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Rochat is Principal Asso-ciate, ATS Consulting,Los Angeles, California,and Chair of the TRBTransportation-RelatedNoise and VibrationCommittee. Zevitas isSenior EnvironmentalEngineer, and Rapoza isAcoustical Engineer,Volpe National Trans-portation Systems Center,Research and InnovativeTechnology Administra-tion, U.S. Department ofTransportation, Cam-bridge, Massachusetts.

In comparison with the built environment, parksand other natural settings offer a measurable dif-ference in air quality, sounds, and open spaces.

Research has shown that time spent in natural set-tings can improve a person’s mood and sense of well-being, can increase cognitive performance and sleepquality, and can attenuate stress or response to pain.Park visitors and wildlife, however, can suffer fromthe adverse effects of noise from on- and off-roadvehicles, as well as from military and commercialaircraft, including air tours over parks.

The National Park Service, the Federal AviationAdministration, and other organizations have beenworking to understand and reduce these transporta-tion noise sources to protect the sound environmentsin parks. Recent work includes the following:

u Conducting research to help parks assess, pre-dict, and minimize road noise;

u Evaluating the impact of aviation noise on apark visitor’s experience; and

u Outlining a comprehensive program to evalu-ate the potential health benefits of the natural soundspotentially masked by road noise and aviation noise.

More information on each topic is availablethrough the Natural Sounds and Night Skies Divisionof the National Park Service1 and the U.S. Depart-ment of Transportation’s Volpe Center.2

Motorcycles and PavementsTo help parks assess, predict, and minimize roadnoise in the park environment, research has focusedon motorcycle noise and on quieter pavements.Motorcycle noise was measured on the side of theroad and in noise-sensitive locations at Blue RidgeParkway National Park. Motorcycles were classifiedinto five categories for inclusion in a special researchversion of the Federal Highway Administration’sTraffic Noise Model (TNM). The model has helpedin examining and understanding motorcycle noiseand its effects and has contributed to informed deci-sion making about ways to reduce motorcycle noisein a park setting.

Two documents were written to guide the use ofquieter pavement types and quieter, bicycle-friendly

Noise and Natural Sounds in America’sNational ParksJ U D I T H L . R O C H A T , C H R I S T O P H E R D . Z E V I T A S , A N D A M A N D A S . R A P O Z A

Environmental Sustainability in Transportation

Motorcycle traffic was studied as a potential sourceof controllable noise in national parks.

(Photo above:) Aircraftoverflight, Zion NationalPark.

1www.nature.nps.gov/sound_night/.2www.volpe.dot.gov/coi/ees/index.html.

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rumble strips. Another research version of TNM wasgenerated for quieter pavements and included thenoise effects of various pavement types. Tire–pave-ment and sensitive receiver–location noise mea-surements were conducted at Death Valley NationalPark; the measured sound levels were used with themodel to demonstrate the potential effectiveness ofquieter pavement in a park environment. This typeof analysis can be applied to any park to determinepotential noise reductions and to help in makingroadway paving decisions that benefit the acousticenvironment.

Judging Aviation NoiseThe potential impact of aviation noise on a park vis-itor’s experience will likely be assessed with bothquantitative and qualitative criteria. Qualitative vis-itor responses can be related to quantitative noiseexposure through mathematical expressions devel-oped to describe the relationship between the noiseexposure during a park visit and the visitor’s judg-ment about the impact of the exposure on the qual-ity of the experience, as stated in an on-site survey.

To develop these criteria, experts in the social sci-ences, natural resource management, and acousticscollaborated on the research strategies, data collec-tion methods, and survey instruments. During thesummer of 2011, more than 4,500 visitor surveysand corresponding measurements of the soundscapeand aircraft noise were collected at seven backcoun-try locations in four national parks. In conjunctionwith similar data collected in the 1990s, the resultswere used to examine the correlation between noiseexposure and subjective visitor responses.

Dose–response relationships were developed thatshowed the following:

u Noise exposure, described in terms of theequivalent sound level from aircraft during the visit,

correlated well with visitor response.u The visit context strongly influenced the

response—visitor activity, opinion on the importanceof natural quiet, time spent at the site, familiaritywith the site, and the presence of children in thegroup were important factors.

u The types of aircraft generating the noise expo-sure dose were important—visitors reacted morenegatively to helicopters than to fixed-wing aircraft,propeller planes, and high-altitude jets.

Benefits of Natural SoundsTo determine the potential benefit of natural sounds,a research approach must characterize the underly-ing value of the acoustical environment. This can bedone through a comprehensive program based oninvestigation of objective, physiological outcomes,such as cognitive performance, attention, anxiety,fatigue, heart rate, blood pressure, increased pro-ductivity, and more. The aim of the program wouldbe to

u Identify the physiological and behavioralresponses associated with exposure to naturalsounds, such as sounds of the ocean, the forest, andthe desert;

u Evaluate the therapeutic potential of exposureto natural sounds for vulnerable populations such asveterans with posttraumatic stress or children withattention-deficit hyperactivity disorder; and

u Build a comprehensive base of evidence to sup-port public policy decisions directly related to themanagement of soundscapes in national parks andindirectly related to health care services, air trafficmanagement, and urban planning, among otherthings.

The target research population would be thosewho could benefit, including children, backpackers,veterans, and workers exposed to natural sounds.

Vehicle equipped for research on tire–pavementnoise on a roadway in Death Valley National Park.

National park visitorscomplete a survey on theimpact of aviation noiseon their park experience.

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