in 2008 and 2010. In 2011 the city tram network was extended by the opening of the Zürich West project. Operations Trams Trams make an important contribution to public transport in the city, with the tram network serving most city neighbourhoods, and are the backbone of public transport within the city. Most of the tram routes run from city periphery to city periphery via the city centre. The VBZ owns the tram infrastructure within the city, and operates trams both over its own infrastructure and over the infrastructure of the Stadtbahn Glattal, a light rail system situated to the north of the city and owned by the Verkehrsbetriebe Glattal (VBG). Whilst some of the routes operated over the Stadtbahn Glattal are branded as VBG routes, all such services are actually operated by the VBZ under contract to the VBG. The joint tram network of the VBZ and VBG comprises 15 separate routes. The network operates on meter gauge track, electrified using overhead line at 600 V DC. The VBZ infrastructure is largely street based, with varying degrees of segregation from other street traffic but little use of dedicated rights of way for the trams with the notable exception of a tram tunnel in north-east Zürich that was originally built for an abortive metro system, and modified for tram usage. By contrast, on VBG infrastructure, VBZ trams operate on long stretches of dedicated track. The independent Forchbahn (FB) railway uses VBZ trackwork to reach the centre of Zürich from the eastern edge of the city. The FB trains operate largely in the street for this section of their route, sharing track with VBZ tram routes, but are categorised as part of the city's S-Bahn railway network rather than as part of the tram network. Two membership associations, the Tram-Museum Zürich and the Aktion Pro Sächsitram, also use VBZ tracks to operate occasional heritage tram services. The VBZ owns 313 tram vehicles, which between them cover over 16 million vehicle-kilometres per year. Of these, 88 are modern low-floor Bombardier Cobra trams delivered between 2001 and 2010. All the remaining trams in regular passenger service are of the Tram 2000 design, of which 201 vehicles were delivered between 1976 and 1992. Whilst the Tram 2000 is a high-floor design, 23 trams have been rebuilt with the addition of a low-floor centre section. Unlike the five-section Cobras, which normally only operate singly, the Tram