In managing its lands, the National Park Service (NPS) seeks to balance a dual statutory mission of preserving natural resources while providing for their enjoyment by the public. Motorized recreation on NPS lands sometimes brings the two parts of this mission into conflict. Offhighway vehicles (OHVs) have been particularly controversial, with calls for greater recreational access intersecting with concerns about environmental impacts and disturbance of quieter pursuits. NPS’s laws, regulations, and policies generally emphasize the conservation of park resources in conservation/use conflicts, and NPS has fewer lands open to OHV use than do other federal land management agencies such as the Bureau of Land Management and the Forest Service. The 113th Congress may address motorized recreation in the National Park System, either through broad measures (such as those concerning recreational access to federal lands) or through specific measures affecting motorized recreation at particular NPS units.ATVs and Oversand Vehicles. Only 12 of the 398 park units are open to public recreational use of all-terrain vehicles (ATVs), four-wheel drive vehicles, and/or dune, sand, and swamp buggies. The extent of unauthorized use of such vehicles is in dispute. Several units are developing pilot education and deterrence programs to address unauthorized use. Legislative measures in the 112th Congress sought to regulate OHV use at one NPS site, Cape Hatteras National Seashore.Snowmobiles. Regulatory and judicial actions to allow or restrict snowmobile use have focused primarily on three Yellowstone-area park units. Winter use plans developed by NPS to establish numerical limits on snowmobile and snowcoach entries have been the subject of repeated, and often conflicting, court challenges. Most recently, NPS has issued a draft plan and supplemental environmental impact statement intended to govern snowmobile use at Yellowstone for the 2014- 2015 winter season and beyond. The plan would allow up to 110 “transportation events” per day (defined as the use of either a multipassenger snowcoach or a group of snowmobiles).Aircraft Overflights. Grand Canyon National Park is at the center of a conflict over whether or how to limit air tours over national park units to reduce noise. NPS and the Federal Aviation Administration (FAA) continue to work to implement a 1987 law (P.L. 100-91) that sought to reduce noise at Grand Canyon, and a 2000 law (P.L. 106-181) that regulates overflights at other park units. P.L. 112-141, enacted in 2012, contains provisions on air tour management at Grand Canyon, including some less-stringent standards for natural quiet than NPS had recommended in planning efforts. P.L. 112-95 contains provisions to expedite and streamline agency planning actions for commercial air tours over parks generally.Personal Watercraft (PWC). Since 2003, NPS has completed regulations to open designated PWC areas at 13 units. In July 2010, a federal judge ordered NPS to re-examine environmental assessments justifying PWC use at two of those units but did not overturn existing regulations.Mountain Bicycles. This mechanized though nonmotorized activity also raises issues of the sufficiency of access to park lands as well as potential resource damage and disturbance of quieter recreational pursuits. Currently, more than 40 NPS units allow mountain biking on dirt trails and/or dirt roads. Mountain biking advocates have worked with NPS to explore opportunities to increase this activity in park units. In July 2012, NPS finalized a rule that eases the process for park superintendents to open trails to bicycles.