last delivered in 2010. In order to increase the number of low-floor trams in service, 23 trams from the otherwise high-floor Tram 2000 fleet were rebuilt between 2001 and 2005 with the addition of a low-floor centre section. From the 1950s onwards, the Glattal region to the north of Zürich experienced a rapid boom as population and industry spilled over from nearby Zürich, partly driven by the presence of Zürich Airport. Whilst the airport is served by the city's S-Bahn rail network, the economic growth and resulting congestion led to a need for a finer-grained form of public transport. The responsible transport authority (the Verkehrsbetriebe Glattal or VBG) responded by constructing a new light rail system, the Glattalbahn. This was built to be compatible with Zürich's tram network, with which it connects at several points on the city boundary. The system opened in stages between 2006 and 2010. The VBG contracted the VBZ to operate the network, and several tram routes now operate across both networks. The arrival of new trams between 2001 and 2010 led to the departure of older vehicles. The Karpfen last ran in regular service in 2006, and the Mirage in 2010. Many members of both classes have been transferred to Vinnytsia in Ukraine. More extensions and Mirages make a comeback Tram Zürich West, an extension from Escher-Wyss-Platz to Bahnhof Altstetten Nord, in the city of Zürich, opened in December 2011. The resulting reorganisation of routes included a new route 17 from Hauptbahnhof to Werdhölzli via Escher-Wyss-Platz, and the diversion of route 4, which had previously served Werdhölzli, to Altstetten. In 2017, route 8 was extended from Hardplatz to Hardturm, via a new track over Hardbrücke, the first tram line to cross the main railway line through Zürich (project Tram Hardbrücke). An extension of the tracks from Hardbrücke to Bucheggplatz and Milchbuck (project Rosengartentram und Rosengartentunnel), along with the opening of two new tram routes, was rejected by a referendum in 2020, however. This project would have also included a loop tunnel for the cars between Hardbrücke and Bucheggplatz. In September 2019, city route 2 was extended from Farbhof to Geissweid (Schlieren), a distance of with seven stops. The new route operates over the first section of the so-called Limmatalbahn, not to be confused with the now expired Limmattal tramway, and replaces trolleybus route 31 over that section (line 31 now terminates at Hermetschloo station). The