As with overhead wires, the return current usually flows through one or both running rails, and leakage to ground is not considered serious. Where trains run on rubber tyres, as on parts of the Lyon Metro, Paris Métro, Mexico City metro, Santiago Metro, Sapporo Municipal Subway, and on all of the Montreal Metro and some automated guideway transit systems (e.g. the Astram Line), a live rail must be provided to feed the current. The return is effected through the rails of the conventional track between these guide bars ("see rubber-tyred metro").