The Sihltal line was built by the Sihltalbahn company, which opened a line from Bahnhof Selnau to Sihlwald in 1892. Bahnhof Selnau was already in existence as the terminus of the Uetliberg line, and the two lines ran in parallel as far as Giesshübel station. Later in the same year, a freight branch was constructed linking Giesshübel station with Wiedikon station on the Lake Zürich left bank line of the Swiss Northeastern Railway. In 1897 the Sihltal line was extended to Sihlbrugg and a connection with the Thalwil–Arth-Goldau railway of the NOB. In 1924 the line was electrified using alternating current. In 1932 the management of the Sihltal line took over the management of the Uetliberg line, but the two companies remained in existence until 1973, when they were merged to form the SZU. In 1990, the two lines were extended from their previous joint terminus at Bahnhof Selnau to a terminus at Zürich Hbf station. This extension involved the construction of a new rail tunnel from Selnau to Hbf, and a new underground intermediate station adjacent to the former terminus. The underground platform and tracks used at Hbf were already in existence, having been built prior to 1973 for a U-Bahn scheme that was ultimately rejected by voters. Once the new extension had been opened, the former terminus at Selnau was redeveloped and little evidence of it is now visible. In 2006, the line was upgraded to allow a service every 10 minutes during peak periods. At the same time passenger services were withdrawn between Sihlwald and Sihlbrugg, although the track still exists and is used by occasional trains.
Operation
Route
The Sihltal line shares a common terminus with the Uetliberg line, utilising a dedicated underground island platform at Zürich Hauptbahnhof station. There is no rail connection to the rest of the station, but the platform is served by the same complex of pedestrian subways and subterranean shopping malls that link the station's other platforms. From Hauptbahnhof to Zürich Giesshübel station the two lines share a common twin-track line, initially in tunnel, partly running along and under the Sihl river. The current Selnau station is located in this under-river tunnel section. The two lines diverge at Giesshübel station, which is only served by trains on the Sihltal line. Also located here is a junction with the freight only branch to Zürich Wiedikon station on the Swiss Federal Railways' Lake Zürich left bank line. The next stop on the line is Zürich Saalsporthalle-Sihlcity station, which is adjacent to the large Sihlcityshopping mall, with direct access to the platforms from the mall. Further suburban stations follow at, and. Leaving the city of Zürich behind, the line closely follows the riverSihl, serving the stations of Sood-Oberleimbach, Adliswil and Sihlau in the municipality of Adliswil. At Adliswil, a short walk provides an interchange to the Adliswil-Felsenegg cable car, which rises to the summit of Felsenegg. Beyond Adliswil, the stations of Wildpark-Höfli, Langnau-Gattikon and Sihlwald are served, although many trains terminate at Langnau-Gattikon. Beyond Sihlwald, the line continues to a junction with the Swiss Federal Railways' Thalwil–Arth-Goldau railway at Sihlbrugg station, although this section of line does not carry a regular passenger service.
Services
The passenger services on the line now forms part of the Zürich S-Bahn, branded as the S4. Trains usually run every 20 minutes outside peak periods, and every 10 minutes during peak periods. Most trains terminate at Langnau-Gattikon station, with only one train per hour continuing to Sihlwald station. Standard Zürcher Verkehrsverbund zonal fare tariffs apply to the line. The night service of the S4 line, operating on weekends after midnight, runs between Zürich Hauptbahnhof and Langnau-Gattikon. The Zürcher Museums-Bahn operates occasional heritage railway services over the Sihltal line. On the last Sunday of every month from April to October, a steam service is operated from Zürich Wiedikon station to Sihlbrugg station. The ZMB preserves a selection of former Sihltal line rolling stock, including two early steam locomotives, and a railcar and a locomotive built for the original electrification.
Infrastructure
The Sihltal line is electrified using the standard Swiss mainline system of overhead lines at 15 kV 16.7 HzAC, whilst the Uetliberg line is electrified using overhead lines at 1200 VDC. In order to avoid conflict on the common section, the Uetliberg line uses an overhead line offset from the centre of the track, and its cars are equipped with specially designed pantographs to collect from this.
Rolling stock
Passenger services on the Sihltal line are operated with a mixture of single and double deck cars, sometimes with examples of both types in the same train. Traction is provided by electric locomotives, which operate their trains in push-pull mode with a driving car at the other end of the train. Six new multiple unit trains have been ordered to enter service in 2013, equipped for dual voltage operation so as to operate on both the Uetliberg and Sihltal lines.
