound Exposure Level (SEL) metric being the most common used for such assessments. SEL represents the entire sound energy of a given event normalized into a one-second period regardless of event duration. As a result, the single-number SEL metric contains information pertaining to both event duration and intensity. Another descriptor utilized to assess single-event noise is the maximum, or Lmax, noise level associated with the event. A problem with utilizing Lmax to assess singe events is that the duration of the event is not considered. It should be noted that there is currently an on-going nationwide debate regarding the appropriateness of SEL criteria as a supplement or replacement for cumulative noise level metrics such as Ldn and CNEL, 24-hour noise descriptors. Nonetheless, because SEL describes a receiver's total noise exposure from a single impulsive event, SEL is often used to characterize noise from individual brief loud events. Due to the wide variation in test subjects reactions to noises of various levels (some test subjects were awakened by indoor SEL values of 50 dB, whereas others slept through indoor SEL values exceeding 80 dB), no definitive consensus has been reached with respect to a universal criterion to apply. To the extent that there is any guidance regarding acceptable SEL, the emphasis has been on physiological effects, not on land use planning. The Federal Interagency Committee on Aviation Noise (FICAN) has provided estimates of the percentage of people expected to be awakened when exposed to specific SEL inside a home (FICAN 1997). According to the FICAN study, an estimated 5 to 10% of the population is affected when interior SEL noise levels are between 65 and 81 dB, and few sleep awakenings (less than 5%) are predicted if the interior SEL is less than 65 dB. Environmental Norse Analysis Munn&Perkins Expanded Hours of Operations—San Joaquin County Page 6