The Limmattal light rail line is a new metre gaugelight rail line that is proposed, under construction and partially completed on an alignment running through the Limmat Valley, in the Swiss cantons of Aargau and Zürich to the west of the city of Zürich. The new line will, when fully completed, be long, will serve 27 stops, and will operate from Zürich Altstetten to Killwangen via Farbhof, Schlieren, Urdorf, Dietikon and Spreitenbach. The Limmat Valley is a major transport corridor. Its first railway was the first line in Switzerland, the so-called Spanisch-Brötli-Bahn that opened in 1847, and that line now carries long distance passenger trains, freight trains and suburban trains of the Zürich S-Bahn. However the stations of the S-Bahn are well separated, with only five stations in the distance to be covered by the Limmattal line. The Limmattal tramway provided more local transport from 1900, but closed in stages between 1928 and 1955, being replaced by buses. The roads of the Limmat Valley are now at capacity, leading to delays to both bus and car traffic. It estimated that traffic will continue to grow, with 113,000 extra journeys a day by 2030. It is against this background that the Limmattal light rail line was proposed as a solution. Planning began in 2000, and by 2007 the line was included in the cantonal plans of Aargau and Zürich. In 2010, the Limmattalbahn AG company was founded by the cantons to plan and implement the infrastructure for the line. A referendum, held in November 2015, approved the construction of the line, and it was announced in May 2016 that the line would be operated by BDWM Transport, who also operate the Bremgarten–Dietikon line. Construction commenced in August 2017, and phase 1 between Farbhof and Schlieren opened in September 2019. A further referendum called by opponents in the canton of Zürich in an attempt to have phase 2 cancelled was defeated, and the line is expected to be fully opened throughout in 2022. When fully open, light rail trains will run every 15 minutes between Zürich-Altstetten and Killwangen-Spreitenbach stations, with the ability to later increase the frequency to every 7.5 minutes. The line will be double-track throughout, and over 90% segregated from road traffic. The stretch of the line between Farbhof and Schlieren is already used by an extension of Zürich tram route 2, running every 7.5 minutes and replacing the existing Zürich trolleybus route 31 over that stretch. This section will continue to be served by both services once the whole line is opened. The Limmattal and Bremgarten–Dietikon lines will also share a short section of track on the existing alignment of the latter in the centre of Dietikon. From Farbhof to Schlieren the line is electrified at 600 VDC for compatibility with the Zürich tram network, and the section of phase 2 between Altstetten and Farbhof will also be electrified at this voltage. The rest of the line will be electrified at 1200 V DC, which is also used by the Bremgarten–Dietikon line. A joint order, with Baselland Transport, has been placed with Stadler for the supply of new light rail vehicles to operate the service from Altstetten to Killwangen. The Limmattal portion of this order is for eight long and wide double-ended Citylink vehicles, with an option for up to eight more, for which a depot is to be constructed between Dietikon and Spreitenbach. The extension of Zürich tram line 2 is operated by the existing single-ended Zürich tram fleet, for which a turning loop has been provided at Schlieren.
