Vienna Underground Tram

The Vienna Underground Tram (German: U-Straßenbahn Wien) or Vienna premetro refers to tunneled sections of the Vienna tram network constructed during the 1960s and 1970s.

These sections allowed trams to bypass congested surface traffic and were designed with the possibility of future conversion to full metro lines in mind. Some sections have the same function to bypass other traffic, but were not designed for conversion to U-bahn service. The tunnels, along with one viaduct, are maintained and operated by Wiener Linien, the main public transport operator in Vienna.

Two of the total five grade-separated sections are several kilometres long. One major section, the Zweierlinie, opened in 1966, was converted into the Vienna U-Bahn system and opened as such in 1980. Additionally, the Gürtel tunnel is also used by the Wiener Lokalbahnen (WLB), which operates a regional tram-train service. Located along the southern Gürtel (belt road), this section opened on 11 January 1969 and remains in operation as an underground tramway tunnel.

The tunnel sections are known in German as Unterpflasterstraßenbahn (literally "under-pavement tramway") or Untergrundstraßenbahn ("underground tramway") and are sometimes abbreviated as UStrab.