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. Calgary Transit regularly couples up six U2 cars to shuttle them from Anderson Garage to Haysboro storage. These unique shuttle trains can be commonly seen after the evening rush hour. 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).
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.