The 2.1 km (1.3 mi) 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.[5] In the Hauptbahnhof, two underground stations were constructed.