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Noise Sources


Cars and other motorized vehicles are one of the most dominant and pervasive sources of noise in national parks. A 1997 Memorandum of Understanding between the Secretary of Transportation and the Secretary of the Interior noted that "Congestion in many National Parks is causing lengthy traffic delays and backups that substantially detract from the visitor experience. Visitors find that many of the National Parks contain significant levels of sound and air pollution and traffic congestion similar to that found on the city streets they left behind."

In many National Park units, the existing infrastructure and transportation systems are at or beyond the capacity for which they were designed during high visitation periods. Consequently, parks have started addressing vehicle congestion and noise by offering alternatives to driving single family vehicles. In conjunction with these measures, the Natural Sounds Program is working with parks to educate their user groups on the importance of respectful and responsible use.

Traffic Jam
"Eighty-three percent of the land area of the continental US is within 1061 meters of a road [Barber, Crooks, & Fristrup, 2009, p. 182]." NPS photo.

At Zion National Park between 1982 and 1997, as many as 5,000 cars a day were lining up on holiday weekends to enter the canyon. Park managers established a shuttle system through the most popular portions of the park in order to mitigate the congestion and noise during peak visitation times. Though the change was initially controversial, today park staff members report an overwhelmingly positive public response. Visitors frequently comment that the park is much more serene without the presence of cars. Wildlife health and behavior were also affected by the restored tranquility. In the years preceding the decision, several animal species had moved far from the main roads to avoid vehicular sounds. Today visitors report seeing increasing numbers of wildlife in the valley.

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For some visitors few experiences can compare to the dizzying sensation of soaring over dramatic hanging valleys or of being dwarfed by the looming walls of Mount McKinley as seen from the windows of a tiny aircraft. The popularity of such activities is evidenced in the increasing numbers of recreational overflights in national parks. In Grand Canyon alone, the number of tour overflights grew by 37% between 1987 and 2005 (Bell, Mace, & Benfield, 2009). These figures do not include the vast numbers of commercial and general aviation flights occurring over Grand Canyon. In fact, all forms of aviation activities over parks, including commercial passenger flights, park maintenance, scientific research, and fire and emergency operations, have increased in recent years. The impact of such activities to the rafter drifting through the silent backcountry or the pika listening for warning calls, for example, is one question park managers must grapple with when drafting management plans. In an effort to address the growing problem of air tour noise over units of the National Park System, Congress mandated the Federal Aviation Administration (FAA) and the National Park Service to work together to mitigate or prevent adverse impacts to park resources and values from commercial air tours. The resulting National Parks Air Tour Management Act of 2000 requires the cooperative development of commercial Air Tour Management Plans (ATMPs) for each of the over 106 parks where such tours operate. As of 2011, ATMPs are being developed for multiple parks including Hawaii Volcanoes, Haleakala, Mount Rushmore, Badlands, Mount Rainier, Death Valley, Big Cypress, Petrified Forest, and the Statue of Liberty. For more information on ATMPs, please visit our Useful Resources page.

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Snowmobiles and Off-Highway Vehicles

Before their numbers were limited, one could count as many as 1,500 snowmobiles a day in Yellowstone National Park. In a 2000 National Parks Conservation Association study, the machines could be heard 90 percent of the time at eight popular sites (National Park Conservation Association & Greater Yellowstone Coalition Yellowstone, 2000). In addition to the pervasive noise, are concerns about impacts on wildlife, air and water quality, and the threat to one of the park's most alluring values—its wildness.

The issue extends far beyond the boundaries of Yellowstone and the clamor of the snowmobile. Public lands throughout the country are feeling the pressure of increasing numbers and types of off-highway vehicles (OHVs). Public opinion on both sides of the argument is vehement. While many view mounting regulations as infringing on the right to enjoy their public lands, others see a problem that is already out of control.

Snowmobiles at Yellowstone National Park
Yellowstone National Park is using acoustical data to help create winter use policies that protect the resource while allowing for a variety of winter activities. NPS photo.

After years of public debate and research, Yellowstone has set some limits on snowmobiles. While awaiting the conclusion of the Winter Use Plan/Environmental Impact Statement, the park has restricted snowmobile use to 318 a day. All must be led by commercial guides and use new cleaner and quieter machines. According to Al Nash, Yellowstone National Park's Chief of Public Affairs, "the shift from historical unmanaged winter use to limited and managed use, and sounds and emissions requirements has resulted in quieter conditions in Yellowstone in winter." In fact, in the years following the new regulations, Yellowstone staff has measured some of the quietest conditions they have ever recorded in the natural environment.

Acoustical data may also play a role in creating policies regarding ORVs in national parks. Using noise mapping models, the Natural Sounds Program is helping Big Cypress National Preserve, Cape Hatteras National Seashore, and Grand Canyon-Parashant National Monument to better understand and manage ORV use. By superimposing the noise footprint and intensity of selected activities over area maps, these models reveal significant and sometimes startling information about how and where noise travels.

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Park Operations

Snow Plow
Snow plows are used in some parks to allow visitation in winter months. NPS photo.

