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ANSI/ASA S12.9-2008/Part 6 described a method of predicting the probability of awakening at least once per night due to transportation noise intrusions into residential sleeping quarters. This report summarizes the technical and pragmatic bases for the 2016 decision by ASA Working Group S12/WG 15 to withdraw ANSI/ASA S12.9-2008/Part 6.

ANSI/ASA S12.9-2008/Part 6 was developed primarily to assess sleep disturbance created by transportation noise, as required by NEPA and by similar state legislation, for assessing nighttime noise impacts of major, government-funded projects. Limitations of the Standard (described in clause 2 below) that have become evident in the years since its publication outweigh its usefulness for its intended purpose.

The decision of Working Group S12/WG 15 to withdraw ANSI/ASA S12.9-2008/Part 6 implies that the method for calculating "at least one behavioral awakening per night" contained in the former Standard should no longer be relied upon for environmental impact assessment purposes. The Working Group believes that continued reliance on the 2008 Standard would lead to unreliable and difficult-to-interpret predictions of transportation-noise-induced sleep disturbance.

The Working Group further believes that project alternatives that have been endorsed in alreadycompleted environmental assessments on the basis of calculations of "at least one behavioral awakening per night" may be in error and have overestimated numbers of expected awakenings. The Working Group understands that its decision to withdraw the 2008 Standard may be disruptive to acoustical consultants who rely on the Standard for environmental impact assessment purposes. Therefore, two Informative Annexes of the 2008 standard are included in this document for the guidance they can provide until more plausible and technically defensible means are developed for predicting sleep disturbance due to transportation noise.¹

¹ Practitioners and the public may benefit from information that describes the difference between awakening in habituated and unhabituated populations. Higher noise levels have been reported to be required to disturb sleep in an habituated population than for a non-habituated population [Ollerhead, 1992]. This finding may be relevant in assessments conducted for NEPA-related purposes of project-related noise effects on sleep disturbance.