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be argued against, for example when the wye at "Steintor" was demolished after the tearing down of tram tracks that had been replaced by the C-Nord line, the points were not removed but just welded shut.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.