- The network started with the north-south running U1, the only really new subway line for a long time to come. New stretches were opened quickly and reached the right bank of the Danube River in 1982, crossing the river via the reconstructed Imperial Bridge. 2006 saw its last extensions.
- The southwest-northeast U2 started as a tram tunnel in 1966. It was converted to an U-Bahn line in 1980, connecting with U4 at both ends to form a circle around the central city. An eastward extension in 2008 to the football stadium doubled the length of the line, and in 2010 it became the third U-Bahn line to bridge the Danube.
- An east-west U3 line was built from 1991 to 2000.
- The modern U4 developed from the outer knee of the former Stadtbahn which was converted from light rail to subway standard form 1976 and 1981 for that matter and still features many Belle Epoque stations from the start, most notably the Hietzing station near Schönbrunn Castle.
- The U5 doesn't exist yet, but parts of the central loop of the U2 line will be broken off from it in order to extended into the northwest, crossing its former mother line at City Hall.
- The U6 developed from the north-south Belt Line of the former Stadtbahn, starting in 1989 and finishing in 1996. The southern extension was originally built as a light rail line in the late 1970s. Because the central section is an architectually significant viaduct designed in the Jugendstil era by Otto Wagner, it couldn't be upgraded to full U-Bahn standard and is still operated by tram-like vehicles with overhead wire.
Useful Notes / Vienna U And S Bahn
Vienna as the capital of Austria has often been considered one of the best cities in the world to live in. Reasons for this are versatile: Low social conflict, cultural experience, a well-maintained natural environment, and last but not least an extensive system of public transport maintained by the Wiener Linien, the eponymous Lines of Vienna. Cue some Early Installment Weirdness however, even if Vienna features a comparably young subway system because it's actually Older Than They Think as its precedessor was the Stadtbahn opened in 1898 and built with heavy rail perimeters. Those parts that would much later turn into subway lines (U4 and U6) were given to the city of Vienna in 1924 and got thoroughly electrified and put into service as a light rail in 1925, complete with a fare union with the tramway. The S-Bahn Vienna has also had an inner-city underground railroad link since 1873 with an overground predecessor from 1859 on, but it's only been used for S-Bahn-typical crossrail services since 1962, first as the Schnellbahn (rapid rail) and from 2005 as S-Bahn as anywhere else. It proved to be an even better subway after Vienna's Imperial Bridge collapsed early in the morning without warning at August 1st, 1976, running on a 7½-minute headway that was doubled at rush hour. The U-Bahn Digging and conversion for the U-Bahn started in 1969, grand opening was in 1978.