S21 (ZVV)

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 Zürich HB, trains of the S21 service usually depart from ground-level track (Gleis) 18.

Route
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 Zürich HB. The S21 calls at the following stations:



History
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.

Rolling stock
most services are operated by Re 450 class locomotives pushing or pulling double-deck passenger carriages.