||This article needs additional citations for verification. (January 2012)|
|Transport Organisation||Rhein-Main-Verkehrsverbund (RMV)|
|Total length||about 303 km|
|Population in the area covered||about 3,400,000|
|Customers per day||about 400,000|
|Highest frequency||15 Min.|
|Rollstock||DB Class 420, DBAG Class 423, DBAG Class 430 (from 2014)|
The Rhine-Main S-Bahn system is an integrated rapid transit and commuter transport system for the Frankfurt/Rhine-Main region, which includes the cities Frankfurt am Main, Wiesbaden, Mainz, Offenbach am Main, Hanau and Darmstadt. The network comprises nine S-Bahn lines, eight of which currently travel through the cornerstone of the system, an underground tunnel (the "Citytunnel") through central Frankfurt. The first section of this tunnel was opened on May 28, 1978. Further tunnel sections were opened in 1983 and 1990, before its completion in 1992. The system belongs to the Rhein-Main-Verkehrsverbund (RMV) and is operated by DB Regio AG, a subsidiary of Deutsche Bahn AG.
End-to-end journey times on the nine lines in the system range from 36 minutes (on line S7) up to 87 minutes (on line S1). The longest journey time into central Frankfurt (Hauptwache), from any point on the network, is 54 minutes. Services on some lines start shortly after 4 a.m, while all lines have services from about 5 a.m. onwards. A full service is maintained from 6 a.m. until about 8 p.m., and a somewhat reduced service is run until the late evening. The last services leave Frankfurt at about 1:20 a.m.
The S-Bahn system is quite closely integrated with other components of the region's transport system, such as the bus services in the various cities and towns, the tram services in Mainz, Frankfurt and Darmstadt, and the Frankfurt U-Bahn system. In Frankfurt, connections can be made, at either Hauptwache or its neighbouring station Konstablerwache, between the eight cross-city S-Bahn lines and eight of the city's nine U-Bahn lines, while the S-Bahn stations Frankfurt Hauptbahnhof and Frankfurt Süd between them have connection to six of the U-Bahn lines and any of the city's tram lines. Some opportunities for interchange also exist in the suburbs of Frankfurt.
Since the end of 2003, the system comprises the following lines:
|Wiesbaden – Frankfurt-Höchst – Frankfurt – Citytunnel – Offenbach Ost – Rödermark-Ober Roden|
|Niedernhausen – Frankfurt-Höchst – Frankfurt – Citytunnel – Offenbach Ost – Dietzenbach|
|Bad Soden – Frankfurt-West – Frankfurt – Citytunnel – Langen – Darmstadt|
|Kronberg – Frankfurt-West – Frankfurt – Citytunnel – Langen (– Darmstadt)|
|Friedrichsdorf – Frankfurt-West – Frankfurt – Citytunnel – Frankfurt-Süd|
|Friedberg – Frankfurt-West – Frankfurt – Citytunnel – Frankfurt-Süd|
|Riedstadt-Goddelau – Groß-Gerau Dornberg – Frankfurt Hauptbahnhof|
|Wiesbaden – Mainz – Frankfurt Airport – Frankfurt – Citytunnel – Offenbach Ost – Hanau|
|Wiesbaden – Mainz-Kastel – Frankfurt Airport – Frankfurt – Citytunnel – Offenbach Ost – Hanau|
The Early Years 
Plans for a rail connection between the central rail station (Hauptbahnhof) in Frankfurt and the Hauptwache, the central commuter destination in the city, were started in the early 1960s. Construction work on the project started in 1969. During the construction phase, some rearrangements were carried out to the commuter network in the area around Frankfurt, including creation of a link line between Bad Soden am Taunus and Niederhöchstadt.
In 1978 the first section of the "Citytunnel" of the Rhine-Main S-Bahn was opened, with all lines sharing the tunnel between Hauptbahnhof and Hauptwache. The initial system, which lay entirely to the north of the river Main, comprised the following lines:
- S1: Wiesbaden Hbf – Höchst – Hauptbahnhof – Hauptwache
- S2: Niedernhausen – Höchst – Hauptbahnhof – Hauptwache
- S3: Frankfurt-Höchst – Bad Soden – Frankfurt West – Hauptbahnhof – Hauptwache
- S4: Kronberg – Frankfurt West – Hauptbahnhof – Hauptwache
- S5: Friedrichsdorf – Frankfurt West – Hauptbahnhof – Hauptwache
- S6: Friedberg – Frankfurt West – Hauptbahnhof – Hauptwache
In 1980, two further lines were added to the network, made possible by construction of a new rail bridge over the river Main:
- S14: Wiesbaden – Mainz – Flughafen – Hauptbahnhof (main arrivals hall)
- S15: Flughafen – Hauptbahnhof – Hauptwache
Completion in 1983 of a 600m long easterly extension of the Citytunnel, as far as Konstablerwache, improved the opportunities for train turnaround in the tunnel. At this stage lines S1–S6 and line S14 were extended to Konstablerwache, while the S15 was rerouted to the main arrivals hall of the Hauptbahnhof.
