The R4 operates every hour between Le Brassus and Aigle, using the western end of the Simplon line.

[5] SBB extended the S4 west from Morges to Allaman with the December 2011 timetable change, making local stops.

[7] In December 2021, SBB increased the number of rush-hour round-trips between Allaman and Romont from three to six.

[8] 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.