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The Berlin U-Bahn (Untergrundbahn, underground railway) is a major part of the public transport system of the German capital, Berlin. Opened in 1902, the U-Bahn serves 170 stations spread across nine lines, with a total track length of 151.7 km, about 80% of which is underground. Trains run every two to five minutes during peak hours, and every seven to twelve minutes for the rest of the day; they travel 132 million km (83 million mi), carrying 400 million passengers, over the year. The entire system is maintained and operated by the Berliner Verkehrsbetriebe, commonly known as the BVG.

Designed to alleviate traffic flowing into and out of central Berlin, the U-Bahn rapidly expanded until the city was divided into East and West Berlin at the end of World War II. Although the system initially remained open to residents of both sides, the construction of the Berlin Wall and the subsequent restrictions imposed by the East German government limited travel across the border: East Germans were prevented from riding on the U-Bahn into West Berlin; while West Germans were permitted to use certain lines that ran through East German territory, but not to disembark. The system was reopened completely following the fall of the Berlin Wall, and German reunification.

As of 2007, the Berlin U-Bahn is the most extensive underground network in Germany. True to its original goal, it has been calculated that, in 2006, use of the U-Bahn amounted to the equivalent of 122.2 million km (76 million mi) of car journeys. Now thoroughly modernised after years of neglect during the Cold War, it serves as the main transportation method of the capital.

History
The construction of the Berlin U-Bahn occurred in three major phases:
 * 1) Up to 1913 – the construction of the Kleinprofil (small profile) network in Berlin, Charlottenburg, Schöneberg, and Wilmersdorf;
 * 2) Up to 1930 – the introduction of the Großprofil (large profile) network that established the first North-South lines;
 * 3) From 1953 on – further development after the Second World War.

Initial construction: 1896–1913


At the end of the 19th century, city planners in Berlin were looking for solutions to the increasing traffic problems facing the city. As potential solutions, industrialist and inventor Werner von Siemens suggested the construction of elevated railways, while AEG proposed an underground system. Berlin city administrators feared an underground would damage the sewers, favouring an elevated railway following the path of the former city walls; however, the neighbouring city of Charlottenburg did not share Berlin's fears, and disliked the idea of an elevated railway running along Tauentzienstraße. Years of negotiations followed until, on 10 September 1896, work began on a mostly-elevated railway to run between Stralauer Thor and Zoologischer Garten, with a short spur to Potsdamer Platz. Known as the "Stammstrecke", the route was inaugurated on 15 February, 1902, to immediate popularity. Before the year ended, the railway had been extended: by 17 August, east to Warschauer Brücke (Warschauer Straße); and, by 14 December, west to Knie (Ernst-Reuter-Platz).



Charlottenburg extended the line further westwards: by 1906, it had reached the town hall at Wilhelmplatz (Richard-Wagner-Platz); by 1908, Reichskanzlerplatz (Theodor-Heuss-Platz); and, by 3 November 1912, Sportpark (Olympia-Stadion). In Berlin's city centre, Potsdamer Platz was disconnected—to be replaced by Leipziger Platz (Potsdamer Platz)—to allow an extension to the spur. The line underneath Leipziger Straße to Spittelmarkt opened in 1908; it was extended to Alexanderplatz by July 1913, with the Wilhelmplatz–Alexanderplatz route swiftly become the most popular of the Berlin U-Bahn. Three-and-a-half weeks later, on 27 July 1913, the northern extension to Nordring (Schönhauser Allee) was also opened.

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 took it upon itself to build the first local underground in Germany. Running as a subsurface railway from Hauptstraße, the 2.9 km (1.8 mi) line needed a second, underground station at its Nollendorfplatz terminus, since the established station there was part of the elevated railway. The line took two years to construct; it was opened on 1 December 1910.

Just a few months earlier, work began on a fourth line to link Wilmersdorf in the south-west to the growing Berlin U-Bahn. Originally planned as a line from Wittenbergplatz to Breitenbachplatz, Wilmersdorf paid for the line to reach as far as Thielplatz. As a concession to Charlottenburg for travelling through the city, the construction of a track from Wittenbergplatz, under the Kurfürstendamm, to Uhlandstraße was also agreed upon. Both lines were opened on 12 October 1913; these were the last to open before the outbreak of the First World War—and the subsequent economic difficulties faced by Germany—that prevented any further additions to the Berlin U-Bahn for ten years.

Second construction phase: 1923–1930


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. Its wishes were strengthened when, in 1920, the surrounding areas were annexed in the formation of Groß-Berlin (Greater Berlin), removing the need for many negotiations, and giving the city much greater bargaining power over the private Hochbahngesellschaft (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 Nord-Süd-Bahn (North-South line)—to connect 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—between Hallesches Tor and Stettiner Bahnhof (Zinnowitzer Straße)—opened, with the continuation to Seestraße following two months later. Desperately underfunded, the new line had to use trains from the old Kleinprofil network; the carriages were widened to reach the platforms with wooden boards that passengers jokingly referred to as Blumenbretter (flower boards). The line branched at Belle-Alliance-Straße (Mehringdamm): the continuation south to Tempelhof opened on 22 December 1929; the branch to Grenzallee (Berlin U-Bahn), 21 December 1930.



