When the helicopter is initially going down, its' rotors clash with the railing on the overpass. A moment later, the same shot shows the helicopter on the ground, sideways and on fire, the railing on the overpass is intact. (the helicopter being brought down was done digitally, as was the railing being taken out).
Obviously, they did not bother to take out the railing for the second scene.
Obviously, they did not bother to take out the railing for the second scene.