Regionalstadtbahn
The concept of Regionalstadtbahnen (also known by RegioStadtbahn or other names) arose as a result of the harmonisation or integration of railway lines into Stadtbahn networks. In the area of Cologne–Bonn a single operational system (of so-called above ground lines or Hochflurstrecken) was created by the Cologne Stadtbahn and the Stadtbahn Bonn, opened in 1974, from the conversion of two former railway lines (the Rheinuferbahn and Vorgebirgsbahn belonging to the old Köln-Bonner Eisenbahnen). Further developments led to tram-train networks that rather resembled an S-Bahn. This idea was first realised in 1992 in Karlsruhe (Stadtbahn Karlsruhe), where as part of the Karlsruhe model even so-called dual system railbuses were used, which in addition to the direct current of Straßenbahn lines (750 V) could also draw power from the 15-kV-alternating current from normal DB catenary. In Karlsruhe this network reached as far as Heilbronn, 84 kilometres (52 mi) away, where a Stadtbahn network was created going out from this line. Both in Karlsruhe and in Heilbronn the Stadtbahn filled both the roles of a classic tramway system as well as an S-Bahn. The Karlsruhe mixed-operation concept was also adopted by the Saarbahn in Saarbrücken. This model is today referred to in France as the tram-train.
Other Stadtbahn networks in Germany without tunnels, but which incorporate railway lines, are found in:
- Kassel (RegioTram Kassel with hybrid railcars for the transition between electrified and non-electrified routes)
- Zwickau (Diesel railbuses of the Vogtlandbahn on tramways in the city centre)
- Chemnitz (Variotrams fitted with railway equipment, which City-Bahn Chemnitz runs daily on the Chemnitz - Stollberg/Erzgeb. line)
- Gotha (Straßenbahn Gotha/Thüringerwaldbahn), above ground tramway (24 km long), in existence since 1924, to Waltershausen, Friedrichroda and Tabarz
- Nordhausen in the South Harz. This network run by the Harz Narrow Gauge Railways is notable because it supplements the diesel-hybrid cars with steam engines.
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