The Siemens–Duewag U2 is a type of light rail vehicle (LRV), built by consortium of Siemens, Duewag and Wegmann & Co built between 1968 and 1990. The design was based on the prototype U1 tram built in 1965 for the Frankfurt U-Bahn. The U2 was also designed for and used by the Frankfurt U-Bahn. The name is derived from the class identifier given to the cars in the Frankfurt. The U2 was later exported to North America and adapted for use on light rail systems in Edmonton, Calgary, and San Diego, during a period in which few purpose-built LRVs were being manufactured. History U1 prototype In the early 1960s, Duewag developed and manufactured a prototype of a new tram for the Frankfurt U-Bahn. The design was largely based on the previously delivered trams, but added electronic controls that allowed several railcars to be coupled together to form trains, and a floor height of that made it possible to board from platforms with a height of without having to add a folding step previously used. The new car was debuted at the International Transport Exhibition in Munich in 1965 and two vehicles arrived in Frankfurt in May 1966. There was no further production of the U1, and they were only used in regular service for a few years before being retired in 1976 because of their incompatibility with the rest of the fleet. U1 production vehicles With the experience learned from the two prototypes, several changes were made for the production series of cars. The vehicles were built by consortium of Siemens, Duewag and Wegmann & Co. Duewag was the primary developer and manufacturer, Siemens provided the electrical equipment, and Wegmann did some assembly under contract. The U2 vehicle was originally developed for the light rail system in Frankfurt. Its design was later used for systems in Edmonton and Calgary. The model was chosen for operations in San Diego in 1979, however, the planned platform level was lower than their counterpart system, so a street-level version was developed, and 71 vehicles were eventually delivered in stages. In Mendoza San Diego Metropolitan Transit System exported 11 cars to the Metrotranvia Mendoza system in Argentina in early 2010. These cars entered service in 2012 with a further 24 for expansion and parts donors following later that year. Refurbishment Edmonton Transit Service refurbished all 37 of its U2s to extend their operational life by