The Stadtbahn is a concept dating back as far as the late 1940s, when city councils were considering Unterpflasterstraßenbahn (lit. below-pavement tramways) as part of rebuilding the city centres devastated by World War II. Some cities, like Hanover, reserved extra wide medians in their city's ring roads, though in most cities these plans never made it past the planning stage. However, seeing the success of the Berlin and Hamburg U-Bahn systems, cities started considering such schemes again in the 1960s and 1970s. Munich and Nuremberg decided to fully abolish their trams and started constructing a full-scale U-Bahn system (although to date, neither of these has abolished their tram system and likely never will) whilst other cities, like Hanover or Stuttgart, went for a scheme of city centre tunnels and special right-of-way arrangements with the prospect of converting their tramway networks to a full-fledged U-Bahn over several decades. By the 1980s, however, virtually all cities had abolished these plans due to the high costs involved with converting the tramways, and the most common Stadtbahn systems now are a mixture of tramway-like operations in suburban and peripheral areas, and a more U-Bahn like mode of operation, featuring tunnel stations, in the city centres.
The Stadtbahn scheme is not to be confused with the S-Bahn, which commonly is a suburban railway operating under the Railways Act, while the Stadtbahn typically is an urban railway operating under the Tramways Act.
The most common vehicle type currently in use in Germany is the articulated tram, either in its high floor or low floor variant. Articulated trams are tram cars that consist of several sections held together by flexible joints. Like articulated buses, they have an increased passenger capacity. These trams can be up to forty metres in length, while a regular tram has to be much shorter.
From 1918 on, a few prototypes were built in Germany, for example a trailer car for Dresden in 1918 and two tramcars with Jacobs bogies for Duisburg in 1926. However, interest for these cars was low and the concept of articulation fell into obscurity.
It was only after World War II that articulated cars were manufactured again; the first, small series of GT4 Jacobs bogie cars was deployed for Stuttgart in 1953 by Maschinenfabrik Esslingen. From 1956 on, Düsseldorfer Waggonfabrik (Düwag) manufactured large numbers of articulated tram cars for operators in Germany and abroad to replace old pre-war models.
Starting in 1959, Maschinenfabrik Esslingen and Hansawaggon, the latter mainly in Bremen and in Munich, tried to get into the market with their Kurzgelenkwagen construction — however, in West Germany their market share remained small compared to the Jacobs bogie cars made by Düwag. The Hansawaggon design was copied later by CKD Tatra, which manufactured large numbers of KT4D tram cars based on this design for use in the GDR.
Apart from the larger series, small numbers of cars were rebuilt for operators with odd requirements, for example the Bremer Straßenbahn AG received a series of 3-axled and Augsburg bought several 5-axled cars.
The GT4, developed by Maschinenfabrik Esslingen in 1959 for the Stuttgart tramways' steep lines connects the two bogies with a girder. The car bodies support themselves by resting on their bogie and on the girder. It therefore is not possible to separate the vehicle's individual cars. 380 cars were built in total, of which 350 were delivered to Stuttgart. Further cars were in use in Freiburg im Breisgau, Reutlingen, Neunkirchen as well as Ulm and Augsburg (which bought them used from Stuttgart), after German reunification used GT4 vehicles were also used in Nordhausen, Halberstadt and Halle.
The Hansawaggon cars, designed and built for Bremer Straßenbahn AG, rest on the individual carbody's bogie only. The joint is not supported, and sections can be added and removed in the workshop. Hansawaggon delivered articulated power cars and trailers to the tramways of Bremen and Bremerhaven, the Munich-based manufacturer Rathgeber bought these cars under licence for the Munich tramways.
The Czechoslovakian company CKD Tatra developed the KT4D tram car based on the same joint and bogie concept and delivered it in large numbers to the GDR from 1976. These cars, used in East Berlin and a number of other cities, were only manufactured as power cars, however they can run as multiple units.
This concept found another use in three- and four-part low floor trams built since 1989, however a special track layout is necessary for these trams, as they have the tendency to swerve in curves. MAN and Adtranz delivered these vehicles to Bremen, Berlin and Munich; Düwag built a series of 40 for Frankfurt am Main (Type R).