coverings are missing, which is because the complete station already suffered from water damage in the 1970s (and, to a smaller extent, still frequently does so today) and it was necessary to remove those segments in order to fix the leaking ceiling and walls. This also had to be done at the U2 platforms, but as those have been in service, the coverings were mounted to the walls again after all repairs were finished. Current projects In 2015 major subway extension plans were published. They include building a new branch from Horner Rennbahn to Horner Geest with two stations, transferring the eastern terminus of the U4 from Billstedt to the new branch terminus building a whole new U5 line running from Osdorfer Born in the west of Hamburg to Bramfeld in the east via Uhlenhorst, representing a modified and extended version of the old U4 plans from the 1970s. The first part of the route is intended to be built between Sengelmannstrasse and Bramfeld between 2022 and 2028. Original plans also called for the U4 to be extended southward to the S-Bahn station Harburg Rathaus via Wilhelmsburg, in order to provide a second rapid transit line to serve the south of Hamburg and relieve the busy S3/S31 that is - since its opening in 1983 - the only rapid transit service for the complete borough of Harburg and nowadays operates at its capacity limit. These plans are subject of discussions in 2018 still, no actual plans have been made so far. However, the new Elbbrücken station has been constructed in a way that allows a further extension of the line in the future. Network The Hamburg U-Bahn consists of four lines: The line names U1 und U2 were introduced with the timetable change on 22 May 1966, the name U3 followed on 2 January 1967. Until the completion of the direct inner-city stretch, the future U2, on 3 June 1973, the partial services on the already completed eastern (Hauptbahnhof Nord − Berliner Tor (− Barmbek) since 29 September 1968) and western (Schlump − Gänsemarkt since 31 May 1970) sections were known as U21 and U22 respectively. U4 project Hamburger Hochbahn opened the new line U4 in November 2012. There had been an ongoing discussion about the costs and the benefit of this line, but the government of Hamburg decided to build it nevertheless. The underground line was dug using the