low-floor trams, whilst at least every other journey on lines 2, 3, 4, 7, 9, 11, 13 and 14 are provided by such vehicles. Most, but not all, tram stops are configured to allow passengers in wheelchairs to board low-floor trams. Of the three routes that operate in part over Glattalbahn tracks, routes 10 and 12 are operated by the VBZ on behalf of the Verkehrsbetriebe Glattal (VBG), normally using tramcars in the VBG's own predominantly white colour scheme, whilst route 11 is operated by the VBZ on its own behalf, normally using vehicles in its own livery. In December 2022, the Limmattalbahn opened services between Zürich Altstetten and Killwangen-Spreitenbach (Aargau). It was designated line 20 and is operated by AVA using double-ended (i.e. with two driver's cabs) Stadler Citylink vehicles. The independent Forchbahn (FB) railway uses VBZ trackwork to reach their city centre terminus, at Bahnhof Stadelhofen, from the eastern edge of the city, at Rehalp. The FB trains operate largely in the street for this section of their route, sharing track with VBZ tram routes, but are categorised as route S18 of the city's S-Bahn railway network rather than as part of the tram network. Beyond Rehalp the trains use the FB's own segregated tracks to reach their outer terminus at Esslingen. On the last weekend of each month, the Zürich Tram Museum operates tram route 21 (Museumslinie) from the city centre to the museum at Burgwies (up to Rehalp at Saturdays), using their own heritage rolling stock. Infrastructure Zürich's tram network is built to metre gauge ( gauge). There are of track, equating to a network length of and a total route length of . The tracks are electrified using overhead line at 600 V DC, utilising a supply system shared with the city's trolleybus network. The VBZ infrastructure within Zürich is largely street based, with varying degrees of segregation from other street traffic and significant sections where trams run in unrestricted traffic lanes. In the city centre the tram tracks run through largely pedestrianised streets, and in one place in the suburbs the trams use a tunnel originally constructed for the never completed Zürich U-Bahn system. By contrast, on VBG infrastructure in the Stadtbahn Glattal, VBZ trams operate on long stretches of dedicated track. Many of Zürich's tram stops have been equipped with boarding platforms raised to match the floor height of the low floor trams,