S4 (St. Gallen S-Bahn)

The S4 operates hourly between and via . The service is operated by Stadler Rail Flirt/Flirt-3 EMUs of Südostbahn (SOB). The S4 operates with the S6, S17 and IR Voralpen-Express between Rapperswil and , combining for four trains per hour and direction. The S4 does not call at intermediate stations and . The S4 and the S2 combine for half-hourly service between and . Service between St. Gallen and St. Margrethen is more frequent due to the additional S5, which runs hourly. Between Wattwil and Uznach, the S4 combines with the IR Voralpen-Express for a half-hourly service, although only the S4 stops at Kaltbrunn. == Route ==

The service links the Alpine Rhine Valley and the city of St. Gallen with the Obersee region, via Herisau, the capital of the canton of Appenzell Ausserrhoden, and the Toggenburg Valley. – – – – – – – – – • Rapperswil • Uznach • • Wattwil • • (stops only on request) • (stops only on request) • • (stops only on request) • Herisau • • St. Gallen • • • • • Rorschach • • • St. Margrethen • • • • Altstätten SG • • • • Buchs SG • • Sargans == History ==

Prior to the December 2013 timetable change, the S4 operated between St. Gallen and . Local service between Uznach and was handled by an hourly regional service that ran between and . Service southeast of St. Gallen toward Sargans was handled by various local services, but only the '''' operated over the whole route. Südostbahn introduced the new S4 on 15 December 2013 as a circle line (), which was sometimes referred to as the 'Alpstein round trip' (Alpsteinrundfahrt). Until 9 December 2023, the service operated hourly in both a clockwise and counter-clockwise direction. A full journey around the circle took approximately three hours. In , which lies to the west of the junction between the Uznach–Wattwil and Rapperswil–Ziegelbrücke lines, the trains reversed their direction of travel before continuing on the circle route. With the 10 December 2023 timetable change, the circular operation ended. The S4's new termini became and Sargans, respectively, and the new S17 began running between Rapperswil and Sargans via . However, the trainsets operating as S4 and S17 services continue as the respective other line from Sargans, so that passengers can still take the circular route around Alpstein without changing trains in Sargans; a change of trains is nonetheless required in either Uznach or Rapperswil. Rerouting of the S4 and introduction of the new S17 service were made possible through the expansion to dual track between and (constructed between 2021 and 2023) on the Rapperswil–Ziegelbrücke railway line. == References ==