"Die Hochbahn auf einen Blick" [A View of the U-Bahn] (in German). Hamburger Hochbahn. 2012. Archived from the original on 21 October 2013. Retrieved 30 September 2013.
"Historie der Hochbahn" [History of the U-Bahn] (in German). Hamburger Hochbahn. 2013. Archived from the original on 21 October 2013. Retrieved 30 September 2013.
"Extension of the U4". Extension of the U4 (in German). Hamburger Hochbahn. Retrieved 19 September 2016.
"Die Hochbahn auf einen Blick" [A View of the U-Bahn] (in German). Hamburger Hochbahn. 2012. Archived from the original on 21 October 2013. Retrieved 30 September 2013.
"Historie der Hochbahn" [History of the U-Bahn] (in German). Hamburger Hochbahn. 2013. Archived from the original on 21 October 2013. Retrieved 30 September 2013.