In 1912, plans were approved for AEG to build its own north-south underground line. Named the GN-Bahn after its termini, it would connect Gesundbrunnen and Neukölln, via Alexanderplatz. Financial difficulties stopped the construction in 1919; the liquidation of AEG-Schnellbahn-AG, and Berlin's commitment to the Nord-Süd-Bahn, prevented any further development until 1926. The first section opened on 17 July 1927 between Boddinstraße and Schönleinstraße, with the intermediate Hermannplatz becoming the first station at which passengers could transfer between two different Großprofil lines. Sections to the north, which required the relocation of Kottbusser Tor, opened in stages. The completed route—from Gesundbrunnen to Leinestraße—opened on 18 April 1930.

Before control of the U-Bahn network was handed over completely to the BVG in 1929, the Hochbahngesellschaft started construction on a final line that, in contrast to its previous lines, was built as part of the Großprofil network. The E line would run under Frankfurter Allee—for which the company had received the concession in 1914—between Alexanderplatz and Friedrichsfelde. The construction work proceeded easily and without much expense, and established the first workshop in the east of the city; the line opened on 21 December 1930. The 1920s also saw a few other short extensions to U-Bahn lines, bringing the total track length to 76 km.

National Socialism and the Second World War: 1933–1945
The seizure of power by the National Socialists brought many changes that affected Germany, including the U-Bahn. Most remarkably, the national flag was hung in every station, and two of the stations were renamed: Reichskanzlerplatz became Adolf-Hitler-Platz on 24 April 1933; and Schönhauser Tor became Horst-Wessel-Platz on 1 May 1934. Extensive plans—mostly the work of architect Albert Speer—were drawn up that included the construction of a circular line crossing the established U-Bahn lines, and new lines or extensions to many outlying districts. Despite such grand plans, no U-Bahn development occurred.

During the Second World War, U-Bahn travel soared as car use fell, and many of the underground stations were used as air-raid shelters; however, Allied bombs damaged or destroyed large parts of the U-Bahn system. Although the damage was usually repaired fairly quickly, the reconstructions became more difficult as the war went on. Eventually, on 25 April 1945, the whole system ground to a halt when the power station supplying the network failed. A week later, the network endured its worst disaster after the North-South S-Bahn tunnel was flooded. At Friedrichstraße, the water poured into the underground tunnels, flooding 63 km of the U-Bahn. Countless individuals hiding in the underground shelters were drowned as a result.

East and West: 1945–1989
The war had damaged or destroyed much of the network; however, 69.5 km of track and 93 stations were in use by the end of 1945, and the reconstruction was completed in 1950. Nevertheless, the consequent division of Berlin into East and West sectors brought further changes to the U-Bahn. Although the network spanned all sectors, and residents had freedom of movement, West Berliners increasingly avoided the Soviet sector and, from 1953, loudspeakers on the trains gave warnings when approaching the border. Passage of East Germans into the Western sectors also became subject to restrictions imposed by their government.

Between 1953 and 1955, the 200-Kilometer-Plan was drawn up, detailing the future development of the U-Bahn, which would ultimately grow to 200 km. Extending the C line to span from Tegel to Alt-Mariendorf was considered the highest priority: the northern extension to Tegel was opened on 31 May 1958. In order to circumvent East Berlin, and provide rapid-transport connections to the densely populated areas in Steglitz, Wedding, and Reinickendorf, a third north–south line was needed. The first section of line G was built between Leopoldplatz and Spichernstraße, with the intention of extending it at both ends. It had been planned to open the G line on 2 September 1961, but an earlier opening on 28 August was forced by the announcement of the construction of the Berlin Wall.



The physical division of the city cut the A line in half, and shortened the B line by one stop, since the Warschauer Brücke terminal lay in East Berlin, which retained only the eastern half of the A line, and line E. West Berlin paid an annual fee of DM20 million to permit trains on the C and D lines to run through eastern territory, although the trains were not allowed to stop on their way: the former stops became Geisterbahnhöfe (ghost stations), patrolled by armed East-German border guards. Only at Friedrichstraße, a designated border crosing point, were passengers allowed to disembark. A further consequence of the Wall was that West Berliners, unwilling to help fund the Soviet-dominated state, boycotted the East-German-controlled S-Bahn, transferring instead to the U-Bahn.

In West Berlin, housing developments in Britz and Rudow demanded an extension to the CI line. The Grenzallee to Britz-Süd connection opened on 28 September 1963. Guidelines for underground development stipulated that all lines should be linear, with no branches. Thus the extension in the opposite direction from Mehringdamm to Möckernbrücke established a new line: H. "Line H" would never be used, however, as its opening on 28 February 1966 coincided with the redesignation of all lines in West Berlin. The new line was named U7, and the Tempelhof to Alt-Mariendorf section—opened the same day—completed the newly-designated U6.

Funds from the economically-successful West-German capital, Bonn, to West Berlin were plentiful, allowing major expansions to U-Bahn lines: the U9, from Rathaus Steglitz to Osloer Straße was opened on 30 April 1976; the U7 was further extended in six sections until it reached Rathaus Spandau on 1 October 1984; and the U8 was extended north from Gesundbrunnen, through the newly-built Osloer Straße, to Paracelsus-Bad, which opened on 27 April 1987. In contrast, additions to the East Berlin lines were not so forthcoming. In the 1970s, the E line was extended east to Tierpark, opening on 25 June 1973. East Berliners had to wait 15 years for another extension—first to Elsterwerdaer Platz, then on to Hönow by 1 July 1989, just a few months before the fall of the Berlin Wall.

