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

S-Bahn- and U-Bahn lines in 1980

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

City-Tunnel Offenbach am Main

DBAG Class 423 approaching the elevated section of Frankfurt Westbahnhof

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 15/30/45/60 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 Mannheim–Frankfurt railway). 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 enabled all westbound S2 trains to travel all the way to Niedernhausen at 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 1:00 am and 4:30 am from Frankfurt Flughafen Regionalbahnhof to Konstablerwache (1:11 am/4:11 am from Konstablerwache to Frankfurt Flughafen Regionalbahnhof) and a 60-minute frequency between 12:49 am and 3:49 am from Wiesbaden Hbf and Hanau Hbf (1:46 am/3:46 am from Hanau Hbf to Wiesbaden Hbf)

Punctuality

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 2010 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.^[2]

Class 420

In the early years trains of the second and third series of electric locomotive class 420 in the color pure orange / Kieselgrau (contrary to original plans, the proposed paint carmine / kieselgrau was not used) were used in Frankfurt, although occasionally lent to 1990 due to lack of vehicles also from Munich blue white 420s were used, for example, the opening of the trunk line extension to Frankfurt South. The cars of the 2nd construction series were delivered completely to the S-Bahn Munich until the beginning of the 2000s. Due to the ever-increasing vehicle demand at that time were between 1980 and 2004 at irregular intervals all railcars of the third and fourth series and numerous cars of the fifth and sixth series from the S-Bahn Stuttgart delivered to Frankfurt.

In 2003 began the delivery of new class 423 railcars in Frankfurt, in parallel, in August 2003, the first ET 420 were retired. As of 2004, Frankfurt ET 420 no longer received any main examinations; this was only in 2007 with 420 271 started when it became clear that the delivery of the last railcar due to registration problems would have to be postponed indefinitely. All Frankfurt vehicles were also from 2007 to 2008 for three million euros, a modernization in the interior, which included light gray instead of striped partitions and new upholstery in the current design. At the same time, the already quite advanced phasing-out was severely curtailed and henceforth focused on the railcars of the third construction series in order to be able to take at least the oldest vehicles out of service. Two railcars received the test LED headlights, but these could not prevail in Frankfurt.

The rapid-transit railway Rhine Main had the first completely traffic-red vehicle park of the German course AG. This status was maintained until the end of 2003, when the S-Bahn Stuttgart handed over the orange-white and orange-pebble-gray units to Frankfurt. After just over a year, the S-Bahn were completely painted red by the z-position of the last orange-pebble-gray unit 420 376 early 2005. Until 2005, there was also the last pebble gray orange 420 (apart from 420 001) in Frankfurt, but this train was scrapped in the spring of 2005 in Trier-Ehrang.

In 2009, when the use of the class 420 at the S-Bahn Rhein-Ruhr was completed, the Essen depot delivered several ET 420 of the fifth and sixth series to Frankfurt. Although the Frankfurt plant made great efforts to align the railcars to the Frankfurt units (for example, most railcars were still redesigned in 2007), they were in such poor condition by the end of years of poor maintenance in North Rhine-Westphalia that From then on, they were usually taken out of service directly at the end of the investigation period.

In parallel, four Stuttgart trains of the seventh series were relocated to Frankfurt in July 2009. After the main inspection, three of them were initially deployed from mid-June, primarily on the S7 and the airport short-commuter (S8 / S9), later normal in mixed operation with older units on all ET 420 rides. In the spring of 2014, another train of the seventh series and four trains of the eighth series were relocated from Stuttgart to Frankfurt in order to absorb a shortage of vehicles resulting from deadlines in older 420s. This was also the only period in which the eighth series in Frankfurt was in use.

After an early deployment was already foreseeable at that time, no great efforts were made to adapt the car to the Frankfurt railcar - some of them were in the interior until the withdrawal with Stuttgarter advertising stickers.

The 65 remaining trains of the 420 series were still in operation until November 2014. Since the conversion of the S7 and some of the S1 (which had previously been performed by 420s since the autumn of 2013) to the new 430 series in May 2014 made numerous 420s redundant, the phasing out progressed sharply. Another reason for this was the expiry of the examination period of many vehicles, while at the same time main examinations were no longer worthwhile due to the manageable remaining service life.

In the last months of operation, trains of the 420 series were still in service on the S8 and S9 lines. In exceptional cases or in case of vehicle shortage a use of the series 420 in the entire network was possible, so that in very rare cases even to use z. B. came on the lines S5 and S6, which were converted in 2005 on the trains of the series 423.

The use of the 420 series in the network of the S-Bahn Rhein-Main ended in the night of November 3, 2014. A sale and other options - depending on the condition of the remaining units - according to the media checked, but has been since the end of the already most of the remaining railcars have been scrapped.

