There is a specialized equipment manufactuer here, that makes right-of-way clearing machines for utility companies as well as railroads. Some of their stuff is awesome. Our local electrical cooperative ahs a few large JD tractors all enclosed with expanded metal and steel bars, skid plates on the bottom and full roll bar wrap around protection and pull some super rotary cutters clearing the brush and such under and around the power lines. I looked at one the one day after it was parked and the crew gone home, and on the bottom was a steel disk of approximately 1 1/4" thickness, and it had carbide cutters in addition to short stubby swing blades to do the cutting. I guess that heavy steel plate acted like a flywheel, and also a stump jumper. They were hydraulic driven.
The one large railroad bed clearing machine I seen had two steel disks about 6 feet in diameter and maybe 2 inches thick loaded with carbide teeth that was mounted out in front. Off to the sides were rotating drums with what appeared to be short lengths of chain, that could be angled up or down or on an angle to sort of beat any brush and overhanging limbs into submissin. They use this beast to just drive through the brush and woods when they lay out a new set of tracks etc, and often run it down along the railroad bed as well. It looks like its built on a super heavy duty log skidder type chassis and is all rubber tires (6 of them) and the way its laid out looks like a road grader. It also had a hydraulic arm to work a hydraulic powered rotary cutter, that could reach out at least 30 to 40 feet in front or to the sides......one bad machine.
Kershaw Manufacturing is the companies name that makes that stuff here. The have machines from time to time out this way demonstrating them or prototyping them .