Tatra KT4

The Tatra KT4 (KT stands for kloubová tramvaj, lit. 'articulated tram') is a short-articulated tram with four-axles developed by the Czech firm ČKD Tatra. The first pre-production vehicles entered service in Potsdam in 1975, with the first production vehicles in 1977. A total of 1,747 units were built, with initial deliveries to East Germany (GDR) and later to the Soviet Union (USSR) and SFR Yugoslavia. KT4 variants were built for both standard gauge and metre gauge tramways. Production of the KT4 tramcar was halted in 1991 due to worldwide economic and political changes at the time. Production was briefly resumed in 1997 to construct the last 20 units for Belgrade, Serbia. Since the start of the 1990s, many of the earliest production tramcars have gone through extensive refurbishment and rebuilding, including the replacement of folding doors and the installation of low-floor center sections. The design of the tram, being without a bogie over the joint necessitates a scissor joint connecting both bogies such that the center of mass does not shift catastrophically, especially when turning.