a frequency of 15 minutes in 2010. Since 2015 a new signal tower for the Citytunnel is installed at Frankfurt Hauptbahnhof which is going to replace the original signal tower operating since 1978 in 2018. Therefore, it is necessary to close the tunnel several times between 2015 and 2018 for between two and six weeks each, mostly during school holidays. The times of service closure are also used to modernize the stations in the tunnel. From July 31 to August 18, 2006, the mainline tunnel between the main station and Konstablerwache was completely closed to exchange 30 switches. On May 13, 2007, the served by the S2, new breakpoint Frankfurt Zeilsheim was opened, on 31 October 2008, operated by the S3, single-track breakpoint Schwalbach North. For the timetable change 2017/18, a continuous night traffic was introduced on weekends. Due to nocturnal blockages of the City Tunnel, the railways go in a first phase at night on modified lines: S1: Wiesbaden Hbf - Hochheim (Main) - Frankfurt-Höchst - Frankfurt (Main) Hbf - Frankfurt (Main) South - Offenbach (Main) Main Station - Rödermark-Ober-Roden S3: Frankfurt (Main) South - Langen (Hesse) - Darmstadt Hbf S4: Kronberg (Taunus) - Eschborn - Frankfurt (Main) West - Frankfurt (Main) Hbf S5: Friedrichsdorf - Bad Homburg - Oberursel (Taunus) - Frankfurt (Main) West - Frankfurt (Main) Hbf S8: Wiesbaden Hbf - Mainz central station - Rüsselsheim - Frankfurt airport - Frankfurt (Main) Hbf - Frankfurt (Main) south - Offenbach (Main) central station - Hanau central station From August 2018, the start of operations of the entire night traffic in the Citytunnel is planned. From December 2018 the S8/S9 will be 24/7 through the Citytunnel with a 30-minute frequency between 1:00am and 4:30am from Frankfurt Flughafen Regionalbahnhof to Konstablerwache (1:11am/4:11am from Konstablerwache to Frankfurt Flughafen Regionalbahnhof) and a 60-minute frequency between 12:49am and 3:49am from Wiesbaden Hbf and Hanau Hbf (1:46am/3:46am from Hanau Hbf to Wiesbaden Hbf) Bridges The S-Bahn crosses three of the four largest rivers in the region, with a total of nine bridges and a tunnel: The Rhine crosses the line S8 twice, namely over the Kaiserbrücke between Mainz-Nord and Wiesbaden-Ost and the South bridge between Mainz Roman Theater and Mainz-Gustavsburg train station. The Main crosses the S-Bahn in five places. All lines cross the river at least once. The S8 to Hanau crosses the Main three times (until Offenbach Ost only twice), the S9