Urban trail systems across the country have shown benfits to their communities in many ways. Here are links to articles about these benefits:
New York City's Transportation
Commissioner says bicycle lanes improve safety for everyone.
An article in the International Police Mountain Bike Association Newsletter says police bike traffic improves exerciser's safety.
An article in the American Journal of Preventive Medicine links the health benefits of urban trails and physical activity.
Here is a survey of users and the economic impact of the Armstrong Trail that stretches 34.8 miles across three counties in Pennsylvania.
Here is another user survey and economic impact report for the Schuykill River Trail that covers 56 miles from Pottsville to Philadelphia, Pennsylvania.
Here is a study in the Journal of Injury Prevention that analyses how motorized traffic discourages walking and bicycling.