the Hauptbahnhof was intended to ease the pressure on the Hauptbahnhof. On 20 May 1973 this proposal was rejected in a referendum, with the "no" vote as high as in the previous referendum. At the referendum, little opposition had been expressed against the proposed S-Bahn lines. Coordination and construction of the S-Bahn Rail is a major element in Zürich's public transport system, and its upgrade required close collaboration between the canton of Zürich and Swiss Federal Railways (SBB CFF FFS), the owner of most of the railways. The SBB CFF FFS had insufficient resources for a substantial upgrade of commuter services. On the other hand, the canton of Zürich could not fund an alternative transport network. The first step towards cooperation came in 1978 with the establishment of a Transport Fund providing CHF 40 million annually for urban transport. The routes of today's S-Bahn were established in a debate in the cantonal Council on 19 June 1978. Alternative "eastern" and "western" options were discussed. Under the western option the northern end of the central tunnel from the Hauptbahnhof would have connected with Oerlikon, while in the eastern option it would have tunneled under the Zürichberg and ended near Dietlikon. The cantonal Council chose the eastern option by 85 votes to 36. At a referendum on 29 November 1981, Zürich's voters approved by a two-thirds majority a loan of CHF 520 million for the construction of the core of the S-Bahn. The following changes were made: The construction of the Hirschengraben tunnel between the Hauptbahnhof and Stadelhofen. Four new platforms were built under the existing Hauptbahnhof, along with connections to the existing western lines. The Letten Tunnel and station were closed. The construction of the Zürichberg Tunnel, which connected Stadelhofen to lines to the northeast, as well as having a new station at Stettbach. The extension of the Sihltal Zürich Uetliberg Bahn lines from Selnau to the Hauptbahnhof, with the Selnau terminus closed and replaced with an underground through station. The opening of Hardbrücke railway station in 1982, between the Hauptbahnhof and Altstetten to the west. The redevelopment of Stadelhofen station, with an architecture award-winning design by Santiago Calatrava. Opening and expansion On 27 May 1990, the S-Bahn was brought into operation and the Zürcher Verkehrsverbund (Zurich Transport Network) began operations. For the first time, one could travel on trains, buses and trams with just one ticket. Despite "teething problems", passenger