Zurich Underground Railway

The Zurich Underground Railway, or Zurich U-Bahn, was a project started in the 1970s to build a rapid transit network in the Swiss city of Zurich and several bordering municipalities. This project was itself preceded by several earlier plans dating from between 1864 and 1959. In April 1962, the "Tiefbahn" (lit. "deep rail") project was proposed, which would have included placing the Zürich trams underground in the city centre by building 21.15 km of underground lines, this was rejected in a referendum before any construction had been undertaken.

In the 1970s "U-Bahn" project, the first line would have led from Dietikon via Schlieren, Zürich HB, Oerlikon and Opfikon to Zurich Airport, including two short branch lines to Schwamendingen and Kloten. The two most important development axes of the agglomeration, Limmattal and Glattal, would have been joined onto the network. The line would have been 27.5 km long, 14.8 km of which would have been underground. At a later point in time the construction of two more lines was planned. In spite of initial optimism the project was rejected in a referendum by the voters in the canton of Zürich. Some parts of the lines, which had been built as preliminary work for the Underground that was never realised, are used today as the Milchbuck-Schwamendingen tram tunnel and as the terminus of the Sihltal Zürich Uetliberg Bahn.

Although the U-Bahn project was never completed, little opposition was expressed against the suburban rail lines that were proposed at the same time to complement the U-Bahn. These proposals eventually evolved into the current Zurich S-Bahn system, which uses several newly built tunnels to pass under both the city centre and adjoining hills.