T he National Trails System Act (16 U.S.C. §§1241-1251) of 1968 established the Appalachian and Pacific Crest National Scenic Trails, and authorized a national system of trails to provide outdoor recreational opportunities and to promote access to the nation's outdoor areas and historic resources. Since the act's passage, the system has grown to encompass trails in every U.S. state, Washington, DC, and Puerto Rico. The system has expanded over time and now includes four types of trails: National Scenic Trails (NSTs) display significant characteristics of the nation's "physiographic regions," representing desert, marsh, grassland, mountain, canyon, river, forest, or other areas. NSTs provide for outdoor recreation and for the conservation and enjoyment of significant scenic, historic, natural, or cultural qualities. National Historic Trails (NHTs) identify and protect travel routes of national historic significance, along with associated remnants and artifacts, for public use and enjoyment. NHTs can include land or water segments, marked highways paralleling the route, and sites that together form a chain or network along the historic route. National Recreation Trails (NRTs) are on federal, state, or private lands that are in, or reasonably accessible to, urban areas. They provide for a variety of outdoor recreation uses. Connecting or Side Trails provide public access to the other types of nationally designated trails or connections between such trails. Congress plays an ongoing role in shaping the National Trails System through legislation and oversight. Congress establishes new trails within the system; directs the Administration to study potential new trails; determines the level of agency funding for trail management; and considers whether new trail categories (such as "national discovery trails") should be included in the system, among other roles. For individual trails, Congress has made specific provisions concerning land acquisition, trail use, and other matters. Ongoing issues for Congress include whether to designate additional trails, how to balance trail designation with other potential land uses, whether trail designation should be accompanied by federal land acquisition, what activities should be permitted on trails, and how to appropriately balance federal and nonfederal funding for trails, among other issues. During the early history of the United States, trails served as routes for commerce and migration. Since at least the early 20 th century, trails also have been constructed to provide access to scenic areas. The first interstate recreational trail, now known as the Appalachian National Scenic Trail, was developed in the 1920s and 1930s. In 1945, legislation to establish a "national system of foot trails" was introduced but not reported. In the years following the Second World War, the nation sought better opportunities to enjoy the outdoors. In 1965, in a message to Congress on "Natural Beauty," President Lyndon Johnson called for the nation "to copy the great Appalachian Trail in all parts of our country, and make full use of rights-of-way and other public paths." Three years later, the National Trails System Act was enacted. The system began in 1968 with two scenic trails: the Appalachian National Scenic Trail, which stretches roughly 2,180 miles from Mount Katahdin, ME, to Springer Mountain, GA; and the Pacific Crest National Scenic Trail, which covers roughly 2,650 miles along the mountains of Washington, Oregon, and California. The system was expanded a decade later when Congress designated four historic trails, with more than 9,000 miles, and another scenic trail, along the Continental Divide, with 3,100 miles. Currently, there are a combined 30 NHTs and NSTs covering almost 55,000 miles. (See Table 1 and Figure 1 .) Additionally, the system contains more than 1,200 NRTs and 6 connecting or side trails, including trails in every state, Washington, DC, and Puerto Rico. The National Trails System Act also authorizes the preservation of abandoned railroad rights-of-way for rails-to-trails conversions (16 U.S.C. §1247). NSTs and NHTs are designated by acts of Congress. Prior to establishing a trail, Congress typically directs the Secretary of the Interior or the Secretary of Agriculture to study the route for potential inclusion in the system. The studies address both the suitability (i.e., characteristics that make the proposed trail "worthy of designation as a national scenic or national historic trail") and the feasibility (i.e., physical and financial viability) of adding the trail to the system. The act contains additional criteria for NHTs, which must (1) be established by historic use and be significant because of that use; (2) be significant with respect to a broad facet of American history, such as trade and commerce, exploration, migration and settlement, or military campaigns; and (3) have significant potential for public recreational use or historical interest. In contrast to national scenic and historic trails, national recreation trails may be designated by the Secretaries of the Interior and Agriculture with the consent of the federal agency, state, or political subdivision with jurisdiction over the lands involved. Recreation trails must be reasonably accessible to urban areas and must meet other criteria as prescribed