S3_(St._Gallen_S-Bahn)
The S3 was a railway service of the St. Gallen S-Bahn that provided hourly service between St. Gallen and St. Margrethen, in the Swiss canton of St. Gallen. THURBO, a joint venture of Swiss Federal Railways and the canton of Thurgau, operated the service. It was replaced by a lengthened S5 as part of the December 2021 timetable change.