Downtown San Diego's blocks. The MTS teamed up with the Utah Transit Authority, which faced a similar problem with its system. The solution for both agencies was a specialized design Siemens called the S70 US ("Ultra Short") which retains the low-floor design, but would be the same length as the older high-floor vehicles (). The MTS and SANDAG agreed to purchase a total of 65 vehicles, which would arrive between September 2011 and January 27, 2015. However, there was not enough funding to replace all 123 high-floor cars at once. The decision was made to retire the original Siemens-Duewag U2 LRVs, and operate three-car trains with the new low-floor LRVs in the front and back, and an older high-floor Siemens SD-100 car in the middle. In late 2010, work to rebuild the stations started at the Old Town Transit Center and worked south. By September 2, 2012, work was completed on the Old Town and Bayshore lines, allowing for a realignment of service. The Green Line was extended from its former western terminus in Old Town south to 12th & Imperial Transit Center's Bayside Terminal platform, while the Orange Line was truncated to Santa Fe Depot and the Blue Line to America Plaza. The new alignment means all lines now pass through downtown and created a universal transfer point for all lines at 12th & Imperial Transit Center. By January 9, 2013, all stations on the Orange Line had been rebuilt, allowing low-floor LRVs to begin service on a second line. Rebuilding of the remaining stations (all on the Blue Line) was completed by January 27, 2015, The project, including remaining station and track renovations, was completed in late 2015. Mid-Coast Trolley extension project In 2011, SANDAG received key approval for the Mid-coast extension of the Blue Line, running from the Old Town Transit Center to the University City community, serving major activity and employment centers such as the University of California, San Diego (UCSD) campus, three major hospitals on (and adjacent to) the campus, and University Towne Centre (UTC) shopping center. Construction began in October 2016, and train testing on the line began in late June 2021. The Mid-Coast extension opened on November 21, 2021. The Blue Line was re-extended north from its original northern terminus at America Plaza to run through five existing stations (up to and including its pre-2012 terminus, the Old Town Transit Center), and continuing