The Siemens-Düwag U2 is a type of light-rail tram vehicle (LRV). The cars were built by consortium of Siemens, Wegmann & Co. and Düwag. The U2 design was built on the Siemens U1 prototype tram built in 1965 (now stored at a Frankfurt tram museum).
Originally designed for and used by the Frankfurt U-Bahn, the model of car was adopted for light-rail use by transit systems in Edmonton, Calgary, and San Diego, during a period in which few purpose-built trams were being manufactured. All U2 cars were built between 1968 and 1990.
The U2's dimensions are 24.284 m (79 ft 8.1 in) by 2.650 m (8 ft 8.3 in) by 3.66 m (12 ft 0 in). In the US and Canada, usually up to five U2 cars are coupled to run as a train. Each articulated car has a total passenger capacity of 264 passengers. It may be equipped with two DC motors for a total power output of 300 kW (400 hp) and a maximum speed of 80 km/h (50 mph), or with four AC motors for an output of 544 kW (730 hp) and speed of 88 km/h (55 mph).
As the length of a tram or light-rail train running on shared track is restricted to a maximum of 105 meters in Germany, up to four U2 cars may be used in a single consist on such track.
Frankfurt U2 cars use Scheren (diamond) or single-arm (z-shaped) pantographs, while Calgary, Edmonton and San Diego vehicles use a single-arm (z-shaped) pantograph.
Siemens–Düwag Type U3 is an upgraded version of the U2 with a slightly longer length and cosmetic changes. Introduced in 1977, they entered service in 1980 and were never exported outside of Germany's Frankfurt U-Bahn.