By December 1981, all the sections of U1 originally included in the basic network (Reumannplatz - Stephansplatz - Praterstern, 6.1 kilometres in length[6]) were into operation.

The extension of line U1 to Kagran, 3.9 km (2.4 mi) long, which was not part of the original plans and was added later when the Reichsbrücke over the Danube collapsed in 1976, was completed in September 1982.

The change to the original plans was thought to be due cost issues or the incomplete development of the area surrounding Rothneusiedl.

[10] The extension was ultimately opened to the public on 2 September 2017, thereby expanding the Vienna metro network by 4.6 km (2.9 mi) and 5 stations.

In addition, the trains were retrofitted with plastic seats, video surveillance and warning lights that had signalled the door closing.