U3 is a line on the Berlin U-Bahn created in its current version on 12 December 2004.
The routing is largely the same as the previous U2 until 1993, but it runs from Krumme Lanke to Wittenbergplatz. The route was renumbered to U1 from 1993 to 2004. It was extended one station further east to Nollendorfplatz to enable trains to be reversed and to allow one-stop transfer to the U4 in 2003.
In the south, there are plans to extend the U3 towards the Berlin Mexikoplatz station, and going via Lindenthaler Allee, Bhf Düppel, Hakenheide, Förster-Funke-Allee and towards Machnower Schleuse. Even though this would only take 700 meter of new tracks, the tight budgetary situation of the Berlin Senate hinders the realisation.
Train frequencies were running at 5 minutes on weekdays, 10 minutes on weekends and since 2006, a 15-minute night service was offered on weekends, and "N3" was offered during weekday nights.
Until 1993 U3 referred to the section of line between Wittenbergplatz and Uhlandstraße, it was formerly numbered B II (until 1957), B IV (from 1957 to 1966) and Line 3 (from 1966 to 1984), just before renaming to 'U3'. In 1993, this section was renumbered to U15 and became a branch of the U1.
With the change of train numbers in December 2004, there were some confusion can now arise, as the planned final phase of the U3 line from Theodor-Heuss-Platz via Westkreuz, Adenauerplatz, Kurfürstendamm, Wittenbergplatz, Lutzowplatz, Potsdamer Platz and Leipziger Straße to Alexanderplatz, and from there on to Weißensee and Karow-Ost, will overlap with the present course of the U3, as the provisional name would be with driverless Alstom Metropolis trains to be purchased for the U3. However, this plans were shelved and scrapped.