Global Positioning Systems are facilitating the mapping of trails that were once rails and the Rails to Trails Conservancy is asking for volunteers to use GPS systems to help them create a national online map of trails (http://www.traillink.com/gps.aspx ). A by-product of the rails to trails program has been the development of rails with trails. This occurs when a railroad retains use of the right of way, but works with an organization to develop a recreational trail along the same corridor. This approach raises different safety concerns (see http://www.fhwa.dot.gov/environment/rectrails/rwt/ ) than the rails to trails, but echoes the desire of recreational users to have access to these areas. In the words of author Danaya C. Wright, the rails-to-trails program "has raised some of the most contested property disputes of the late twentieth and early twenty-first centuries." For analysis of the issues behind such disputes, see Professor Wright's chapter in Powell on Real Property® published by Lexis, Rails-to-Trails: Conversion of Railroad Corridors to Recreational Trails (10-78A Powell on Real Property 78A.syn Powell on Real Property ) and her expert commentary (Danaya C. Wright on Hash v. United States Hash v. United States, 403 F.3d 1308 (Fed. Cir. 2005)).