Hedge trimmers vary wildly in their ability to cut such things. My Ego monster battery one does pretty well (it also cuts through railway semaphore signal wires rather easily, oops)
Short of being unhelpful by suggesting a WW2 tank with a dozer blade (still mostly petrol driven), my next best solution would be a brushcutter blade on a heavy duty strimmer. Bloody lethal things, though. (but our railway permits them with simple training, so maybe you'd be OK.)