It is already done and almost on all routes that use signalling systems. Almost all main lines ( and many branch lines) use track circuit systems to control signals. You can see these beside the tracks in many places. Little black boxes which contain the electrical relays and at regular distances, a large silver colored cabinet containing batteries for the track circuits ( these boxes are usually labelled as B.Box). However, there seems to be something missing in this. May be the track circuits are not designed for maximum redundancy, but it's very puzzling why they track sabotage doesn't seem to affect the track circuits.