To qualify for an addition to the National Trails System, the historic trail must meet criteria provided by the National Trails System Act (NTSA). http://www.nps.gov/nts/legislation.html
NTSA criteria are:
• The trail must be established by historic use. In this case, the study must determine whether an Oregon Trail study segment was established by 19th-century emigrants traveling overland to the Oregon Country, today's Oregon and Washington. A trail might be important and historic for other reasons — exploration, military use, commercial and communications uses — but to be part of the Oregon National Historic Trail, it must have carried emigrant wagon traffic to Oregon.
• The trail must be historically significant as a result of that use. A trail might be significant because it was used by many emigrants; because it is associated with historically important parties or individuals; or because it is directly associated with important, well-known, or unique historical events.
• The trail must be of national significance, with far-reaching effects on broad patterns of American culture. An eligible route must demonstrate well-established use as a link in the Oregon Trail, which itself had "far-reaching effects on broad patterns of American culture."
• The location of the trail route must be sufficiently known. Educated guesses and speculation aren't enough. The trail's location must be reasonably well established by historic documentation (such as maps, 19th-century emigrant guides, pioneer journals, and sketches) or by traces (such as wagon ruts, artifacts, emigrant inscriptions, or well-known landmarks) on the ground.
• The trail must have significant potential for public recreational use or historical interest based on historic interpretation and appreciation. Are there historic sites and undisturbed segments of the trail that the public could visit? Do we have information about the trail, related historic sites, and historic events that could be shared with visitors at interpretive sites, roadside pullouts, and other venues? Could visitors retrace parts of the original route, especially through areas that retain their historic appearance? Are these areas open and accessible to the public, or if on private land, are they likely to be made available by landowners' consent?
Even if the NPS determines that a study segment meets these eligibility criteria, the segment might be found unfeasible due to costs, environmental or community impacts, public objections, or other concerns.