12 December 2010 in operation: The line U8 leaves from the South Station, connected via the A-trunk line, to the Riedberg and ends there. It absorbs most of the traffic as long as section D II does not exist. In addition, there is for the first time a line with the U9, which runs mainly on the D route. The U9 runs from Ginnheim to the northern end of the Line D on the Riedberg and on the Line A to Nieder-Eschbach. Other Details The starting point of the D route is the underground station Hauptbahnhof. This was already opened in 1978 as a preliminary end point of the B-line and has four arranged on the same level tracks, which are accessed via two island platforms. The station extends in a north-south direction under the station forecourt and is crossed by the underlying tracks of the City Tunnel approximately at right angles. The trains of lines U4 and U5 currently use only the two middle and the west track, while the eastern track is only one-sided connected to the existing routes and therefore can not be used in scheduled operation. The Line D connects to the station in a northerly direction and follows Düsseldorfer Straße to Platz der Republik, while the tracks of the Line B branch off to the west. The existing tunnel stump is currently being used as a turning facility for the U5 line, and is due to be extended to Europaviertel by 2019. The D-Tunnel continues to follow the Friedrich-Ebert-Anlage, where after a short time the underground station Festhalle / Messe is reached. The station was equipped with an extremely wide platform, taking into account the expected number of passengers at fairs. The platform hall itself has double storey height and is lit by two glass cones at street level with daylight. Planned route to Rebstock: Behind the station are two short tunnel stumps, which were originally intended as an advance payment for a subway line into the Rebstock area. However, this connection was made in 2003 for reasons of cost by a tram line. Immediately afterwards, the two single-track line tunnels turn northwest and follow the Senckenberganlage up to the terminus Bockenheimer Warte. Immediately in front of the station branches off from the city-leading track in an easterly direction from a single-track line tunnel, which establishes a track connection to the overlying C-section. It is