Life Hacks - How to charge a phone from the rail tracks. Measuring voltage on the railway.

With sorcery like this, how did the USSR ever fall?

Coded track circuits

A coded track circuit based system is essentially an inductive system that uses the running rails as information transmitter. The coded track circuits serve a dual purpose: to perform the train detection and rail continuity detection functions of a standard track circuit, and to continuously transmit signal indications to the train. The coded track circuit systems eliminate the need for specialized beacons.

https://en.wikipedia.org/wiki/Cab_signalling