What is the Third Rail? (Metros and Electrification)

November 24, 2025 4:48 pm

Quick Definition: Third Rail

The Third Rail is a method of providing electric power to a train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track.

Most commonly seen in metro systems (like the London Underground or New York Subway), the third rail allows for smaller tunnels because it doesn’t require overhead wires. However, it carries high voltage near the ground, posing a safety risk.

Why use Third Rail?

Pros	Cons
Tunnel Size: Allows for smaller, cheaper tunnels (no overhead space needed).	Safety: Dangerous for trespassers/workers.
Maintenance: More robust against wind and storms than wires.	Speed Limit: Contact shoes lose stability at high speeds (>160 km/h).
Aesthetics: No ugly wires in historic city centers.	Weather: Can ice over in winter, causing power loss.