Similiar to what was seen in the James Bond movie.
I have never actually seen that used though. The only thing I have seen done is for them to go in and manually cut away the brush. I dont live up near Luray though(thats the location of the caverns).
Eitherway, they have those large lines crossing all over the state and they are required to have at least 10ft of clearance on eitehr side.(could be 20-30ft, but I seem to remember 10, perhaps thats by size of the line)
To climb the mountain, you must believe you can.