That would be the Peninsula Crossing Trail just west of 6525 N Lombard St.
This is bad. I have seen transient cars drive on the trail. I bet stolen bikes are getting hauled around in derelict RVs.
By the way, this is where they give out meth pipes, drug syringes, and host a place for the people who utilize those services to cash out bottles and cans they have stolen from various places every Saturday afternoon.