The Zurich–Lucerne line is a major railway line in Switzerland, connecting the cities of Zurich and Lucerne via Thalwil and Zug. Between Zurich and Thalwil, the line shares its tracks with the Lake Zurich left-bank line, although many through trains on this stretch now use the Zimmerberg Base Tunnel rather than the lakeside line. As far as Zug, the line also carries through trains from Zurich to the Gotthard line.
The first section of the line between Lucerne and Zug was as part of a line from Zurich via Affoltern am Albis. The Swiss East–West Railway (German: Schweizerische Ostwestbahn, OWB) gained the concession for this line as part of a plan to build a line to compete with the network of the Swiss Central Railway (German: Schweizerische Centralbahn, SCB) in central Switzerland connecting Basel, Olten, Bern, Brugg, Lucerne and Biel, on which construction commenced in 1857. The OWB began construction without raising sufficient finance to guarantee its completion. It opened a line on the western side of Lake Biel, which is now part of the Jura foot line in 1860, but then went bankrupt. The concession for the section from Lucerne to Zurich via Affoltern am Albis was bought out of the bankrupt estate by the Swiss Northeast Railway (German: Schweizerische Nordostbahn, NOB) and established as a subsidiary, the Zurich–Zug–Lucerne Railway (German: Zürich–Zug–Luzern-Bahn, ZZL). Construction of the line was completed in 1864 and shortly later it was connected to Schweizerische Centralbahn's Olten–Lucerne line to Lucerne station, which had opened in 1856 on the edge of the lake, across the Reuss from the centre of the town; its site was close to the current station, which opened in 1896, but burnt down in 1971 and was subsequently rebuilt.
The Gotthard Tunnel was opened in 1882 with connections to Zurich and Lucerne via the ZZL at Rotkreuz. Planned direct connections to Lucerne from Immensee and to Zurich from Arth-Goldau via Thalwil and Zug—to be partly financed by the Swiss government—were postponed for financial reasons. On 1 January 1892, the ZZL was fully incorporated into the Nordostbahn to facilitate the construction of the line from Thalwil to Arth-Goldau. The section from Thalwil to Zug and Arth-Goldau opened on 1 June 1897, including the 3,359m long Albis Tunnel and the 1,985m long Zimmerberg Tunnel. The Nordostbahn was nationalised on 1 January 1902 and became part of the Swiss Federal Railways.
The first stage of the Zimmerberg Base Tunnel was completed in April 2003 as part of the first stage of Rail 2000, a project that upgraded many Swiss lines, completed in 2004. This tunnel is 9,478 m long (western tube)—including its exit to Thalwil—and includes a junction for its proposed extension to a future junction near Litti at the southern end of the Albis Tunnel. The completed tunnel is used by long-distance services and some suburban services of the Zürich S-Bahn, releasing the surface line for intensive use by the S-Bahn.
The line is standard gauge and is electrified at 15 kV 16 2⁄3 Hz AC supplied by overhead line. It is largely double-tracked, but has single track sections through the Zimmerberg and Albis tunnels, from Freuderberg to Rotkreuz, and from Rotsee to Fiumühle. Between Zurich and Thalwil, the line shares its tracks with the Lake Zurich left-bank line, although many through trains on this stretch now use the first stage of the Zimmerberg Base Tunnel rather than the lakeside line.
Between Zurich and Zug, the line carries through trains from Zurich to the Gotthard line, include EC trains to Milan, and ICN and IR trains to various points in the canton of Ticino. IR trains operate over the whole length of the line between Zurich and Lucerne every 30 minutes, stopping at Thalwil and Zug, with some stopping at Baar and Rotkreuz as well.
The section from Zurich to Zug is used by trains of the Zürich S-Bahn The section from Lucerne to Zug is used by trains of the Luzern S-Bahn and the Stadtbahn Zug.
The proposed second stage of Zimmerberg Base Tunnel, which would be about 10 kilometres (6.2 mi) long, would bypass a hilly section of single track, including the existing Zimmerberg and Albis tunnels, and provide an expansion of capacity to serve the Gotthard Base Tunnel, which is expected to open about 2016. However no funding has yet been committed the building of this second stage.