This is a process here in the United States by which abandoned rail lines are converted into multi-use trails. First, the line must be abandoned. For a railroad be abandoned, three things must happen:

  1. rail service must be discontinued
  2. the Surface Transportation Board approves the abandonment
  3. the fee schedules are canceled

After the line is abandoned, the railroad company will come through and remove all the ties and rails as part of a salvage operation. Generally, bridges and tunnels are left intact. Then, any interested trail agency may purchase the abandoned line. Sometimes, this is done through a process called railbanking where the railroad can sell, lease, or donate the abandoned line to a trail agency without the involvement of any other land owners. This is a provision of the National Trails System Act.

Once the line has been secured, the process of building the trail begins. This usually involves paving the rail line with asphalt, stone, wood chips, or whatever else is appropriate for the trail users. Decking and safety features are added to bridges. Road crossings are marked and signs are put up all over the place. Now the rail line has been converted into a trail suitable for hiking, cycling, horseback riding, and so forth.

Since the 1960s, almost 12,000 miles of trails have been created across the country. Some of these trails stretch for hundreds of miles across entire states. The majority of these very long trails are out in the Midwest though there's a trail in every state these days. Rails to trails have the advantage of either being flat or having a very low grade since trains used to ride over them. With some long trails and some short ones, there's pretty much something for everyone. They frequently run through or very close to parks, attaching to park trails as well.