by the act or by the Secretaries. The Secretaries also have authority to designate connecting and side trails. For all four trail types, routes may intersect both federal and nonfederal lands. The law provides limited authorities for federal land acquisition in connection with the trails. Along the designated rights-of-way for NSTs and NHTs, the Secretaries may acquire land in areas that are already under their administrative jurisdiction (e.g., on trail segments that lie within the boundaries of an existing national park or national forest but are not federally owned). Outside their administrative boundaries, the Secretaries are to encourage state and local governments either to acquire trail lands or to enter into agreements with private landowners for the necessary rights-of-way. Only if state and local governments fail to do so may the federal government acquire the land or form cooperative agreements with landowners. For NRTs, the provisions are more limited, in that federal land acquisition may take place only within existing administrative boundaries. Connecting and side trails may only include nonfederal lands if no federal acquisition is involved. When adding individual trails to the system, Congress has often included specific land acquisition provisions—for example, authorizing federal acquisition only from willing sellers or establishing a geographical boundary for land acquisition, such as within a quarter-mile on either side of the trail. P.L. 111-11 gave federal land management agencies the authority to purchase land from willing sellers for a number of trails that had previously prohibited any federal land acquisition. The 30 national scenic and historic trails are administered by either the Secretary of the Interior or the Secretary of Agriculture, acting through the land management agencies. The NPS administers 21 of the 30 trails; the FS administers 6 trails; the Bureau of Land Management (BLM) administers 1 trail; and the NPS and BLM jointly administer 2 trails. The administering agency typically develops the trail management plan, oversees development of trail segments, coordinates trail marking and mapping, develops maintenance standards, coordinates trail interpretation, administers cooperative and interagency agreements, and provides financial assistance to others for trail purposes, among other functions. The agencies point to a distinction between trail administration and trail management : while there is usually only one administering agency, multiple federal agencies, state and local governments, private groups, and individuals may own and manage lands along a national scenic or historic trail. The National Trails System Act authorizes the administering Secretary to enter into cooperative agreements with state, local, and private landowners or organizations for trail development, operation, and maintenance. In addition, several federal agencies involved with the trails signed a memorandum of understanding (MOU) in 2006 to coordinate federal trail management. In contrast to the NSTs and NHTs, NRTs are typically administered by states, localities, and private organizations, with federal agencies participating when the trails cross federal lands. The National Park Service is responsible for the overall coordination of the national recreation trails, including nonfederal trails. Nonfederal trail managers have access to federal training and technical assistance, and are eligible for some types of federal funding. Connecting or side trails are administered by the Secretary under whose jurisdiction the trail lands fall. The six existing trails are all administered by the Secretary of the Interior. The FY2013 annual report of the Federal Interagency Council on Trails discussed a number of management issues facing the agencies that administer the National Trails System. These issues included tight federal agency budgets, financial constraints among partner groups, inconsistent mapping, aging volunteers, and expansion of energy projects and the transmission grid in ways that affect the trails. Another challenge cited was the lack of awareness among many Americans of the system and its health, community, economic, and educational benefits. The administering Secretary may regulate the use of federally owned portions of the national trails, in consultation with relevant agencies. The Secretary may permit uses "which will not substantially interfere with the nature and purposes of the trail." Such uses may include but are not limited to bicycling, cross-country skiing, day hiking, equestrian activities, jogging or similar fitness activities, overnight and long-distance backpacking, snowmobiling, and surface water and underwater activities. The use of motorized vehicles by the general public is typically prohibited on national scenic trails. However, motorized vehicles may be allowed on national historic trails if they do not substantially interfere with the nature and purposes of the trail and were allowed by administrative regulations at the time of designation. Trail uses on nonfederal lands—whether segments of scenic, historic, recreation, or connecting trails—are typically controlled at the state and local levels. State, local, and private-sector trail managers may work together to develop cooperative principles for use and management.