The S20 is a railway service of RER Fribourg that provides hourly service between and , in the Swiss cantons of Neuchâtel and Fribourg, respectively. Transports publics Fribourgeois operates the service.
The S20 runs hourly between and . It uses the western end of the BernâÂÂNeuchâtel line and the entirety of the FribourgâÂÂIns line. It is paired with the S21, providing half-hourly service between Neuchâtel and Fribourg/Freiburg.
RER Fribourg introduced the S20 designation on 14 December 2014 for an hourly service between and Neuchâtel. In December 2017, the S21, previously a rush-hour service between Fribourg and , was re-routed to run between Fribourg and Ins and rescheduled for hourly service on weekdays, increasing the service level between Fribourg and Ins to half-hourly on weekdays. With the December 2021 timetable change, both the S20 and S21 were extended south from Fribourg to Romont, replacing the S40. The S21 began running on weekends with this change, while the S20 operated between Fribourg and Romont on weekdays only. In December 2024, the service between Fribourg and Romont was transferred to the S40/S41 lines.