Hamburg is the second largest city in Germany with approx. 1. 8 million inhabitants. The U-Bahn (underground) network has an extension of some 105 kilometres and is served by four lines (U1-U4). About 60 percent of the ways run overground (mainly on dams and viaducts) and only approx. 40 percent in tunnels.
The Hamburg U-Bahn and the city buses are operated by → "Hamburger Hochbahn AG"