Third rail
type of electricity transmission of railways, particularly common in metro networks, one pole has a third rail, and the other pole is grounded and connected to the two primary rails / From Wikipedia, the free encyclopedia
A third rail is a metal railway track that is placed on either side of a train track to provide electrical power to trains traveling along the tracks.[1] They are often used on subways and local train services.[2] Before third rails, electricity was carried in overhead wires.[2]