Although the general public thinks of a corridor as being "owned" by a railroad, in reality the average rail right-of-way is often a hodgepodge of conflicting ownership interests, which may begin to unravel upon abandonment of the right-of-way. The railroad may own outright some portions of the corridor (which were acquired in "fee simple"), while it may have only the right to use other portions (which are held in "easement").
Determining actual ownership requires a title search, which can be both complicated and time consuming. Preferably, a knowledgeable professional (usually a lawyer) will conduct the title search, either for the railroad, for an interested government body, or as a volunteer for a rail-trail advocacy group. However, if a professional is not already conducting a search, here is a thumbnail guide to conducting one on your own.