Düsseldorf has 570,000 inhabitants and is the capital of the German Bundesland North-Rhine Westphalia. Extending on both sides of the river Rhine, Düsseldorf was included in the general 1970 Stadtbahn network designed for the Rhine-Ruhr area. For the city of Düsseldorf this project included mainly one 4-track east-west tunnel through the city centre which would split into two branches east of the central station (Düsseldorf Hauptbahnhof). One branch continues east towards Düsseldorf-Eller and the second (2 km) runs southeast to Düsseldorf-Oberbilk and further south along the existing route to Holthausen. North of Heinrich-Heine-Allee the central trunk route also splits into two branches, one crosses the river Rhine on the Oberkassel Bridge towards Neuss and Krefeld, and the other one continues underground to Victoriaplatz/Klever Straße and then on the surface along the upgraded route of interurban tram line D towards Duisburg. Now there are 11 underground stations in Düsseldorf.