hours. The nighttime S-Bahn and bus routes form a network, which is different from the daytime network. Most SN services run hourly. As of December 2022, the following nighttime S-Bahn services exist: Previous services The S1 formerly linked Zürich and Zug via Thalwil. It was renamed the S21 after the opening of the S1 line of the Lucerne-Zug network (Zug Stadtbahn and Lucerne S-Bahn) in 2004 to avoid confusion. It is discontinued and replaced with the part of the line S24. The former S11 was a rush hour service. It was subsumed into the S23 in December 2018 when the current S11 service opened. The former S12 operated between Brugg and Seuzach/Seen until December 2018. The former S21 was subsumed into the S24 after the opening of the Weinberg Tunnel in 2014. The S22 formerly linked Bülach with Singen (in Germany) via Schaffhausen. It has been replaced by the S9 and S24 services, respectively, in 2015. A line numbered S22 still ran between and until 2018, operated by THURBO, but this one is currently running as an unnumbered S-Bahn service of . The S31 used to run across the Seedamm, between Rapperswil and Pfäffikon SZ. The S43 ran between Rüti ZH and Wald ZH (near Rapperswil) and had only three stations and was in fact a limited service of S26. It has been replaced by a bus route. The S55 formerly linked Niederweningen and Oberglatt, as a short-working of the S5. It has now been replaced by the S15. The S3 formerly operated between Wetzikon and Aarau via Dietikon. However its western route is overtaken by the S11, it runs to Hardbrücke (or Bülach) instead. International services Two Zürich S-Bahn services cross the international border into Germany. Service S9 crosses German territory between Rafz and Schaffhausen (both in Switzerland), calling at the German stations of Lottstetten and Jestetten. These two stations are located entirely on German soil, but all the infrastructure belongs to SBB. Service S36 crosses the border at the end of its journey, in order to terminate at Waldshut station in Germany. Network map Future developments Further improvements are envisaged, including two additional tracks at Oerlikon railway station, a passing loop in Pfäffikon and adjustments at various stations. Further improvements in the corridor between the airport and Winterthur are being developed as part of the second stage of Rail 2000 for long-distance trains, which would require further adjustments