The National Park Service (NPS) administers the National Park System for both recreational use and preservation of park resources, a mission that can be contradictory. Increased recreation on NPS lands has fueled disagreements over this dual mission and over the optimum extent of motorized versus nonmotorized recreational activities. The National Park System, with 401 units covering approximately 85 million acres of land, received more than 268 million recreational visits in 2013. Use of off-highway vehicles (OHVs) in the parks—including all-terrain vehicles (ATVs), snowmobiles, personal watercraft, and others—along with recreational activities such as mountain biking, snow biking, heli-skiing, and aircraft tours, have evolved and gained in popularity. These newer forms intersect with more traditional, nonmotorized forms of recreation, including land-based activities such as hiking, camping, hunting, birdwatching, horseback riding, and rock climbing, and water-based pursuits such as fishing, canoeing, kayaking, and rafting. OHV use in the parks has been particularly contentious, although NPS has fewer lands open to OHVs than do other federal land management agencies such as the Bureau of Land Management (BLM) and the Forest Service (FS). OHV supporters contend that the vehicles allow visitors access to hard-to-reach natural areas; bring economic benefits to communities serving riders; provide outdoor recreation opportunities for the disabled, senior citizens, and others with mobility limitations; and, in the case of snowmobiles, allow increased access to sites during winter. They assert that technological advances will continue to limit noise and pollution. By contrast, opponents of OHVs in the National Park System assert that these vehicles damage the environment and cultural artifacts, pose safety concerns, and conflict with other forms of recreation. NPS staffing levels, they contend, are inadequate to effectively monitor motorized use and its impact on park resources. Opponents also cite the availability of other federal lands, such as BLM and FS lands, where OHV use may be permitted. Among environmental concerns raised by OHV critics are potential damage to wildlife habitat and land and water ecosystems; the impact of dust on winter snow melts and water supply; noise, air, and water pollution; and a diminished experience for recreationists seeking quiet and solitude and/or hunting and fishing opportunities. Critics also point to the beneficial economic impact of nonmotorized recreation on local communities. The 113 th Congress has addressed motorized recreation in the National Park System through legislation and oversight. Bills concerning motorized recreation at NPS units include H.R. 819 , H.R. 2954 , and S. 486 , all of which would change regulations for OHVs at Cape Hatteras National Seashore; and H.R. 3590 , as amended ( H.Amdt. 538 ), which would prohibit NPS from altering regulations that allow the use of motorized vessels for fishing at Ozark National Scenic Riverways. In its oversight role, the House Natural Resources Committee has held hearings on outdoor recreation, including motorized and nonmotorized uses, on federal lands. A May 2013 hearing addressed outdoor recreation issues such as insurance and permitting problems for outfitters and guides. A June 2013 hearing discussed federal, state, and local interactions regarding outdoor recreation and addressed problems of coordination, trail and travel planning, conflicts between motorized and nonmotorized uses, and local input into agency planning. Two executive orders define and generally guide OHV use on federal lands. The first (E.O. 11644, February 8, 1972) defines an off-road vehicle, now commonly referred to as an off-highway vehicle, as "any motorized vehicle designed for or capable of cross country travel on or immediately over land, water, sand, snow, ice, marsh, swampland, or other natural terrain," with exceptions for any registered motorboat or authorized or emergency vehicles. It was issued to "establish policies and provide for procedures that will ensure that the use of off-road vehicles on public lands will be controlled and directed so as to protect the resources of those lands, to promote the safety of all users of those lands, and to minimize conflicts among the various uses of those lands." The order directed each agency to develop and issue regulations to carry out this purpose and to provide for the designation of areas and trails on which OHVs may be permitted, and areas in which such vehicles would not be permitted. Agencies were to monitor the effects of OHV use and amend or rescind area designations or other actions taken pursuant to the order as needed to further the policy of the executive order. A subsequent executive order (E.O. 11989, May 24, 1977) amended the 1972 order to exclude military, emergency, and law enforcement vehicles from the definition of off-road vehicles (to which restrictions would apply). It provided authority to immediately close areas or trails if OHVs were causing or would cause considerable