Modern services on rapid transit systems are provided on designated lines between stations typically using electric multiple units on rail tracks, although some systems use guided rubber tires, magnetic levitation, or monorail. The stations typically have high platforms, without steps inside the trains, requiring custom-made trains in order to minimize gaps between train and platform. They are typically integrated with other public transport and often operated by the same public transport authorities. However, some rapid transit systems have at-grade intersections between a rapid transit line and a road or between two rapid transit lines.
Metro is the most common term for underground rapid transit systems used by non-native English speakers. Rapid transit systems may be named after the medium by which passengers travel in busy central business districts; the use of tunnels inspires names such as subway,underground,Untergrundbahn (U-Bahn) in German, or the Tunnelbana (T-bana) in Swedish; the use of viaducts inspires names such as elevated (L or el), skytrain,overhead, overground or Hochbahn in German. One of these terms may apply to an entire system, even if a large part of the network (for example, in outer suburbs) runs at ground level.