Reunification: 1989 onwards


On 9 November 1989, following months of unrest, the travel restrictions placed upon East Germans were lifted. Tens of thousands of East Berliners heard the statement live on television and flooded the border checkpoints, demanding entry into West Berlin. Jannowitzbrücke, a former ghost station, was reopened two days later as an additional crossing point. Other stations on the U8 soon followed suit; by 1 July 1990, the day of official reunification, all border controls were removed.

The newly renamed East Berlin U-Bahn lines—A became U2, E became U5—took more time to reconnect. The U2 between Wittenbergplatz and Mohrenstraße required extensive work that included removing the M-Bahn, rebuilding stations, reopening a tunnel, and reclaiming Nollendorfplatz and Bülowstraße stations—which had been repurposed as a flea market, and a Turkish bazaar. The amalgamated line was finally reopened on 13 November 1993, leaving only one connection to reinstate: the U1/U15 line across the Oberbaumbrücke to Warschauer Straße. Though it would take another two years, the connection was eventually re-established, after 34 years of separation, on 14 October 1995.

In the decade following reunification, only three short extensions were made to U-Bahn lines. On the U8, a northern extension from Paracelsus-Bad to Wittenau opened on 24 September 1994 and, in the south, the Leinestraße to Hermannstraße section opened on 13 July 1996. The U2 was also extended: the Vinetastraße to Pankow connection opened on 16 September 2000.

Routes
Since 2004, the U-Bahn has consisted of the following nine lines:

The pre-war U-Bahn line designations consisted of letters, with added Roman numerals in case of line branchings. This system continued to be used into the 1960s on both sides.

After the erection of the wall, East Berlin was left with line E and the eastern half of line A. This oddity and the fact that the two line network was simple to navigate anyway, caused line designations to be gradually abandoned there over the years.

West Berlin abandoned the letter based system in 1966 and replaced it by line numbers 1 through 9, the system still in place today. The shortest line in this system was line 5 which consisted of two stops only (Deutsche Oper - Richard-Wagner-Platz). It was closed in 1970, to be replaced by an extension of line 7 which opened a few years later. This move freed line number 5. West Berlin BVG then decided to reserve this line number for East Berlin's line E in case of reunification - the only line that ran exclusively in East Berlin territory and was therefore not yet covered in the new West Berlin system.

In 1984, BVG became the operator of the West Berlin S-Bahn which until then had been operated by East Germany's Deutsche Reichsbahn. So they had to incorporate the S-Bahn into their line numbering system, and did so by using the method of West German transport systems by giving new line numbers prefixed by "S" to the S-Bahn, and adding the prefix "U" to the existing U-Bahn lines. So "line 1" became "U1" etc.

After Berlin's reunification in 1990, East Berlin's line E was renumbered U5, as had been planned. At the same time, the eastern half of line A became U2 like its western counterpart, even though at the time they were not yet connected. When U2 was actually rejoined in 1993, the western branches of U1 and U2 were swapped, and the U3 disappeared from the map. What had been U3 -- a short shuttle line between Uhlandstraße and Wittenbergplatz -- became part of the new U15, a line that in theory continued past Wittenbergplatz in parallel with U1, to Schlesisches Tor (and, when it was reopened in 1995, Warschauer Straße); in practice, particularly in off-peak hours, U15 was often operated as a shuttle identical to the old U3. In 2004, the full length of U15 was redesignated U1, and a new U3 was created from what had been the U1 west of Nollendorfplatz to Krumme Lanke. (This was the same route as the U2 until 1993, extended one station further east to Nollendorfplatz enable trains to be reversed).

Stations
Among Berlin's 170 U-Bahn stations there are many with especially striking architecture or unusual design characteristics:

Hermannplatz station resembles something of an U-Bahn cathedral. The platform area is 7 metres high, 132 metres long and 22 metres wide. It was built in connection with the construction of the first North-South Line (Nord-Süd-Bahn), now the U6. The architecturally important department store Karstadt adjacent to the station, was being constructed at the same time. Karstadt contributed a large sum of money towards the decoration of the station and was in return rewarded with direct access from the station to the store. Hermannplatz was also the first U-Bahn station in Berlin to be equipped with escalators. Today, Hermannplatz is a busy interchange between the U7 and U8.

Alexanderplatz station is another of the more notable U-Bahn stations in Berlin, as well as being an important interchange between three lines (U2, U5 and U8). The first part of the station was opened in 1913 along with an extension of today's U2 line. In the 1920s Alexanderplatz itself was completely redesigned, both above and below ground. The U-Bahn station was expanded to provide access to the new D (today's U8) and E (today's U5) lines, then under construction. The result was a station with a restrained blue-grey tiled colour-scheme and Berlin's first underground shopping facilities, designed by Alfred Grenander. Over the last few years Alexanderplatz station has in stages, been restored to its former glory, the work is due to finish in 2007.

