A line post anchoring device for a roadway cable barrier system includes a lower helical anchor to which a detachable line post socket member is secured. The helical anchor and line post socket of each line post anchoring device have mating coupling sections that are preassembled and hydraulically screwed into the ground in a single operation. Each socket includes interior guide plates for properly guiding and positioning a line post therein, such that the cabling system can be effectively strung under tension at the same time the anchoring devices are installed in the ground. Damaged sockets are easily replaced with minimal disruption to the surrounding soil by backing the helical anchor out of the ground only so far as necessary to detach and replace the damaged socket, and then reinserting the helical anchor in the same location. There is no delay or multiple operations required for installation or repair, thus enhancing roadway safety by minimizing traffic disruptions and possible accidents incident thereto.