2000, the low-floor technology have been increasingly improved. Since 2001, the market leader Bombardier has been producing eight-axle three-piece rather than six-axle single-axle engines. And as successor model of the ADtranz low floor tram, is the Flexity Berlin. Particularly long-range low-floor articulation trains are built for the Dresden transport companies. At a time when low-floor technology is already almost standard, on the other hand the railways as RegioTrams also use railways, tramway vehicles (increasingly known as tramway vehicles) have to fulfill contradictory requirements. Kurzgelenkwagen Kurzgelenkwagen is a German term for articulated cars that require exactly one bogie per carbody. These are mostly of the GT4 type; a German acronym for an articulated (G for Gelenk = "joint") motorized (T for Triebwagen) tramcar with 4 axles. Two different models of these have been deployed: Type Stuttgart 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. Type Bremen The GT4 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. Tatra KT4 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; Duewag built a series of 40 for