Wittenbergplatz station is also very interesting. Opened in 1902 as a simple station with two side platforms to plans by Paul Wittig. The station was completely redesigned by Alfred Grenander in 1912, with five platform faces, accommodating two new lines, to Dahlem today's (U3) and to Kurfürstendamm, today's Uhlandstraße (Berlin U-Bahn) on the (U1). A provision for a sixth platform was included but has never been completed. The redesign also featured a new entrance building, which blended into the grand architectural styles of Wittenbergplatz and the nearby KaDeWe department store. The interior of the entrance building was again rebuilt after considerable war damage, this time in a contemporary 1950's style. This lasted until the early 1980s when the interior was retro-renovated back into its original style. Wittenbergplatz station was presented with a London style "Roundel type" station sign in 1952, the 50th Anniversary of the Berlin U-Bahn. Today's station is an interchange station between the U1, U2 and U3 lines.

The name of the Gleisdreieck (rail triangle) station is still reminiscent of a construction which can only be imagined today. The wye itself was built in the opening year 1902. Plans for a redesign were made soon after, because the wye was already obsolete. An accident on September 26 1908 which claimed 18 to 21 lives was the final straw. The redesign and expansion of the Turmbahnhof, during which the station was still used, took until 1912. After World War II the station was put back into service on October 21 (lower platform) and November 18 (upper platform) 1945. However, service was interrupted again by the construction of the Berlin Wall. From 1972 onwards no trains were running on the lower platform, because servicing the U2 was no longer profitable due to the parallel traffic on the U1. The lower platform was reactivated in 1983, when the test line of the M-Bahn was built from the Gleisdreieck to the Kemperplatz station. It was broken down again after the fall of the Berlin Wall, since it obstructed parts of the reopened U2. Since 1993 the U1 and U2 trains both service the station once more.

Tickets


Fares Overview, from BVG.de. Current Prices and Descriptions of all ride-pass fare types.

As of July 2007, Berlin public transit passes are available from many places, automated and non-automated, BVG, Bahn, and third-party authorized. The Ring-Bahn Line and the other S-Bahn lines are included, as are buses, Metro-Tram and Ferries: the single ride-pass is inclusive for all transportation considered part of the Berlin-Regional public transit system.

Ride-passes (tickets) are available in fare classes: Adult and Reduced. Children between the ages of six and 14, and large dogs, qualify for the reduced fare. Children below the age of six, and small dogs, travel free. There are no 'Senior Discounts'. Residents who have applied for and received a German Disability Identification card, showing 80% or more disability (ID's available from the Versorgungsamt, German Disability Office ), can ride without a pass, including an additional person (as a helper). The disability identification card must be in the owner's possession.

Residents: With unemployment in the east averaging 15%, another common fare class in Berlin is the S(ozial)-Class. These identification cards are cleared through the normal government offices, then fulfilled at a BVG ride-pass non-automated location. Provided either the Job Center (Arbeitsamt) for the resident who is out-of-work, or for people who cannot work/partially disabled, by the Sozialamt, the S-Class ride-passes normally restrict travel to the AB zones, and must be renewed (a new pass purchased at a non-automated location) on the 1st of the month.

Additional passes are available for those which want to bring their bicycle on the public transit. As of this writing, 4.70€ is the price of a bicycle day-pass, this is additional to the normal ride-pass. A bicycle-pass is included in the Student-class ride-pass, which is provided through the Universities.

For small dogs, ones which can be carried in hand, there is no additional fare requirement. For each large dog, a Reduced fare ride-pass must be purchased. Tourist Ride-passes, All-day, group passes, and season passes include a dog-fare.

BVG ride-passes are issued for specific periods of time, and most require validation with a stamping machine before they are valid for use. The validation shows the date and time of the first use, and from where the ticket was validated (in code), and therefore when the ticket expires. For example, once validated, an All-Day Pass allows unlimited use, but then expires at 3AM the following day. Unlike most other metro systems, tickets in Berlin are not checked before entering Tram-Metros, U-Bahn or S-Bahn stations. They are checked by the bus drivers upon entering. On the Metro, S-Bahn and U-Bahn, there are random spot checks inside by plainclothes traffic officers who have the right to demand to see each passengers ticket. Passengers found without a ticket or an expired/invalid ticket are fined: 40 Euros per incident. The passenger may be required to pay on the spot, and is required on the spot to give a valid address to mail the relevant fine notice to (it does not have to be in Germany). On the third incident, the BVG calls the offender to Court, as there is now a history of 'riding without paying'.


 * Fare zones


 * Berlin is a part of the Verkehrsverbund Berlin-Brandenburg (Berlin-Brandenburg Transit Authority, VBB), which means ticketing and fare systems are unified with that of the surrounding Brandenburg. Berlin is divided into three fare zones, known as A, B, and C. Zone A is the area in the centre of Berlin and is demarcated by the S-Bahn urban rail ring line. Zone B covers the rest of the area within the city borders, and Zone C is the surrounding Berlin. Zone C is divided into eight parts, each belonging to an administrative district. The Potsdam-Mittelmark area is included in the city district of Potsdam.


 * Tickets can be bought for specific fare zones, or multiple zones. Most passengers who live in Berlin buy AB farezone tickets, while commuters coming in from the suburbs need ABC farezone tickets. If a ticket not valid for travel in a tariff zone is checked by a ticket inspector, the passenger is subject to a fine.


