Operations
The R4 operates every hour between and , using the western end of the Simplon line. The R4 makes all local stops between and . The R4 is paired with the R3 between and Bex, providing half-hourly service. Both the R3 and R4 provide limited service beyond Bex to . On weekdays, a section of the R4 operates between Le Day and .History
The "first" S4 was one of the six original lines of the RER Vaud, then called the Vaud Express Network (, REV), when that system was established in December 2004. It ran hourly between Morges and Palézieux. SBB extended the S4 west from Morges to Allaman with the December 2011 timetable change, making local stops. Rush-hour service to Romont began on 10 December 2017. In December 2021, SBB increased the number of rush-hour round-trips between Allaman and Romont from three to six. The RER Vaud lines were substantially reorganized for the December 2022 timetable change. The "new" S4 was a combination of the former S2 and S22, making local stops on the Simplon line between Vallorbe and Lausanne, and limited stops between Lausanne and Aigle, with limited service from Aigle to St-Maurice. On 10 December 2023, all RER Vaud lines were renamed as "R" and a number, instead of "S". In December 2024, the R4 was extended from to , the service from Bex to St-Maurice was taken over by the RE33 service.References
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