damage to the soil, vegetation, wildlife, wildlife habitat, or cultural or historic resources of particular areas or trails. Areas could remain closed until the manager determined that "the adverse effects have been eliminated and that measures have been implemented to prevent future recurrence." Also, each agency was authorized to adopt the policy that areas could be closed to OHV use except for those areas or trails that are specifically designated as open to such use. This meant that only open areas would have to be marked, a lesser burden on the agencies. While the executive orders apply to federal lands generally, other authorities concerning OHVs are specific to the National Park System. In particular, NPS regulations generally limit OHV use in the park system to four types of NPS units—national recreation areas, national seashores, national lakeshores, and national preserves. The regulations also require special rulemaking, with environmental impact analysis and public comment, to designate routes and areas for OHVs in these park units. NPS's management policies provide additional guidance, stating that OHV use "may be allowed only in locations where there will be no adverse impacts on the area's natural, cultural, scenic, and esthetic values, and in consideration of other existing or proposed recreational uses." In general, the management policies emphasize the conservation of park resources in conservation/use conflicts. Although the executive orders cited earlier include oversnow vehicles in the definition of OHVs, the NPS regulations that permit OHV use only at certain types of park units do not apply to snowmobiles. Instead, snowmobile use in the National Park System is governed by separate regulations that limit such vehicles to designated routes and water surfaces that are used by motor vehicles or motorboats during other seasons. The regulations prohibit snowmobiles except "when their use is consistent with the park's natural, cultural, scenic and aesthetic values, safety considerations, [and] park management objectives, and will not disturb wildlife or damage park resources." NPS management policies further state that snowmobile use can be authorized only where it will not result in unacceptable impacts. The enabling legislation for individual NPS units may establish specific activities as an appropriate use (e.g., water-oriented recreation, snowmobiling for subsistence or recreational purposes, or OHV travel to reach hunting or fishing areas). Additional unit-level direction for designated routes (such as temporary route closures) may be included in a park's general management plan and/or determined by the park superintendent. Excluding Alaska, 13 NPS units allow off-road use of ATVs, four-wheel drive vehicles, and/or dune, sand, and swamp buggies by the general public. Environmental groups have alleged that these vehicles damage wildlife habitat and disturb nonmotorized activities, both in the units that permit their use and in other areas where, they claim, unauthorized use occurs. Users of the vehicles, by contrast, have sought more routes and areas for off-road recreation and increased motorized access to hunting and fishing sites. They assert that NPS restrictions harm communities surrounding parks, which depend on business generated by OHV users. NPS is in the process of issuing special regulations to designate routes and areas for off-road use in those units that permit ATVs and oversand vehicles. Eleven of the 13 park units have special regulations in place: Big Cypress National Preserve; Apostle Islands National Lakeshore; Curecanti, Gateway, and Lake Meredith National Recreation Areas (NRAs); and Assateague, Cape Cod, Cape Hatteras, Fire Island, Gulf Islands, and Padre Island National Seashores. Two additional units are open to public use while NPS completes OHV management planning: Glen Canyon NRA and Cape Lookout National Seashore. Also, Lake Meredith and Curecanti NRAs and Big Cypress National Preserve are developing regulations to change the current boundaries for OHV riders. Other areas that once allowed public off-road use of ATVs and oversand vehicles are now closed to such use, including Little River Canyon National Preserve and Big South Fork National River and Recreation Area. Some of NPS's regulatory actions respond to a 2005 lawsuit by environmental organizations. The groups alleged that ATVs and other off-highway vehicles constituted a "serious threat" to NPS resources that the agency failed to address. The parties settled in 2008. NPS is still addressing some requirements of the settlement, such as the requirement that the agency develop environmental impact statements and special rules governing OHV use at Glen Canyon NRA and Cape Lookout National Seashore. (Cape Lookout has completed public scoping and is developing a draft alternative OHV management plan and environmental assessment; Glen Canyon released a draft plan in January 2014.) Also in response to the settlement agreement, NPS is encouraging education via the websites of units permitting OHV use.