 * Short-term tickets
 * Single-journey tickets (Einzeltickets) are issued for use within specific fare zones, namely AB, BC, and ABC. They are only valid for two hours after validation, and cannot be extended. The BVG also offers single-day tickets (Tageskarte), which are valid for the entire day when first validated until 3 a.m. the next morning.


 * Long-term tickets
 * Long-term paper tickets are issued with validity periods of seven days (7-Tage-Karte) or one month (Monatskarten). The BVG is in the process of introducing the plastic MetroCard as a yearly ticket that also has additional features. The Metrocard also permits passengers to make reservations for hire cars at specific times, for example on weekends. It is expected that plastic Metrocards without such features will be made available they are more durable and ecofriendly than the paper tickets.


 * Tourist passes
 * The BVG offers tickets directed specifically for non-resident tourists of Berlin called the WelcomeCard and CityTourCard . WelcomeCards are valid for either 48 or 72 hours, and can be used by one adult and up to three children between the ages of six and 14. WelcomeCards are valid in farezones ABC, and have the additional benefit of a reduction on entry fees to many museums and tourist attractions. See the Current Prices and Descriptions link for more information.

Underground facilities
A full GSM (GSM-900 and GSM-1800) mobile phone network for Germany's four carriers is in place throughout the U-Bahn's stations and tunnels. The system has operated since 1995 for the E-Plus network, though access to other service providers followed in the late 1990s; the Berlin U-Bahn was one of the first metro systems to allow mobile telephone use.

Many of the cars on the U-Bahn feature small flat screen displays that show news headlines from BZ, weekly weather forecasts, and ads for local businesses.

Most major interchange stations have large shopping concourses with banks, supermarkets, and fast food outlets.

Unused stations and tunnels
There are several stations, platforms and tunnels that were built in preparation for future U-Bahn extensions, as well as those that have been abandoned following planning changes. For example, platforms have already been provided for the planned "U3" at Potsdamer Platz on the planned line to Weißensee. It is unlikely that this line, which had the working title "U3" will ever be built, so the platforms have been partially converted into a location for events and exhibitions. The Line number "U3" has been subsequently been used to re-number the branch to Krumme Lanke, which was previously part of "U1".

Line D, today's U8, was originally intended to run directly under Dresdner Straße via Oranienplatz to Kottbusser Tor. This segment of tunnel was abandoned in favour of a slightly less direct route in order to provide the former Wertheim department store at Moritzplatz with a direct connection. This involved the construction of a 90 degree curve of the line between Moritzplatz and Kottbusser Tor stations. The construction of the tunnel under Dresdner Straße had only been partially completed before abandonment, leaving it with only one track. This tunnel is currently separated into three parts, as it was blocked by a concrete wall where it crossed the border between East and West Berlin. Another concrete wall separates this tunnel, which now houses a transformer for an electricity supplier, from the never-completed Oranienplatz Station which is located partially under the square of the same name.

Stralauer Tor was a station on the eastern bank of the Spree between Warschauer Straße and Schlesisches Tor stations, which was completely destroyed in World War II. It had been opened in 1902 and was renamed Osthafen in 1924. Today, only struts on the viaduct remain to indicate its location. In the post second World War period it was not thought necessary to rebuild the station, due its close proximity to Warschauer Straße station, also because of its location, directly on the border of the Soviet/American sectors. Although a Berlin map dated 1946 does show the station renamed as Besarinstraße after a Soviet General. This name was used later at another location.

Nürnberger Platz station was closed on July 1, 1959. It was replaced by two new stations on either side, Augsburger Straße as well as an interchange station to the U9 at Spichernstraße. Today, nothing remains of the station as a third track siding was constructed in its place.

Another tunnel, which once connected the U4 to its original depot and workshop at Otzenstraße (Schöneberg), is still in existence. The connection from Innsbrucker Platz station to the depot was severed when a deep level motorway subway was constructed in the early 1970s - however, the continuation of the tunnel at Eisackstraße is still in existence for a distance of 270 metres and now ends at the former junction to the workshop of the Schöneberg line.



Platforms at five stations, Rathaus Steglitz, Schloßstraße, Walther-Schreiber-Platz, Innsbrucker Platz, and Kleistpark, were provided for the planned but never constructed U10. The U10 platform at Kleistpark has been converted into office space for the BVG. The other U10 platforms remain unused and are not generally open to the public.

During the construction of Adenauerplatz (U7) station, which was built in conjunction with an underpass, platforms were also provided for a planned U1 extension from Uhlandstraße to Theodor-Heuss-Platz. A short tunnel section was also constructed in front of the Internationalen Congress Centrum (ICC), beneath the Messedamm/Neue Kantstraße junction. This tunnel was built concurrently with a pedestrian subway and was also intended for the planned extension of the U1. The tunnel section, approximately 60 metres long, ends at the location of the planned Messe station adjacent to Berlins central bus station (ZOB). Currently, the tunnel is used as a storage area for theater props.

At Jungfernheide station, double U-Bahn platforms similar to those at Schloßstraße were built for the planned extension of the U5. The unused platform sides are fenced off. The finished (U5) tunnel section which leads off towards Tegel airport is now used for firefighting exercises.