An official museum train was not kept by the S-Bahn Rhein-Main. However, a private association of railway friends in Gießen was able to take over the unit 420 298 on a permanent loan and undertake regular special services in the Frankfurt area with this railcar, which they also work up (initially in their last operational condition).

Class 423

While Stuttgart and Cologne were already supplied in 1999 with the successor series 423 and Munich between 2000 and 2004, the entire vehicle fleet exchanged, Frankfurt began in 2003 with the partial renewal, after 2002 for testing purposes, a few railcars of the S-Bahn Munich in the S-Bahn Rhine-Main were used.

Since October 2010, 100 series 423 multiple units have been running in Frankfurt am Main (third series: 301–305, 325–334, fourth / fifth series: 372–456). Since June 2006, the lines S1 (with the exception of single roundabouts), S4, S5 and S6 are complete with 423. Since the timetable change on December 9, 2006, the S2 line is also driving with the new railcars. The short commuter trains S8 and S9 from the main station to Frankfurt Airport are partially driven by 423. The line S3 is served since March 28, 2010 exclusively with 423. Initially, the new units were primarily used, which were only approved in early 2010.

In the second half of 2014, the trains of the 423 series were also on weekdays in regular operation on the entire route of the S8 / S9 on the way to accelerate the shutdown of the 420 series. Since the end of 2014, the new 430 series has been in use here.

A total of 100 units were ordered, which should be delivered by mid-2007. However, the last tranche of 13 units arrived in Frankfurt in 2010. The last class 423 railcar (423 456) was delivered at the end of October 2010. Short-term rental vehicles were also used by S-Bahn Stuttgart. The reason for the delay was the photocell problem.

Between 2013 and 2016, all of the Frankfurt 423 series railcars were modernized to take them to the level of the successor 430 series, after six years in service. This includes:

• the replacement of all LCD displays with larger LED displays
• a modernization of the interior with new seat cushion design
• the retrofitting of video surveillance cameras
• An adaptation of the passenger information through the installation of progress monitors and alignment of the announcement system to that of the ET430 (this step has not been completed to date [as of: August 2016])
• the refurbishment of the car bodies with new paint
• the retrofitting of microphone units for wheelchair users
• as well as the installation of new door closing signals.

The last point brought the modernized railcar and the RMV as the initiator of the modernization in the early days of severe criticism, as many passengers and train employees the new door signals (which also include a signal when the doors are open) as annoying, even annoying. The RMV referred to existing EU directives, which oblige the installation of such signals, admitted, however, that there had been a manufacturer-design error in the installation of the new signals, which could have increased the intensity of the beep unintentionally.

Class 430

The DB class 430 completely replaced the class 420 in 2014. In normal operation, only the class 423 and 430 are now in service. 91 430 series kits were supplied, which is 29 units more than needed for a mere replacement. The fleet was increased from 162 vehicles to 191 traction units. On 5 May 2014 took place on the S1 (Wiesbaden - Rödermark-Ober-Roden) and the amplifier courses of the S8 between Frankfurt Hbf and Kelsterbach the first passenger service of the class 430 in the Rhine-Main area. Almost three weeks later, on May 23, 2014, the S7 (Frankfurt Hbf - Riedstadt-Goddelau) was completely converted to the 430 series. At the end of October, the operations began on the "long" S8 and S9, since November 3, 2014, these lines have been completely reorganized.

The introduction of the new railcars was, as with the S-Bahn Stuttgart, accompanied by several problems:

• Following the conversion of the S7 in May 2014, a design error in the wheelchair ramp caused an accident in which a ramp slipped out of the train due to the lack of barbs during use, severely injuring a wheelchair user. Further use of the ramps was subsequently banned until further notice. However, as many platforms in the network are not high enough to disembark a wheelchair user without a ramp and handlers are not allowed to pick them up by hand, the DB Station & Service transport line had to be alerted to a mobile Ramp to bring the scene, which sometimes took several hours.
• In contrast to the 423 series, where only the ramp request buttons are directly behind the driver's cab used, all the request buttons were always active in the 430 series and were often groundless, resulting in each of the multi-purpose areas of the engine being challenged by the driver Train (depending on train length up to six pieces) on wheelchair users with exit request had to control, so that the trains quickly large delays collected and prematurely reversed, failed completely or were replaced on the way by older vehicles. This problem was particularly frequent after the S1 was converted to the new railcars, which drastically reduced line reliability in the early weeks. The fact that the wheelchair pushbuttons were now also attached to all doors and could easily be actuated accidentally further compounded the problem. After no other solutions led to success, starting in September 2014, all wheelchair push-buttons located in the door frame were removed.
• In the first winter of operations, there were other problems: As a result of inadequate heating of driver's cabs and particularly loud noise-related annoyance reports in enormous frequency in January 2015 so many train drivers were sick leave that the line S4 had to be set for several days.