The U-Bahn Line B is the second line in the network of the Frankfurt U-Bahn. It leads in west–east direction from the central railway station (Hauptbahnhof) over the old town to Konstablerwache, where it splits into two branches to Bornheim (U4 service) and Preungesheim (U5 service). Originally planned as an independent main line, the D line represents an extension of the U4 to Bockenheimer Warte from the central railway station.
The northern branch to Preungesheim was opened in 1974 and was used by the B1 service, and since May 1978 by U5. A large part of the route consists of a former tram line, which runs in Eckenheimer highway on street-level railway track. The platforms were also very low on the parts of the track, meaning that only the converted Ptb trams could run on the line. From 2013 to 2016, the above ground stations were developed barrier-free. Since 9 October 2016 the subway cars type U5 run on the U5 service.
Inaugurated in 1980, the U4 runs between Bockenheim and Bornheim exclusively on independent railway tracks and in tunnels. In 2008, the line was extended beyond the existing terminus Seckbacher road on existing tracks by the depot East to Schäfflestraße in the district Riederwald and drove for the first time also partially above ground. In December 2008, this trial operation went into regular operation, with the line extended to Enkheim. Every second to third train of the U4 goes there on a special track in the course of the Borsigallee, the existing above-ground tracks of the C line together with the U7 service. Since then, the U4, like the other Frankfurt underground services, has not been independent of individual traffic on the entire route.
List of sections
The B-line can be divided into three sections: in the common line used by the U4 and U5 between the main train station and Konstablerwache and in two route branches, in which the trunk line branches out at the Konstablerwache. Shortly after this central station leaves the U5 Scheffeleck the B-line and the tunnel, while the U4 continues in the direction of Bornheim. The densely built downtown area is not left. Until the former final stop Seckbacher Landstraße the route runs completely underground. Thus, the trains of the U4, which turn at this station, are the only exclusively subterranean moving light rail in Frankfurt.
The U4 also travels parts of the C and D line: It does not end like the U5 at the central railway station, but drives in addition as the only Stadtbahn line the stations Festhalle / Messe and Bockenheimer Warte the D-line. This almost two-kilometer long piece is the (after the opening of the Riedberg clasp of the U8 and U9 (2010)) the second youngest section in the subway network, opened in 2001. The U4 has also been extended at the other end of the B line: since December 14, 2008, some of their trains have entered part of the C line via the depot of the East depot until the final stop at Enkheim on the U7. (As a test, the service had already been extended from June to December 2008 to Schäfflestraße station.)
Officially, the B-line is divided into sections as follows. These are usually numbered with Roman numerals; however, connecting lines use Arabic numbers:
The main section
Below the station forecourt and the subterranean shopping arcade below there is the four-track underground station Hauptbahnhof, which was built as a community station for the B and D lines. It has two middle platforms, which are to be driven according to long-term planning from the north–south line D and the east–west line B in the direction of operation. At present, however, only the eastern branch of the B line and the northern branch of the D line exist, which are therefore continuously used by the U4 until further notice. The U4 to Bockenheim and the terminating U5 use the inner track of the station. Starting at the Hauptbahnhof the U5 runs since the commissioning of the extension of the U4 to Bockenheimer waiting in the direction Preungesheim the other inner track, the outer western track is used by the U4 to Bornheim. The eastern outer track is intended for the previously unrealized southern D line and since the opening of the station out of service. At the central station, the most important regional transport hub in the region, there is a transition to the suburban S-Bahn, whose tunnel station is below the subway station, tram, city and regional buses as well as regional and long-distance traffic.