Future development
Berlin's chronic financial problems and stagnating population make any expansion not mandated by the Hauptstadtvertrag—the document that regulates the necessary changes to the city as the capital of Germany—unlikely. Furthermore, there is still great rivalry for construction money between the U-Bahn and the S-Bahn. After the construction boom that followed the reunification of the city, enthusiasm for further growth has cooled off; many people feel that Berlin's needs are adequately met by the present U- and S-Bahn. As of 2007, the only proposals receiving serious consideration aim to facilitate travel around the existing system, such as moving Warschauer Straße's U-Bahn station closer to its S-Bahn station.

There are several long-term plans for the U-Bahn that have no estimated time of completion, most of which involve closing short gaps between stations, enabling them to connect to other lines. The segment between Uhlandstraße and Wittenbergplatz might be built further along the Kurfürstendamm to connect to the U7 at Adenauerplatz; more ambitious plans call for this segment to be separated and expanded into its own line, running from Theodor-Heuss-Platz on the U2, through Potsdamer Platz and Alexanderplatz, before connecting with the S-Bahn at Greifswalder Straße, and ending at Weißensee. This new line was tentatively designated the U3 until December 2004.

In summary, the plans for the Berlin U-Bahn are:


 * U1
 * The U1 will be extended from its eastern terminus of Warschauer Straße to Frankfurter Tor on the U5.




 * U2
 * Following the extension of the U2 to Pankow in 2000, there are plans to continue on to Ossietzkyplatz. In the west, an extension is planned from Ruhleben to the U7 terminus, Rathaus Spandau—which already has platforms for the U2.


 * U3
 * There are plans to eventually connect the U3 with the S1 S-Bahn line at Mexikoplatz in the south-west. This is one of the most likely extensions if Berlin is ever able to solve its financial problems.


 * U4
 * An autobahn underpass makes a southern extension of the U4 unfeasible; however, a possible northern extension would reach Magdeburger Platz, where it would connect with the future line from Potsdamer Platz to the Kurfürstendamm.




 * U5 and U55
 * In 2008, the U55 will open, running from Berlin Hauptbahnhof to Brandenburger Tor. It is a provisional line; part of a long-planned extension of the U5 from Alexanderplatz to the new central station.  Its construction is mandated by the Hauptstadtvertrag, requiring all construction mentioned in it to be completed by 2020.  The BVG expects 100,000 passengers to take the U5 extension daily.


 * The U5 extension—known as the Kanzlerlinie (chancellor's line), as it will run through the government quarter—is planned to go through Berliner Rathaus, along Unter den Linden and the Pariser Platz, terminating at Berlin Hauptbahnhof. Plans to extend the U5 to Turmstraße on the U9, and to Jungfernheide on the U7 are considered urgent by the city government, but the extension is unlikely unless Tegel Airport is also expanded.


 * U6
 * This line is considered complete.


 * U7
 * An extension of the U7 to Schönefeld International Airport was long planned in conjunction with the renovation and expansion of the airport, but the line is no longer included in cost projections for the airport's enlargement, as the BVG concluded projected passenger numbers did not justify the expense. Plans see the U7 running in the north-west to Staaken.


 * U8
 * The U8 was extended in 1996 as far as Hermannstraße; further extensions to the south are not planned. In the north, extending to the crowded Märkisches Viertel has long been planned: construction of the station underneath the sports centre on the Senftenberger Ring has already been started.  In addition, a station between Rathaus Reinickendorf and Wittenau has been structurally prepared.  Named Alt-Wittenau, this station can be completed, should the need arise.


 * U9
 * Local residents have been waiting for an extension of the U9 to Lankwitz station for years, but there are no current plans to extend the line. A northern extension of the U9 to the future Pankow Kirche U2 station has been abandoned in favour of a tram line.

Trains


The Berlin U-Bahn uses 750-Volt DC electric trains that run on standard gauge (1435 mm) tracks. The first trains were based on trams; they had a width of 2.30 m, and took their power from overhead lines. To accommodate greater passenger numbers without lengthening the trains—which would require costly extended platforms—trains that ran on lines built after the First World War were required to be wider. The original trains and lines, which continued to operate, were designated Kleinprofil (small profile), and the newer, wider trains and lines were designated Großprofil (large profile). Großprofil trains are 2.65 m wide, and take their power from a third rail.

Although the two profiles are generally incompatible, Kleinprofil trains have been modified to run on Großprofil lines during two periods of economic difficulty. Between 1923 and 1927 on the Nord-Süd-Bahn, and between 1961 and 1978 on the E line, adapted Kleinprofil trains were used to compensate for the lack of new Großprofil trains: they were widened with wooden boards to reach the platforms; and had their power pickups adapted to accept power from the negatively-charged third rail, instead of positively-charged overhead lines.

As of 2007, Kleinprofil trains run on the U1, U2, U3, and U4 lines; and Großprofil trains operate on the U5, U55, U6, U7, U8, and U9 routes.

