Bischofsholer Damm. Whilst some preparations have been made, most notably an empty station under today's Hauptbahnhof station and a special arrangement of pillars at stations Steintor and Marienstraße to allow a tunnel to be built underneath, the plans could not be realised, due to the high costs. It would however have been greatly beneficial to the D line, reducing stepover times to other lines. The current surface D line between Goetheplatz and Aegidientorplatz is regarded as a permanent solution for the mid-term future, although this statement could be argued against, for example when the wye at Steintor was demolished after the tearing down of tram tracks that had been replaced by the C-Nord line, the points were not removed but just welded shut. During the renovation of the Hauptbahnhof in 1999 and 2000, the tram tracks in front of the station were not replaced either. üstra started undertaking major improvement works on the D line in 2017. This is called "Projekt zehn-siebzehn" (see below) and consists of renovating the existing surface line instead of building new tunnels. Dead tunnels Even though it is of a relatively young age, the Hanover Stadtbahn already has some buildings that are likely not to be used as intended. These are three tunnel stubs in the A and B tunnels. Under both the ramps Hammersteinstraße (A-Nord) and Vahrenwalder Platz (B-Nord) the tunnel continues until the ramp's end since the original U-Bahn plans had proposed an extension of the tunnels. Whilst this made some theoretical sense at the A-Nord due to the relatively narrow Podbielskistraße, an extension of the tunnel is completely unneeded on the rather wide Vahrenwalder Straße. The stubs currently house some technical service rooms. A notably larger structure exists behind the middle tracks of the station Waterloo. It was originally supposed to extend a tunnel toward the A-West (line 9 toward Empelde) and to construct a turning loop. However, this would require tearing down the current A-West ramp at Gustav-Bratke-Allee which would disconnect the Glocksee depot from the network. Thus, this will likely never be carried out. History Stadtbahn lines opened See also üstra intalliance AG TW 6000 TW 2000 TW 3000 Stadtbahn List of rapid transit systems References External links üstra Hannoversche Verkehrsbetriebe Großraum-Verkehr Hannover Stadtbahn/tram Hannover Light rail in Germany Underground rapid transit in Germany Tram transport in Germany Stadtbahn