They are implemented pretty much on all the routes which have signalling systems, but it is not utilized fully, like having automatic blocks and automatic signalling. In many railway systems, track circuits are also used to monitor the track conditions. It is quite possible to upgrade the track circuits to automatically turn signals to red upon detecting a broken piece of track, and with some advanced features, it is possible to identify large irregularities like an incompletely sawn-off track. IR did some experiments with such signalling systems on some routes, but mostly the equipment was stolen.