Those TTT posts are explained literally in the first 3 posts of every single thread here including this one.
Those are to stop motorists from even considering trying to drive across it.
This is the Monon High Bridge Trail. There have been numerous links shared to the local trail system and numerous videos, so if you wanted to check it out in more detail that should be easy to do. In fact, 1.5 seconds of googling grabbed me this to share with you.
http://www.indianatrails.com/?q=content/monon-high-bridge-trail-delphi
It is open to the public. It is well traveled and well used. IT is a common hang out for local teens.