U55 (Berlin U-Bahn)

A train at Bundestag station

The unusual nature of U55 reflected Berlin's troubled finances. When the German government decided to move from Bonn to Berlin under the Chancellor of Germany Helmut Kohl, who also announced the reunification of Germany on 3 October 1990, it was decided to refurbish the area around the Bundestag into a modern government complex.

As part of this effort, there were plans to extend the U5 from its western terminus at Alexanderplatz through the city centre, past the Brandenburg Gate and the Bundestag, to the new central train station, Berlin Hauptbahnhof. This Kanzlerlinie (Chancellor Line), so nicknamed because it passed through the government quarter, was originally planned since the 200km plan as a diagonal line through central Berlin, continuing to Turmstraße in Moabit, where it would link with the U9, and on to Jungfernheide, where it would connect with the S-Bahn ring and U7. The line was also planned to go via Tegel Airport (to be replaced by Urban Tech Republic), Scharnweberstraße towards Rathaus Reinckendorf. As this was a long-planned route, short tunnels exist at both Jungfernheide and Turmstraße to accommodate the new line. Plans were discarded as a tram was also planned to be extended west. For now, the line is only approved to terminate at the Hauptbahnhof, with the route to Jungfernheide and beyond to be built later.

Berlin Hauptbahnhof U-Bahn station, under construction

On 19 January 2000, construction began on the western end of this extension. However, around that time the city council suffered a major financial crisis.

The city had accepted money from the German federal government for the construction work already finished, and by the terms of the agreement, the city would have had to return the money if there were no operating trains on the line. In 2004, the city and federal governments reached a compromise: the city would complete the short section of line that was largely complete between Berlin Hauptbahnhof and Unter den Linden S-Bahn station (renamed "Brandenburger Tor" in 2009) and run it as a single-track shuttle with a single train, without any signaling. Although transit planners projected that such a shuttle would not attract a significant ridership, the city determined that the cost of building and operating the line would be less than the cost of returning the money to the federal government.

The opening of the line between Berlin Hauptbahnhof and Brandenburger Tor was delayed owing to extreme groundwater problems at the site of the latter new station. It was finally opened on 8 August 2009.[5]

With the opening of the U-Bahn station, the existing Unter den Linden S-Bahn station was renamed Brandenburger Tor (for the nearby Brandenburg Gate). The name "Unter den Linden" was then given to a new station further east at the junction with Friedrichstraße, where the U5 intersects the U6.

The train ran every 10 minutes and, due to the low demand, there was no night service.

Car is delivered through tunnel opening.

Because the U55 was not physically connected to the rest of the U-Bahn system, any trains being delivered to the new line had to be taken by low loaders on the street and set on track through a tunnel opening located north of Hauptbahnhof station. There was also a provisional workshop for the basic maintenance and cleaning of carriages.

Formerly, trains running on the U55 were F79 trains. However, due to a lack of trains on other large profile U-Bahn lines, the two U55 trains were removed and placed on the U6 in April 2017. Instead, an older D class train was renovated and placed into service until March 2020.