U, U11 and U2 Stock
The first standard Vienna metro train was delivered in 1972 by Simmering-Graz-Pauker (SGP), six further prototypes were delivered the following year. These were extensively tested on a new test track near Heiligenstadt. The technical specifications were to some degree based on the trains designed for Munich, with some minor adaptations; the design, however, was radically different and won a number of awards. These trains, called U stock, are coupled in units of two that cannot be operated alone. Aluminium was used for the car body, which reduced the weight by about 50% compared to a steel body. Until 1982, 136 units (272 cars) of this stock were built.
These trains are equipped with automatic train operation of the LZB type (Linienzugsbeeinflussung). Signal aspect and speed are transmitted directly to the train using antenna loops installed between the rails. The "driver" is only responsible for operating the doors, starting the train, and intervening in case of emergency.
U stock (WVB)
U11 stock (WVB)
N1/n2 and U stock (WVB)
When additional trains were needed for the opening of line U3 in 1991, nine prototypes of U1 stock were tested from 1987 onwards. The final design, numbered as U11 stock, is similar in outward apperance to U stock; however, the new cars have water-cooled AC motors with recuperative brakes, self-steering bogies to reduce wear in curves and a completely redesigned ventilation system. As of December 1999, there are 117 units (234 cars) of U1/U11 stock in service on the Vienna metro.
From 1991 onwards, U stock was slightly modified to meet new safety regulations; at the same time the plastic seats were replaced with the fire-proof cloth ones used in U11 stock.
Currently, trains from the second batch of U stock (numbers 2063/3063-2136/3136) are being fitted with new AC motors and new electronic equipment as part of a refurbishment programme. The refurbished units are referred to as U2 stock and are stationed at Erdberg depot for use on line U3.
The standard formation consists of 3 units or 6 cars; only generic trains are formed: U-U-U or U11-U11-U11. Only U2 stock units are often coupled with U stock. After 8 pm and on Sundays 4-car trains are used: U-U or U11-U11.