Park operations, including construction, mowing, and aircraft use, as well as park infrastructure, such as heating and ventilation units, can also have impacts on park acoustical environments. NPS Management policies, however, direct superintendents to "monitor mechanical noise that adversely affects opportunities to enjoy park soundscapes." Consequently, while sounds from such operations are inevitable, parks are working to find "quieter" ways of performing necessary tasks. Such measures might include scheduling noisy activities around noise-sensitive times of day (i.e., when interpretive programs are conducted, sensitive times for wildlife), using quieter tools when feasible, and locating noisy equipment as far from sensitive areas as possible.

Denali National Park and Preserve has been an early and exemplary leader in soundscape management. Though the park contains some of the most remote places in the national park system, there was a time when a visit to the Wonder Lake Ranger Station was less than peaceful. A noisy 30-kilowatt diesel generator that powered the station ran 24 hours a day. As part of its planning process, park personnel set out to mitigate the generator noise by installing a bank of batteries that greatly limited its run time. The result was a quieter acoustical environment and a restored sense of the solitude that is Denali's heritage.

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The National Park Service has determined that personal watercraft (PWC) use can "have a direct and adverse effect on park values such as peace and quiet." In April 2000, PWC use was banned in national park areas unless it is consistent with the unit's enabling legislation or overall management objectives. As with snowmobiles, OHVs, and other forms of motorized recreation, measuring the noise levels of PWCs has helped park managers assess and evaluate impacts in order to make more informed decisions.

Today the Natural Sounds Program provides valuable data and guidance for this on-going issue. After collecting noise source measurements of airboats and motorboats in Everglades National Park, the Natural Sounds Program modeled their potential noise impacts. The results from such modeling will help to inform future park planning efforts. Similar efforts are underway throughout the National Park System.

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Military Overflights

Plane flying over Alcatraz Island
Airplane flying over Alcatraz Island. NPS photo.

Various efforts between the National Park Service and the U.S. Air Force (USAF) have resulted in greater mutual cooperation over the past decade. Attendance by both parties at Airspace and Range Council meetings, for example, and NPS-sponsored backcountry trips for military officers and park managers have helped build relationships and resulted in more collaborative problem solving. Heralded as an outstanding example of a cooperative relationship between the NPS and USAF, the jointly developed military sourcebook helps both agencies better address military overflights in the Pacific Northwest National Parks. Versions covering other regions are planned.

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Airports and Development

A visitor pauses reflectively at the site of the opening battle of the American Revolution, in Minute Man National Historical Park. Her mind naturally conjures the crack of a rifle, and the sounds of chaos that mark a defining moment in the nation's history. Through her mental window she begins to imagine herself as a young mother, desperate to gather her children, when the puttering of a small commuter plane jolts her back to the present. Another zooms by, destined for the adjacent airfield. Her reverie disintegrates.

This scenario could play out for thousands of park visitors as Americans increasingly rely on small, regional airports. As demand for their services increase, these facilities seek to enhance their capacity to handle more traffic and as a result, the interface between national parks and urban areas has increased substantially.  A host of other sites, including Death Valley, Yosemite, and Grand Teton, face potential noise impacts from regional airport expansion. Careful examination of soundscapes should be addressed at all levels of planning to ensure the implementation of thoughtful and sustainable solutions for protecting park soundscapes.

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Energy Development

While the roar of a waterfall or an elk's bugle can be stirring experiences, the earth often speaks in whispers. John Muir once wrote, "The faint lisp of snowflakes as they alight is one of the smallest sounds a mortal can hear. The sound of falling sequoia seeds, even when they happen to strike on flat leaves or flakes of bark, is about as faint." The sound of silence offers tremendous opportunities to discover earth's secrets.

Great Sand Dunes National Park and Preserve
Visitors to Great Sand Dunes National Park and Preserve can enjoy some of the most profound silence yet discovered by the Natural Sounds Program's acoustical monitoring team. NPS Photo.

Great Sand Dunes National Park and Preserve enjoys some of the most profound silence yet discovered by the Natural Sounds Program's acoustical monitoring team. Yet this silence, as with national park soundscapes nationwide, has become vulnerable to the burgeoning demand for energy development. While Great Sand Dunes is confronted with potential oil and gas drilling near its border, impacts to national park soundscapes come from all types of energy development, including geothermal, hydropower, wind, and even solar. Loss of natural quiet, however, transcends the human experience. Wildlife habitat, reproduction, and migration routes are at jeopardy as well, as the noise from such development encroaches on wild areas.

Sustainable energy development and infrastructure is both necessary and important; as is the mitigation of impacts it creates. Given the potential consequences of such development, the value of reliable acoustical data cannot be overstated. The Natural Sounds Program has begun developing new protocols for assessing impacts from nearby industrial noise sources. Close coordination between park management, cooperating agencies, and commercial interests will be required in order to ensure that energy development projects are compatible with the protection of park resources and visitor enjoyment.

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Bell, P. A., Mace, B. L., & Benfield, J. A. (2009). Aircraft overflights at national parks: Conflict and its potential resolution. Park Science, 26(3), 65-67.

Last Updated: April 17, 2012