The S-Bahn operates over 603 km (375 mi) of route in the states of Rhineland-Palatinate and Baden-Württemberg, and in small sections in Saarland and Hesse.

S-Bahn trains operate about 7.5 million kilometres per year, with 113 stations served by class 425 electric multiple units.

An extra bridge was built over the Rhine between Mannheim and Ludwigshafen, urgently required to increase capacity, a by-pass of Schifferstadt for long-distance traffic and Ludwigshafen-Mitte S-Bahn station in Berliner Platz.

The upgrade of the Mannheim–Kaiserslautern line to Homburg was carried out as an urgent project in preparation for the 2006 FIFA World Cup.

[2] To the extent that they did not already meet this requirement, all stations on the Heidelberg–Karlsruhe route were extended to 140 m (150 yd) of platform length during the first expansion phase in order to enable S-Bahn trains to stop in double sets.

[4] At six stations, the platforms were extended to 210 m (230 yd) in order to be able to use S-Bahn trains in triple sets due to the expected traffic volume.

However, the schedule laid down in the Realisierungsprogramm Rhein-Neckar-Takt 2010 (implementation program for the 2010 Rhine-Neckar clock-face timetable), which provided for further expansion to Homburg, Bruchsal, Karlsruhe, Eppingen, Darmstadt and Worms,[6] between 2008 and 2010, was rejected again in 2006.

The reasons for this were the reduction of funds made available under the federal Rail Regionalisation Act (Regionalisierungsgesetz) in accordance with the so-called "Koch-Steinbrück paper" as well as the need to finance infrastructure measures required for capacity increases in the north of the region, in particular the Frankfurt–Mannheim high-speed railway.

[7] In August 2002, a "standardised assessment" for the electrification of all three routes to Aglasterhausen, Bad Friedrichshall-Jagstfeld and Eppingen showed a benefit-cost ratio of 3.7.

The district administrator and former director of the Rhine-Neckar Metropolitan Region, Stefan Dallinger, stated that he was not aware of any project with such a good result.

[8] The modernisation of 78 kilometres of line covered 110 km (68 mi) of track[7] and included the installation of about 1180 sets of overhead masts.

[10] The second stage of expansion also included the integration of the Bruhrain Railway from Germersheim via Graben-Neudorf to Bruchsal into the S-Bahn network.

This route was added to the S-Bahn network at the 2011/2012 timetable change on 11 December 2011 and is used by an extension of the S 4, but which is designated as the S 33 to avoid confusion with a line of the Karlsruhe Stadtbahn.

Early operations of S-Bahn trains using adapted class 425 stock were implemented on the Mainz–Worms–Frankenthal–Ludwigshafen am Rhein–Mannheim(–Weinheim–Bensheim) Regionalbahn route from the beginning of 2006.

Construction began in 2012 and 2013 at Mainz Römisches Theater, Ludwigshafen-Oggersheim, Mettenheim and Bodenheim,[13] and work at another ten stations was completed by June 2016.

The planned establishment of stations in Roxheim and Worms Süd[14] was abandoned as the responsible municipalities were unwilling to fund them.

In the northern part of the line, the Neulußheim and Hockenheim stations already had the required platform lengths and heights, so only lifts had to be retrofitted.

Two compact stations were built in Mannheim-Rheinau and Mannheim-Neckarau, which allow a quick and barrier-free change to the trams and buses of the RNV.

[17] In contrast, the case for building Neckarau station would be "examined in terms of the costs and benefits of the whole line",[18] so it may not in fact be built.

[19] Construction work at the Schwetzingen-Hirschacker station began on 29 March 2021 and was completed in time for the timetable change in December 2022.

[20] On the Hessian side, the Riedbahn between Mannheim and Groß-Rohrheim was also integrated into the network of the Rhine Neckar S-Bahn as line S 9.

The line was originally planned to run only as far as Biblis, but the Bergstraße (district) was able to have it extended with the fare boundary between the Verkehrsverbund Rhein-Neckar (VRN) and the Rhein-Main-Verkehrsverbund (RMV) moved to Groß-Rohrheim.

[21] At the end of January 2016, the state of Hesse concluded an implementation and financial agreement with DB Station&Service under which the state of Hesse invested €5 million in the upgrade of five Hessian stations, Lampertheim, Bürstadt, Bobstadt, Biblis and Groß Rohrheim.

In addition, affected municipalities participated through the Zweckverband Verkehrsverbund Rhein-Neckar and providied €8.2 m, while the federal government provided €11 m. Construction began on 7 July 2016 with a groundbreaking ceremony at Biblis station.

Since track 12 was already operating while the passenger underpass at the northern end of the platform had not been completed, a temporary solution had to be put in place by July 2017.

[35] Due to the high utilisation on the Rhine Valley line on the Bruchsal–Heidelberg section it is planned to extend the platforms from 140 to 210 metres, so that longer trains can run.

The connections and cycle times of the S-Bahn must therefore be based on the few remaining train paths on the routes, especially since the longed-for relief that would be provided by the planned Frankfurt–Mannheim high-speed railway has receded into the future.

Instead, the operating concept prescribed by the tender stipulates that the main line will be connected from Mainz via Worms and Mannheim to Bensheim, which was implemented in 2018.

An integrated system to bridge gaps should allow people with reduced mobility to make a stepless entry and exit to 76 cm-high platforms without assistance.

The exterior finish of the sets will not be Deutsche Bahn red, but light gray with dark grey sections in the door areas and a large S-Bahn logo.