Kleinprofil (small profile)


Kleinprofil trains are 2.30 m wide, and 3.10 m high. When the U-Bahn opened in 1902, forty-two multiple units, and twenty-one railroad cars, with a top speed of 50 km/h, had been built at the Warschauer Brücke workshop. In contrast to the earlier test vehicles, seating was placed along the walls, facing inward, which was considered more comfortable. Until 1927, U-Bahn trains had smoking compartments and third-class carriages. The trains were first updated in 1928; A-II carriages were distinguished by only having three windows, and two sliding doors.

After the division of the city, West Berlin upgraded its U-Bahn trains more rapidly than did East Berlin. The A3 type, introduced in 1960, was modelled on the Großprofil D type, and received regular modifications every few years. Meanwhile, A-I and A-II trains operated exclusively in East Berlin until 1975, when G-I trains, which had a top speed of 70 km/h, started to travel the Thälmannplatz–Pankow route. These were superseded in 1988 by the G-I/1 type, which used couplings that were incompatible with the older G-I carriages.

Following reunification, the A3 type was again upgraded as the A3L92, the first Kleinprofil type to use three-phase electric power. In 2000, prototypes for a Kleinprofil variant of the H series were built; the HK differs from its Großprofil counterpart by not being fully interconnected—carriages are only interconnected within each of the two half-trains.

As of 2005, only trains of the HK, G-I/1 and A3(U/L) types are in active service.

Großprofil (large profile)


Großprofil trains are 2.65 m wide, and 3.40 m high. The first sixteen multiple units and eight ordinary carriages entered active service on the Nord-Süd-Bahn in 1924, after a year of using modified Kleinprofil trains. Designated B-I, the cars were 13.15 m long and each had three sliding doors; the large elliptical windows at the front of the train earned them the nickname, Tunneleulen (tunnel owls). Upgraded B-II trains were introduced in 1927, and continued to be used until 1969. The first 18-metre-long (59 ft) C-I trains were trialled in 1926, and two upgrades were produced before the end of the decade. The first U-Bahn trains to use aluminium in their construction, the C-IV types, were introduced in 1930. Many C-type trains were seized by Soviet forces in 1945, to be used in the Moscow Metro.

The first D-type trains, manufactured in 1957, were built from steel, making them very heavy and less efficient; however, the DL type that followed from 1965 used metals that were less dense, allowing a 26% reduction in weight. In East Berlin, D-type trains bought from the BVG were designated D-I. Difficulties there in trying to develop an E series of trains led, in 1962, to the conversion of S-Bahn type 168 trains for use on the E line. These E-III trains were desperately needed at the time to allow modified Kleinprofil trains to return to the increasingly-busy A line but, following reunification, high running costs led to their retirement in 1994.

In West Berlin, the successor to the D-type was the F-type, which debuted in 1973. They varied from other models in having seats that were perpendicular to the sides of the train; from 1980, they also became the first U-Bahn trains to use three-phase electricity. In 1995, the original seating arrangement returned as the H series took up service. H-type trains are characterised by the interconnection of carriages throughout the length of the train; and they can only be removed from the tracks at main service depots.

As of 2005, only F and H-type trains are in active service.

Depots


Depots of the Berlin U-Bahn fall into one of two classes: main workshops (Hauptwerkstätten, abbreviated as Hw); and service workshops (Betriebswerkstätten, abbreviated Bw). The main workshops are the only places where trains can be lifted from the tracks; they are used for the full inspections required every few years, and for any major work on trains. The service workshops only handle minor repairs and maintenance, such as replacing windows, or removing graffiti.

As of 2005, the only dedicated Kleinprofil depot is at Grunewald (Hw Gru/Bw Gru), which opened on 21 January 1913. The first Großprofil depot opened at Seestraße (Hw See/Bw See) in 1923, to service the Nord-Süd-Bahn. It has 17 tracks—2 for the main workshop, and 15 for the service workshop—but its inner-city location prevents any further expansion. Due to BVG budget cuts, the Seestraße depot also services Kleinprofil trains. Two further Großprofil service workshops are located at Friedrichsfelde (Bw Fri), and Britz-Süd (Bw Britz).

In the past, there were other workshops. The first opened in 1901 at Warschauer Brücke, and was the construction site for most of the early U-Bahn trains. The division of the U-Bahn network on 13 August 1961 forced its closure, although it was reopened in 1995 as a storage depot. A small depot operated at Krumme Lanke between 22 December 1929 and 1 May 1968; and, while the network was split, East Berlin's U-Bahn used the S-Bahn depot at Schöneweide, along with a small service workshop at Rosa-Luxemburg-Platz, which was closed following reunification.

Accidents
The Berlin U-Bahn ranks among the safest modes of transportation: its history features few accidents.



The most severe accident occurred at the original Gleisdreieck (rail triangle), where the main and branch lines were connected by switches that allowed the tracks to cross. On 26 September, 1908, a train driver missed a stop signal. As a result, two trains collided at the junction, and one fell off the viaduct. The accident killed eighteen people, and severely injured another twenty-one. Gleisdreieck's triangular layout had already been deemed unsuitable for future developments; this incident—and a later, less-serious one—triggered its reconstruction as a multi-level station, starting in 1912.

