some Euro-PCC trams in Belgium. American streetcars use either trolley poles or single-arm pantographs. Metro systems and overhead lines Most rapid transit systems are powered by a third rail, but some use pantographs, particularly ones that involve extensive above-ground running. Most hybrid metro-tram or 'pre-metro' lines whose routes include tracks on city streets or in other publicly accessible areas, such as (formerly) line 51 of the Amsterdam Metro, the MBTA Green Line, RTA Rapid Transit in Cleveland, Frankfurt am Main U-Bahn, and San Francisco's Muni Metro, use overhead wire, as a standard third rail would obstruct street traffic and present too great a risk of electrocution. Among the various exceptions are several tram systems, such as the ones in Bordeaux, Angers, Reims and Dubai that use a proprietary underground system developed by Alstom, called APS, which only applies power to segments of track that are completely covered by the tram. This system was originally designed to be used in the historic centre of Bordeaux because an overhead wire system would cause a visual intrusion. Similar systems that avoid overhead lines have been developed by Bombardier, AnsaldoBreda, CAF, and others. These may consist of physical ground-level infrastructure, or use energy stored in battery packs to travel over short distances without overhead wiring. Overhead pantographs are sometimes used as alternatives to third rails because third rails can ice over in certain winter weather conditions. The MBTA Blue Line uses pantograph power for the entire section of its route that runs on the surface, while switching to third rail power before entering the underground portion of its route. The entire metro systems of Sydney, Madrid, Barcelona, Shanghai, Hong Kong, Seoul, Kobe, Fukuoka, Sendai, Jaipur, Chennai, Mumbai and Delhi use overhead wiring and pantographs (as well as certain lines of the metro systems in Beijing, Chongqing, Noida, Hyderabad, Jakarta, Tokyo, Osaka, Nagoya, Singapore, Sapporo, Budapest, and Mexico City). Pantographs were also used on the Nord-Sud Company rapid transit lines in Paris until the other operating company of the time, Compagnie du chemin de fer métropolitain de Paris, bought out the company and replaced all overhead wiring with the standard third rail system used on other lines. Numerous railway lines use both third rail and overhead power collection along different portions of their routes, generally for historical reasons. They include the North London line and West London lines of London Overground, the Northern City Line