Vienna has a rich and long history of tramways and different systems of such. Tramways usually run on the surface not separated from other traffic but in the 1960s Vienna put some portions of its system under the earth. These portions are called "UStraBa" which stands for "Unterpflasterstraßenbahn" meaning "tramway running under the street". There were two sections of which only the one under parts of the Gürtel is still in use while the other one under the Lastenstraße was cut off from the rest of the tramway system and than converted to a new subway line (U2) in the 80s. Losing its connection to the street level system made it an isolated and very short line for many years meaning more transfers whereas before that for a cross city trip none was necessary.
In the late 1970s there was also a pre-metro line - like today's light rail lines - which existed for some years before it was finally converted to a subway line (U6) in 1995.
All three systems are shown below. Any feedback is appreciated.
