Spanning 15 states and the District of Columbia, the East Coast Greenway trail network eventually will link scores of local greenways from Canada to Key West, Florida -- nearly 3,000 miles.

"An urban version of the Appalachian Trail," said Dennis Markatos-Soriano, executive director of the East Coast Greenway Alliance.

The alliance, which is spearheading the effort, will hold its Spring Summit in Philadelphia to take stock of its accomplishments, plan ahead, and celebrate Philly's effort in the project.

"Philadelphia has been so good to work with. The Streets Department, Parks and Rec, the Mayor's Office of Transportation -- they've accomplished a lot," said Andrew Hamilton, Mid-Atlantic coordinator for the alliance.

Audio story produced by Kimberly Haas