S4 (RER Vaud)
The S4 is a railway service of RER Vaud that provides hourly service between and in the Swiss canton of Vaud. On weekdays, rush-hour services continue from Palézieux to , in Fribourg. Swiss Federal Railways, the national railway company of Switzerland, operates the service. Operations. The S4 operates every hour between and , using the Lausanne–Geneva line between Allaman and and the Lausanne–Bern line between Lausanne and , via . The S4 runs as an express between and Lausanne, stopping only at . It is paired with the S3 between Allaman and Lausanne, providing half-hourly service between the  two cities. Between Lausanne and Palézieux it operates with the S6, S9, and InterRegio 15; combined there is service over the line roughly every 15 minutes. Northeast of Palézieux, the S4 operates to Romont during weekday rush-hour only. It is the only stopping service for and . History. The 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.