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.
U2 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 Between 2011 and 2014
San Diego Metropolitan Transit System exported 18 cars to the
Metrotranvia Mendoza system in Argentina. Eleven of the cars were renumbered 1001–1011, nine entering service in 2012, and further two in 2019. The remaining seven cars were used as spare parts donors and were scrapped in 2022.
Refurbishment Edmonton Transit Service refurbished all 37 of its U2s to extend their operational life by another 10 years. Upgrades included overhauls to the mechanical and electrical systems, the addition of new LED interior and exterior destination signs, additional speakers to improve sound volume, and retrofits for CBTC operation for the Metro Line. Refurbishment was done by
Bombardier Transportation in
Buffalo, New York.
Retirement In 2010, the
San Diego Metropolitan Transit System sold 35 cars to Mendoza, Argentina, followed by the bulk of its U2 fleet retiring in 2013, when the
Orange Line received low-floor cars. The remainder were used on its
initial operating segment until January 2015. In 2016, two cars were shipped to
Texas for use at a dog training facility, The majority of the U2's had left the property by 2018, having been either scrapped or donated to museums, with car 1001 being retained. After 48 years of service, the last Frankfurt examples were retired in April 2016. The Frankfurt cars have been replaced by
Bombardier Flexity Swifts, there are three cars left for museum purposes. Calgary Transit has begun a similar retirement system as they have begun to introduce the
Siemens S200 as both a replacement and expansion of the fleet. The city has begun to explore additional disposition options. The U2s in Calgary had been retired in 2016 but there are still 40 in service out of 83 DCs and 2 ACs. In 2022, Edmonton Transit Service announced that its 37 U2s will be replaced by 2030, as they intend to procure new LRV's in the next eight to ten years. On February 6, 2026, the City of Edmonton awarded
Hyundai Rotem a contract for 32 high-floor light rail vehicles to replace the fleet of U2s, with deliveries from 2029 to 2030. ==Technical details==