Rails-to-Trails (or rail trails) are roads without cars. They are where railways go when they die. Bicycles love them.
Every year 2,000 miles of railways in the US are abandoned. So far, about half of the 300,000 miles railways built by 1916 (the railroad peak) have been taken out of service. Some 13,000 of those miles have been repurposed into bike/hike trails.
Why they’re great: 1) You get paths with flat to gentle slopes, 2) no cars, 3) no strip development, and 4) often passing through small towns. These wide, sculpted, relaxing paths are perfect for hiking, horseback, cross-country skiing, skates and particularly bicycles. While most of the rails-to-trails are less than 5 miles long, there are 10 in the country stretching over 100 miles and at least one that is 225 continuous miles. These longer trails are a big hit — easy, civilized bicycle tours: gentle rides without having to compete with cars. As far as I am concerned, riding bicycles on rail trails is the way to go.
The rails to trails movement began in the mid-west, where most of the abandoned railways were. It has now spread to every state. There are about 1,300 rails-to-trails in the US, with another 1,000 in progress. Backpackers have a network of fabulously signed and maintained long-distance footpath trails; we now have the beginnings of a network of long-distance dedicated bikepaths.
Behind most of this work is the very effective non-profit Rails-to-Trails Conservancy. They publish a magazine, newsletter, and a directory of known rail trails in the US, entitled 1000 Great Rail Trails. It’s a bare bones listing with no traveling information; but it is where you go to browse where rail trails exist in particular states. The same info, in slightly less useful search-mode is available on their supplemental website, TrailLink, which includes a list of the 10 longest rail trails, and introductory orientations to most rail trails.
For utilitarian logistical details, the Conservancy publishes 8 region-specific books. I’ve been using the California one, Rails-to-Trails: California. It covers about 60 rail trails in the state, including several in my own area that I was not aware of.