Here's a street view link that should give you an idea:
https://www.google.com/maps/@40.705226,-73.995817,3a,90y,130...
- The bike+pedestrian path is suspended over the roadway.
- There are some suspension cables leading from the suspended pedestrian path, and trusses leading to the other cables.
- The cables are pretty thick and have railing-like cables, likely for maintenance.
- There is only a small metal door preventing people from running all the way up the cables. The railing-like cables look useful for climbing over the door.
It's possible that with the right skills, nothing is necessary but the new flag and tins, a plan, and a little luck.
Even with permits and DOT assistance, the SWAT team came out after them and halted traffic on the bridge.
Video of the walkway and cables, if I'm not mistaken.