[andyv133]

Although not all rail systems in all countries use axle counters for presence detection. In the US freight industry we use track circuits - https://en.wikipedia.org/wiki/Track_circuit

[Symbiote]

That's not a replacement, that's the older technology.

Axle counting guarantees that there isn't a detached, derailed wagon fouling the line, or a wagon with dirty wheels which aren't completing the track circuit.

[andyv133]

Nonetheless, it is what is used on freight lines in the U.S quite successfully, and provides other protections such as broken rail detection.

Detached cars are detected using the FRED/braking system, and secondarily by axle counts given by hot box detectors read over the radio.