beginning. When other cities started implementing their systems in the 1960s, they mostly had to use the existing intercity rail tracks, and they still more or less use such tracks. The central intercity stations of Frankfurt, Leipzig, Munich and Stuttgart are terminal stations, so all four cities have monocentric S-Bahn networks. The S-Bahn trains use a tunnel under the central station and the city centre. The high number of large cities in the Ruhr area promotes a polycentric network connecting all cities and suburbs. The S-Bahn Rhein-Ruhr, as it is called, features few tunnels, and its routes are longer than those of other networks. The Ruhr S-Bahn is the only S-Bahn network to be run by more than one corporation in Germany, and the Salzburg S-Bahn holds a similar distinction in Austria. Most Swiss S-Bahn systems are multi-corporation networks, however. Most German S-Bahn networks have a unique ticket system, separated from the Deutsche Bahn rates, instead connected to the city ticket system used for U-bahns and local buses. The S-Bahn of Hanover, however, operates under five different rates due to its large expanse. One S-Bahn system is no longer in operation: the Erfurt S-Bahn which operated from 1976 until 1993 and was an single-line system which consisted of four stations from Erfurt Central Station to Erfurt Berliner Straße station in the then newly built northern suburbs of Erfurt. There are several S-Bahn or S-Bahn-like systems in planning, such as the Danube-Iller S-Bahn and the Augsburg S-Bahn. The S-Bahn system in Lübeck is under discussion (see network plan). The Stadtbahn Karlsruhe (a tram-train network) uses the green "S" logo, but does not refer to itself as S-Bahn. The blue U-Bahn logo is not used either, due to the lack of subterranean lines. Despite its name, the Ortenau S-Bahn (Offenburg) is a Regionalbahn service. The following networks are currently in operation: Switzerland and Liechtenstein S-Bahn is also used in the German-speaking part of Switzerland. While French publications of those networks translate it as RER, the line numbers are still prefixed with an S (e.g., as S2), except for the Léman Express, which uses the prefix "L" (e.g., as L2). S-Bahn-style services in the Italian and Romansh speaking parts of Switzerland also use the "S" prefix, although in Italian such networks are called rete celere (lit. fast network) instead of S-Bahn. The oldest network in Switzerland is the Bern S-Bahn, which was established