First Stadler FLIRT for Zurich’s S4 enters commissioning phase

Stadler has completed the initial assembly of the first RBe 546 FLIRT electric multiple unit for Sihltal Zürich Uetliberg Bahn (SZU). The first train was placed on its bogies at Stadler's Bussnang factory in September 2026. It was subsequently transferred to Erlen on 29 September, where commissioning work includes activating, configuring and checking the interaction of onboard systems. Interior installation remains incomplete. Three of the 17 three-car FLIRT units ordered by SZU in September 2024 are currently under construction. Designated RBe 546, the new trains represent the largest rolling stock procurement in the Swiss operator's history. The 63-metre single-deck units will operate on the S4 Sihltalbahn between Zürich Hauptbahnhof and Sihlwald. Each train will accommodate 405 passengers, including 140 seated, and feature six low-floor entrances. Two units can operate in multiple, forming trains approximately 130 metres long. SZU opted for single-deck trains to replace its existing fleet of eight predominantly double-deck formations, some of which have been operating for more than 30 years. The new configuration is intended to shorten passenger boarding and alighting times on a suburban route characterised by short distances between stations. The procurement forms part of SZU's wider fleet and infrastructure modernisation programme, which also includes measures to increase service frequencies on its S4 and S10 networks. The first RBe 546 will undergo type testing and authorisation procedures during 2027, covering braking, traction, doors and passenger information systems. Commercial operation is scheduled to begin in May 2028, with all 17 trains expected to enter service by July 2029.