On 23 February 2003 the Swiss Federal Railways' board of directors decided to give the 447 million CHF contract for building 35 double decker trains to Siemens Transportation Systems. This decision came as a surprise since Siemens had never built double decker EMUs before, except for an experimental train built in a consortium with DWA Görlitz that never entered into service. To fulfill the domestic content requirement in the contact, Siemens reached an agreement with Stadler Rail to perform some of the assembling and the commissioning in their factory in Altenrhein, Switzerland. The trains were originally intended to enter service in December 2005, but the date could not be kept. Nevertheless, the first trainset was presented to the public on 2 December 2005 at Zürich Hauptbahnhof. Until May of the next year, the RABe 514 were thoroughly tested and then entered into regular passenger service on the S14 line. In March 2006 the Swiss Federal Railways exercised their purchase option for another 25 units. Because of the delayed delivery of the first trainsets, Siemens agreed to build an additional train instead of paying a penalty. Delivery of all 61 trains was completed in July 2009.
The DTZ trains are the second generation double decker trains used on the Zürich S-Bahn. Compared to the Re 450, the first generation trains, the RABe 514 feature a low-level entrance for level boarding, air conditioning and vacuum toilets. The four-car multiple unit consists of two powered end cars with two unpowered cars between them. Both bogies in an end car are driven by induction motors with a power output of 400 kW per axle providing a total of 3200 kW for the trainset. Since there was not enough space for a 15 kV power line through the train, both end cars draw their power from a separate pantograph. An automatic coupling system allows for up to four trainset to be connected together for additional capacity, however in practice the maximum is three connected trains due to the limited platform lengths of 300 m at the train stations.
Interior
The double decker trains provide 74 seats in first class, 304 seats in second class as well room for about 600 people standing. The first class seats are equipped with normal 230 V power outlets for charging notebooks and other devices.
Service
The RABe 514 are used on lines previously served by Re 450. The thereby freed up Re 450 trains were then used to replace the old single deck trains RABDe 510 and RBe 540 from the 1960s. The first line served by the new Siemens trains was the S14. Starting in December 2006 the S7 line was also equipped with the new trains. However all newly delivered trains were first put on the S14 line because that line is better suited for testing due to its short length and lower importance than other lines. After the S7 line got all of its required 15 trainsets, the next trains were intended to go to the S5 line, but that plan was abandoned in favor of the S15. With delivery of the second batch, the S8 line was equipped as well. S16 also use DTZ trains. The original plan to couple first and second generation trains together to provide level-boarding on more lines could not be implemented due to software problems when connecting the two train generations.