On 30 June 1965, a train with brake failure stopped on the G line—today's U9—between Zoologischer Garten and Hansaplatz. Unaware of the faulty train, a mechanic working at the Zoologischer Garten signal tower noticed that the leaving signal had been set to 'Stop' for a long time. Thinking it should be set to 'Go', after several attempts, he manually changed the signal, in defiance of regulations that strictly prohibited such actions. The following train, which had been waiting at Zoologischer Garten, then left the station on the same track. With emergency brakes unable to prevent the accident, the two trains collided. One passenger was killed in the crash, and 97 were injured. The mechanic was fined 600,000 DM.

Fires can be particularly dangerous and damaging within an underground system. In October 1972, two trains and a 200 m length of tunnel were completely destroyed when the trains caught fire; the reconstructed tunnel is clearly differentiated from the old one. Another train burned out in the connecting tunnel between Klosterstraße and Alexanderplatz in 1987. On 8 July 2000, the last car of a GI/I train suffered a short circuit, burning out at the rear of the Deutsche Oper station. The single exit of the station was unreachable, forcing the passengers to run through the tunnel to reach the next emergency exit. The fire also damaged the station, which remained closed until September. The Portuguese Ambassador, João Diogo Nunes Barata, presented the BVG with azulejos (tiled paintings), specially designed for the station, by the artist José de Guimarães. Installation of Portugal's gift to the city was completed on 30 October 2002.



As a consequence of the Deutsche Oper incident, BVG decided to post an employee at every station with only one exit until a second exit could be built. Over the following few years, many of those stations—including Britz-Süd, Schillingstraße, Viktoria-Luise-Platz, Uhlandstraße, and Theo. Heuss Platz—were refitted with additional exits. As of September 2007, the only remaining stations with no second exit are Sophie-Charlotte-Platz and Rudow. Despite these changes, several passenger organisations—such as Pro Bahn, and IGEB—demand that stations with exits in the middle of the platform are also fitted with additional emergency exits. Many stations are built this way; meeting those demands would place a heavy financial burden on both the BVG and the city.

The U6 saw a particularly costly, though casualty-free, incident on 25 March 2003. Scheduled repair work on the line limited the normal service to between Alt-Mariendorf and Kurt-Schumacher-Platz; one train then shuttled back and forth between Kurt-Schumacher-Platz and Holzhauser Straße, sharing a platform at Kurt-Schumacher-Platz with the normal-service trains departing for their return journey to Alt-Mariendorf. Needing to pass several stop signals on the shuttle service, the driver had been given special instructions how to proceed. Unfortunately, he ignored the signal at the entry to Kurt-Schumacher-Platz, and ploughed into the side of a train heading back to Alt-Mariendorf. The impact wrecked both trains, and caused considerable damage to the tracks. Normal service did not resume for two days, and the removal of the two wrecked trains—which, surprisingly, could still roll along the tracks—also took nearly 48 hours.

Films, music and merchandising
The Berlin U-Bahn has appeared in numerous films and music videos. Offering access to stations, tunnels, and trains, the BVG cooperates with film-makers, although a permit is required.

Whether set in Berlin or elsewhere, the U-Bahn has had at least a minor role in a large number of movies and television programmes, including Emil und die Detektive (2001), Otto – Der Film (1985), ''Peng! Du bist tot (1987) featuring Ingolf Lück, Run Lola Run'' (1998), and several Tatort episodes. The previously-unused Reichstag station was used to shoot scenes of the movies Resident Evil and Equilibrium.



Möbius 17, by Frank Esher Lämmer and Jo Preussler from Berlin, tells the story of an U-Bahn train that, caught in a Möbius strip, travels through alternate universes after a new line is built. Alexanderplatz station plays an essential role in Berlin Alexanderplatz—a film of thirteen hour-long chapters and one epilogue—produced in 1980 by Rainer Werner Fassbinder, based on the book by Döblin. The film's scenes feature a recreation of the station as it was in 1928—rather darker and dirtier than in the 21st century. In the surrealistic two-hour epilogue, Fassbinder transforms parts of the station into a slaughterhouse where people are killed and dissected.

Since 2001, the Berlin U-bahn has hosted the annual short-film festival Going Underground. Short films (up to 90 seconds long) are shown on the monitors found in many of the U-Bahn trains. Passengers onboard vote for the festival winner.

Sandy Mölling, former singer of the pop band No Angels, shot the video for her single "Unnatural Blonde" in the U-Bahn station Deutsche Oper. Kate Ryan, Overground, Böhse Onkelz, Xavier Naidoo, Die Fantastischen Vier, and the DJ duo Blank & Jones have all used the U-Bahn and its stations for their videos as well.

"Linie 1", a musical preformed by Berlin's Grips-Theater, is set completely in stations and trains of the Berlin U-Bahn; a movie version has also been produced.

In 2002, the BVG cooperated with design students in a project to create underwear with an U-Bahn theme, which, in English, they named "Underwear". They used the names of real stations that, in the context of underwear, appeared to be mild sexual double entendres: men's underpants bore labels with Rohrdamm (pipe dam), Onkel Toms Hütte (Uncle Tom's Cabin), and Krumme Lanke (crooked lake); the women's had Gleisdreieck (triangle track), and Jungfernheide (virgin heath). After the first series sold out quickly, several others were commissioned, such as Nothammer (emergency hammer), and Pendelverkehr (shuttle service; though Verkehr also means "intercourse"). They were retired from sale in 2004.