to Potsdamer Platz. This branch was protected only by signals, so that driver inattention could easily lead to a disaster, as happened on 26 September 1908. A U-Bahn train ran into the side of another train, forcing two carriages off the track. One carriage fell over the viaduct and 21 passengers died. As a result, it was decided to change the configuration at Gleisdreieck. Construction began in May 1912 to replace the triangular junction with two lines built as a grade-separated cross with a new Gleisdreieck interchange station at the intersection. These lines now form part of U1 and U2. The new work was carried out largely with full services operating, although services were briefly interrupted on each line. On 3 November 1912, the new Gleisdreieck station was opened but construction was not completed until August 1913. The connecting track from the Pankow direction to the Warschauer Straße direction continued to be open until the completion of work for use by construction supply trains. References Notes Bibliography U1 (Berlin U-Bahn) stations U2 (Berlin U-Bahn) stations U3 (Berlin U-Bahn) stations Buildings and structures in Friedrichshain-Kreuzberg Railway stations in Germany opened in 1902