Rail Banking is a Federal statute under the National Trails System Act administered through the Surface Transportation Board. http://www.stb.dot.gov The Federal government established the rail banking tool in recognition of the value of intact corridors and the great expense of assembling a similar corridor at a later date. A rail banked line remains intact and may be sold to another entity which may convert it to a public-use trail. Today, more than sixteen hundred public trails across the United States exist because of rail banking. (Find them at Rails-to-Trails Conservancy)
A rail banked corridor is subject to possible future restoration of rail service if it is ever deemed equitable. If restoration happens, the trail management entity receives just compensation for the value of the trail.
An article about legal issues about rail banking can be found at: