English: A train of Milan Metro's Line 1 (M1 or Red Line). The contact shoe for the fourth-rail feeding system can be seen between the axles. The fourth-rail system has two standard rails (standard gauge), a centre rail called "third rail" and a lateral, elevated rail called "fourth rail". The third and the fourth rail carry electric power, while the standard rails are at ground potential. The power is collected by the train through contact shoes.
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