How much noise is too much?

People complete a noise survey near the entrance to Denali National Park. NPS/Lauren Ferguson

National Park Service Natural Sounds and Night Skies Division staff and partners at the University of New Hampshire, The Pennsylvania State University, Stanford University, and the Norwegian Institute for Nature Research recently published research in the journal Applied Acoustics. The paper analyzes visitor experience in the entrance area of Denali National Park and Preserve. The purpose of this study was to survey, model, and map visitor response to aircraft noise with a focus on takeoffs from the McKinley National Park Airport. Results suggest an entrance area management threshold for noise at LAeq,30s = 54 dB. This aligns with federal guidance that identified 55 dB as a threshold for interference with outdoor activities at rural residences and schools. The results also include a spatial map of visitor response. Managers can use these results and methods to manage transportation capacity as well as visitor use throughout the entrance area.

Highlights

• Surveys were used to measure the effects of air tour noise on visitor experience.
• Visitors rated the acceptability of 5 randomly chosen recordings of aircraft noise.
• Modeling was used to predict decreases of acceptability with increasing noise.
• Negative effects of noise were moderated for visitors who had interest in air tours.
• Maps of predicted visitor acceptability of air tour noise were produced.

Also see:

Denali National Park Frontcountry Sounds: Impacts of Noise on Visitors' Experience

Overview of method for developing spatial maps representing visitor response to aircraft noise. NPS/published in Applied Acoustics

How much noise is too much? Methods for identifying thresholds for soundscape quality and ecosystem services

Abstract

The United States National Park Service mandate is to conserve park resources and provide superlative visitor experience. In the context of acoustic resources, Denali National Park and Preserve provides an advantageous opportunity to understand the effect of aircraft noise on visitor experience because it possesses high levels of air tour traffic in a park renowned for its remote, wilderness character. Park visitors in four different settings were asked to rate the acceptability of recordings of aircraft noise, presented in randomized order relative to noise level. A cumulative link mixed model fitted visitor assessments to acoustic and nonacoustic factors. In addition to noise level, interest in an air tour was an important predictor of sound clip acceptability. For visitors uninterested in an air tour, the probability of rating aircraft noise as unacceptable at 54 dB LAeq,30 s or higher was 26%. For reference, this aligns with federal guidance that identified 55 dB as a threshold for interference with outdoor activities at rural residences and schools. Predictions of visitor response were joined to a spatial model of aircraft noise propagation to map visitor acceptability of aircraft noise in Denali’s entrance area (frontcountry). This map can be used to assess the condition of park management zones, to inform hiking recommendations for visitors, and to predict the range of soundscape conditions experienced by park visitors.

Ferguson, L. A., P. Newman, M. F. McKenna, D. H. Betchkal, Z. D. Miller, R. Keller, K. M. Fristrup, and B. D. Taff. 2023. How much noise is too much? Methods for identifying thresholds for soundscape quality and ecosystem services. Applied Acoustics 209: 109388.

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