The metro-project was approved in 1970 and dropped in 1973 because the people
of Zurich decided against that project. By that time they'd already build a
tunnel next to the Milchbuck-motorway with three stations and a section near Hbf.
under an underground shopping mall with the Hbf. underground-station.
The Milchbuck-section was later used for the so called Schwamendingen-tram. The trams had to change from right to left operation in the tunnel because they have only doors on the right side and the stations have only single-platforms. So, the ramps for this tunnel are single-track-ramps one after another to avoid track-crossings at grade. The tunnel was opened in the Mid 80s and the stations have names different from those original planned. They had to develop a new concrete track bed in order to have enough space for a tramway with overhead-wire. The original design for the metro was third rail conduction.
The Hauptbahnhof-section was later used for the Sihltal-Uetlibergbahn. It is now part of the S-Bahn-network and uses two or three stations to reach the Hauptbahnhof without any level crossings. It was also opened in the late 80s.
Plans were for one line running from west to northeast and branching of three times in the east.
Stations from west to east:
From here one branch along the Milchbuck-tunnel with stations:
Hirschen Schwamendingen, probably further into Schwamendingen-area
The other branch towards north:
From here two branches with just a single station, one to Flughafen and one to Kloten
The streets which are probably planned to put the metro in are from north to south:
Leonhardstraße, at the ETH (university) truning sharp left
following the Sihltalbahn until Stauffacherplatz