page_title: Railway electrification system
section_title: Rubber-tyred systems
hierarchical_section_title: Railway electrification system / Direct current / Rubber-tyred systems
context_page_description: A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply.
  Electric railways use either electric locomotives, electric multiple units or both.
  Electricity is typically generated in large and relatively efficient generating stations, transmitted to the railway network and distributed to the trains. Some electric railways have their own dedicated generating stations and transmission lines, but most purchase power from an electric utility. The railway usually provides its own distribution lines, switches, and transformers.
  Power is supplied to moving trains with a continuous conductor running along the track that usually takes one of two forms: an overhead line, suspended from poles or towers along the track or from structure or tunnel ceilings, or a third rail mounted at track level and contacted by a sliding "pickup shoe". Both overhead wire and third-rail systems usually use the running rails as the return conductor, but some systems use a separate fourth rail for this purpose.
context_section_description: A few lines of the Paris Métro in France operate on a four-rail power system. The trains move on rubber tyres which roll on a pair of narrow roll ways made of steel and, in some places, of concrete. Since the tyres do not conduct the return current, the two guide bars provided outside the running 'roll ways' become, in a sense, a third and fourth rail which each provide 750 V DC, so at least electrically it is a four-rail system. Each wheel set of a powered bogie carries one traction motor. A side sliding (side running) contact shoe picks up the current from the vertical face of each guide bar. The return of each traction motor, as well as each wagon, is effected by one contact shoe each that slide on top of each one of the running rails. This and all other rubber-tyred metros that have a 1,435 mm (4 ft 8 ¹⁄₂ in) standard gauge track between the roll ways operate in the same manner.
caption: Bogie from an MP 89 Paris Métro vehicle. The lateral contact shoe is located between the rubber tyres
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