If you see a thin plastic net across the road...

... don't try to drive through it.  It may be a "vehicle arrestor" from Barrier1 Systems ("Barrier1 provides engineering, fabrication, and installation of its products which include its net based reduced risk energy absorbing active vehicle barrier, shallow mount bollards, fixed & removable bollards, crash beam swing gate, electric drop arm gate, quick connect barrier, crash rated fencing, waterway arrestor, and other products.")

Via Geekologie.