To ease the strain on the central Verbindungsbahn ("connection railway"), a second main connection was constructed, the City S-Bahn, which traverses the city centre in a tunnel. The first section was opened in 1975 between Hauptbahnhof and Landungsbrücken, the extension to Altona in 1979 and was completed in 1981 with the connection above ground to "Diebsteich". 1983 saw the opening of the line via Wilhelmsburg to "Harburg Rathaus", a long stretch of which runs along the existing mainline. Through Hammerbrook the trains run on a concrete viaduct and in a tunnel under the centre of Harburg. The line was extended in 1984 along the Niederelbebahn to Neugraben.