Later Developments 
In 1990 the Citytunnel was extended, adding the underground stations Ostendstrasse and Lokalbahnhof to the system, along with the overground station Frankfurt Süd. All the lines (with the exception of the S15) were extended to Frankfurt Süd, while the S5 and S6 were further extended a short time later to a new station at Stresemannallee, south-west of Frankfurt Süd.
In 1992, S1 and S2 trains were diverted to the new Mühlberg underground station, the first station in the direction of Offenbach. This left the S3, S4, S5 and S6 serving all the stations between Hauptbahnhof and Frankfurt Süd, a situation which still pertains to this day. The S14, which is now the S8, also served all of these stations. In 1995, the newly instituted RMV increased train frequency from a 20/40/60 minute schedule (depending on the time of day) to the 15/30/60 minute schedule which is still used in the system. The S15 ceased operations at this stage.
Also in 1995, a new underground alignment through the city of Offenbach was opened, assisting the rerouting of the S14 (renamed the S8) through Mühlberg to City-Tunnel Offenbach and Hanau. The S1 was also extended as far as Offenbach, while the S2 returned to serving Frankfurt Süd. In 1997, the routes of the S5 and S6 were shortened slightly, so that they travelled only as far as Frankfurt Süd, while the S3 and S4 were extended to Darmstadt and Langen. The section of the S3 between Höchst and Bad Soden im Taunus also ceased to be served by S-Bahn trains.
In 1999, the S8 was effectively divided into two lines, the S8 and S9, both of which travel between Hanau and Wiesbaden via Bischofsheim. The S8 continues to travel through the centre of Mainz, while the S9 travels via Mainz-Kastel. This arrangement means that it is possible to travel between Wiesbaden, the capital of the state of Hesse, and Frankfurt, the state's largest city, by three different routes. In the same year, a new station on lines S3-S6 was opened in the Frankfurt fairground (Frankfurt Messe station).
In 2002, a new S-Bahn line, the S7, between Frankfurt Hauptbahnhof (main arrivals hall) and Riedstadt-Goddelau was added to the system (replacing the regional train line on the northern part of the Riedbahn). Due to a shortage of capacity in the Citytunnel, these trains are not currently able to reach Frankfurt's inner city. At present, these trains do not operate on a 30 minute schedule because of several ICE lines that operate on the same tracks.
In 2003 the Rodgaubahn, a commuter rail system serving Offenbach and its environs, was incorporated into the Rhine-Main S-Bahn system. This resulted in the S1 being extended from Offenbach Ost to Rödermark-Ober Roden, while the S2 was also rerouted from Frankfurt Süd to serve Offenbach Ost and all stations to its new terminus in Dietzenbach.
The current system has an almost 5-minute frequency for services between Frankfurt and Offenbach Ost and an actual 5-minute frequency for services between Frankfurt Hauptbahnhof and Frankfurt Süd. The group of lines S1, S2, S8 and S9 all share 10 stations, as do the group of lines S3, S4, S5 and S6. All the lines, with the exception of the S7, share 5 stations. Initially this arrangement gave rise to some considerable delays caused by poorly functioning signalling. To some extent this has been allayed by routing every second westbound S2 train in peak times to Offenbach am Main (Hauptbahnhof) and every second eastbound S2 train in peak times to the main arrivals hall of the Frankfurt Hauptbahnhof, rather than running these services through the Citytunnel. Reconstruction of the signalling technology in the Citytunnel would enable all westbound S2 trains to travel all the way to Niedernhausen at a frequency of 15 minutes.
The future 
Current plans for the system include a line to Hanau via Maintal, largely running north of the river Main. This would extend the S7 from Riedstadt-Goddelau, that currently terminates in the main hall of the Hauptbahnhof, with a service to and from Fechenheim (replacing the station at Mainkur) four times an hour of which half would extend to and from Hanau.
Some new stations are being contemplated to serve thriving localities including:
Problems and Accidents 
The biggest problem experienced on the Rhine-Main S-Bahn is frequent unpunctuality, one reason for which is the shortage of capacity in the Citytunnel. Capacity of the tunnel was increased from 22 trains per hour (in each direction) to 24 trains per hour in 2008 by optimising the Punktförmige Zugbeeinflussung signalling system, rather than upgrading the system to the more modern Linienzugbeeinflussung (LZB) system, as used on the Munich S-Bahn to achieve a throughput of 30 trains per hour in each direction in the Munich core city tunnel.
A further cause of delays is that many of the S-Bahn lines share track with freight trains, regional trains and inter-city trains. Longer distance passenger trains take priority over the S-Bahn, which frequently has to stand for up to 10 minutes to allow the other service to overtake. Mixed services are particularly found along the S6, S7, S8 and S9 routes. The operators recognise the need to separate S-Bahn services from other services along these routes. The first stage towards this was originally scheduled to start in 2007, doubling the number of tracks from two to four on the S6 line between Westbahnhof and Bad Vilbel, but in October 2011 Deutsche Bahn stated that it expected work to start in 2014 and the extra tracks to go into service in 2018.
- "Hintergrund: 380-Millionen-Investition". Frankfurter Neue Presse. Frankfurter Societäts-Medien GmbH. Retrieved 24 November 2011.
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