What is the fundamental difference between third rail and overhead line electrification for railways?

The fundamental difference lies in how electric power is delivered to the train. A third rail system uses a semi-continuous rigid conductor rail placed alongside the tracks, typically carrying direct current (DC) at a lower voltage (e.g., 750V). The train draws power through a "contact shoe" that slides along this rail. In contrast, an overhead line system, also known as a catenary system, uses a network of wires suspended above the tracks. The train collects power from these wires using a pantograph mounted on its roof, and these systems often operate with higher-voltage alternating current (AC).