| S21 | |
| Type: | S-Bahn |
| System: | Zürich S-Bahn |
| Locale: | Zürich, Switzerland |
| Stations: | 5 |
| Operator: | Zürcher Verkehrsverbund (ZVV) |
| Map Name: | map_name |
| Map State: | hide |
The S21 is a regional railway service of the Zürich S-Bahn of the Zürcher Verkehrsverbund (ZVV). The service operates at peak hours between and over the Wettingen–Effretikon railway, supplementing the regular service, which continues west to .
At, trains of the S21 service usually depart from ground-level track (German: Gleis) 18.
The service operates on weekdays during peak hours; there are a total of eight trains in each direction per day. Inbound trains in the morning and outbound trains in the evening bypass . Trains usually depart from (or arrive at) one of the surface platforms of . The S21 calls at the following stations:[1]
The S21 designation was previously used for service from Zürich to over the Thalwil–Arth-Goldau railway; this is now provided by the . The current S21 began running with the December 2015 timetable change.[2]
most services are operated by Re 450 class locomotives pushing or pulling double-deck passenger carriages.[3]