The Berlin U-Bahn (; short for , "underground railway") is a rapid transit system in Berlin, the capital and largest city of Germany, and a major part of the city's public transport system. Together with the S-Bahn, a network of suburban train lines, and a tram network that operates mostly in the eastern parts of the city, it serves as the main means of transport in the capital.
Opened in 1902, the serves 175 stations spread across nine lines, with a total track length of , about 80% of which is underground. Trains run every two to five minutes during peak hours, every five minutes for the rest of the day and every ten minutes in the evening. Over the course of a year, U-Bahn trains travel , and carry over 400 million passengers. In 2017, 553.1 million passengers rode the U-Bahn. The entire system is maintained and operated by the , commonly known as the BVG.
Designed to alleviate traffic flowing into and out of central Berlin, the U-Bahn was rapidly expanded until the city was divided into East and West Berlin at the end of World War II. Although the system remained open to residents of both sides at first, the construction of the Berlin Wall and the subsequent restrictions imposed by East Germany limited travel across the border. The East Berlin U-Bahn lines from West Berlin were severed, except for two West Berlin lines that ran through East Berlin (U6 and U8). These were allowed to pass through East Berlin without stopping at any of the stations, which were closed. Friedrichstraße was the exception because it was used as a transfer point between U6 and the West Berlin S-Bahn system, and a border crossing into East Berlin. The system was reopened completely following the fall of the Berlin Wall and German reunification.
The Berlin U-Bahn is the most extensive underground network in Germany. In 2006, travel on the U-Bahn was equivalent to 122.2 million km (76 million mi) of car journeys.
History
The Berlin U-Bahn was built in three major phases: Up to 1913: the construction of the (small profile) network in Berlin, Charlottenburg, Schöneberg, and Wilmersdorf; Up to 1930: the introduction of the (large profile) network that established the first north–south lines; From 1953 on: further development after World War II.
In a bid to secure its own improvement, Schöneberg also wanted a connection to Berlin. The elevated railway company did not believe such a line would be profitable, so the city built the first locally financed underground in Germany (intentionally using standard of ). It was opened on 1 December 1910. Just a few months earlier, work began on a fourth line to link Wilmersdorf in the southwest to the growing Berlin U-Bahn.
The early network ran mostly east to west, connecting the richer areas in and around Berlin, as these routes had been deemed the most profitable. In order to open up the network to more of the workers of Berlin, the city wanted north–south lines to be established. In 1920, the surrounding areas were annexed to form Groß-Berlin ("Greater Berlin"), removing the need for many negotiations, and giving the city much greater bargaining power over the private ("elevated railway company"). The city also mandated that new lines would use wider carriages—running on the same, standard-gauge track—to provide greater passenger capacity; these became known as the Großprofil ("large profile") network.
Construction of the ("North-South railway") connecting Wedding in the north to Tempelhof and Neukölln in the south had started in December 1912, but halted for the First World War. Work resumed in 1919, although the money shortage caused by hyperinflation slowed progress considerably. On 30 January 1923, the first section opened between Hallesches Tor and Stettiner Bahnhof (Naturkundemuseum), with a continuation to Seestraße following two months later. Desperately underfunded, the new line had to use trains from the old Kleinprofil network; the carriages exits had to be widened to fill the gap to the platforms with wooden boards that passengers jokingly referred to as Blumenbretter ("boards for flower pots"). The line branched at Belle-Alliance-Straße, now (Mehringdamm); the continuation south to Tempelhof opened on 22 December 1929, the branch to Grenzallee on 21 December 1930.