On 18 February 1916, the SBB decided that electrification of its network would be by the high-tension single-phase alternating current system that is still used on all routes. On 5 February 1923, the electrified Zug–Zürich railway was put into operation, the first electrified line to Zurich. By 1927 all routes from Zürich Hauptbahnhof had been electrified.