Risk Management and Trail Insurance
http://www.railstotrails.org/build-trails/trail-building-toolbox/trail-building-management/liability-and-trail-insurance/

The primary focuses of rail-trail managers should be the safety of trail users and the minimization of risk and liability exposure. Liability insurance is a necessary requirement for trail owners/managers.

In most cases, the trail is owned by a government entity with an umbrella insurance policy that protects municipal activities and facilities. In which case, public liability risks from trails are small compared to the liability risks of roads, playgrounds and swimming pools. But when non-governmental organizations own trails, they should purchase a similar comprehensive liability insurance policy.

Recreational Use Statutes
There are recreational use statutes in all 50 states that protect private landowners who allow public access to their property— as when a trail crosses or abuts private property. Under these statutes, no landowner is liable for recreational injuries resulting from trail user carelessness if they have provided public access to their land for recreational purposes.

Even with recreational use statues, it is recommended that trail managers have agreements with private landowners that include liability insurance on these properties as well.