01054354

Component

Noise modeling is a vital part of designing any facility with fixed noise sources in order to meet community noise limits, and ISO 9613-2 is the most commonly used methodology in models to predict outdoors propagation. Although many types of noise limits are encountered for facilities – industrial, commercial, or institutional, an A-weighted not-to-exceed limit is the most common. As atmospheric conditions substantially affect actual levels, the relationship between atmospheric conditions and predicted noise levels needs to be understood. ISO 9613-2 (hereafter 9613) predicts, at least it is intended to predict, a long-term average downwind level during conditions favorable to propagation, including mild inversions. The accuracy and adequacy of the methodology in 9613 have long been questioned. Recent measurements by Schomer2 suggest that 9613 predicts for average crosswind rather average downwind conditions. Because 9613 predicts a long-term downwind average, actual levels will – by the definition of average – sometimes, and possibly frequently, exceed the predicted average level. The percentage of the time the predicted level will be exceeded, and by how much, is not known. A not-to-exceed limit may need to be met under near-worst case atmospheric conditions that are more severe and occur less frequently than the average conditions of 9613. ISO 9613-2 is probably the most widely used international standard, and has been used successfully for designing a great many facilities to meet noise limits. There seems to be a dichotomy between successful results and known deficiencies in 9613. In general, 9613 works for many conditions, and does not work as well for others. This paper summarizes deficiencies in 9613 and then attempts to answer the following questions: (1) What is predicted by 9613? (2) When does 9613 give reasonably accurate results, and when are they less accurate? (3) Does 9613 predict what it claims to predict? (4) Is a 9613 average suitable for designing to meet a not-to-exceed limit? When and how 9613 can be used successfully? Another question is raised but cannot be answered, namely, how often can a not-to-exceed limit be exceeded and still be acceptable for design purposes. Design strategies are also suggested.

01054353

English

pp 861-873

2004

Noise-Con 04. The 2004 National Conference on Noise Control Engineering

CD-ROM

Figures (5) ; References (36) ; Tables (1)

Communities; Design; Noise; Noise control; Noise sources; Outdoor recreation; Sound level meters; Sound transmission

Outdoor

Design; Energy; Environment; Highways; I15: Environment

TRIS, TRB

Jul 26 2007 1:25PM