The long Hirschengraben Tunnel was built for the S-Bahn from the Hauptbahnhof to Zürich Stadelhofen. This new line continued through the Zürichberg Tunnel to Stettbach, with connections to the existing lines to Dietlikon and Dübendorf. In the Hauptbahnhof, two underground stations were constructed. For the S-Bahn, a four-track station with the working title Museumstrasse was built, and the Sihltal Zürich Uetliberg Bahn was extended to the SZU station, which had once been intended for the never-realized U-Bahn.