"More than 80 miles of the Great American Rail-Trail are in development right now across 10 states from Washington, D.C., to Washington state, adding roughly 50 miles to more than 2,000 miles of pre-existing trails across 12 states. The project, which bridges about 95 gaps between more than 145 trails, promises a multi-use cross-country trail that stretches more than 3,700 miles."
UPDATE: Here is the original/source website: railstotrails.org
"Picture yourself... pedaling across the entire country on a safe, seamless and scenic pathway -- or walking a local trail that connects along historic routes. Imagine the incomparable experience of exploring America's heritage by trail -- its potential, its beauty and bounty, its people and places. Consider the economic opportunities and the benefits for communities along the route of a multiuse trail that stretches more than 3,700 miles between Washington and Washington. Learn more about the vision of the Great American Rail-Trail."