Line 12, also known as the Golden Line from its color on the system map, is a partially closed rapid transit line of the Mexico City Metro network. It travels along the boroughs of Benito Juárez, Iztapalapa and Tláhuac in southwestern, central-southern and southeastern Mexico City, serving twenty stations. The line was inaugurated on 30 October 2012, going from Tláhuac to Mixcoac station. In 2016, work to expand it to Observatorio station started. Line 12 was built by Mexican construction company Empresas ICA in association with Alstom Mexicana and Grupo Carso. It runs at grade, overground and underground levels. The interchange stations are Mixcoac (Line 7), Zapata (Line 3), Ermita (Line 2) and Atlalilco (Line 8), and when completed, Observatorio (Line 1). The line connects with other transport systems in the city, including the trolleybus and the Metrobús systems. In 2019, Line 12 had a total ridership of 134,900,367 passengers, averaging 369,590 passengers per day. Since its planning, the line underwent several modifications in its layout and characteristics. It was originally planned as a mostly subway line that would operate with rubber-tired trains. Also, the line would not operate primarily along Tláhuac Avenue. However, due to time and budget constraints the project underwent modifications after its announcement, and it became a combined under- and overground line with steel-tired trains running elevated along Tláhuac Avenue. Subsidence was reported on several columns along the elevated section before testings with trains started. From the onset of service, problems on the line were still reported especially on the elevated part of the line. In early 2014, operations were halted on that section and they were resumed until late 2015. The elevated track later suffered the impact of a earthquake in September 2017. In May 2021, a portion of the line's overpass collapsed while a train was on it. 26 people were killed and line operations had to be suspended. Preliminary investigations have suggested that the bridge had a deficient and questionable construction. On January 15, 2023, the section from Mixcoac to Atlalilco reopened for service. History Origins In the 1980s, the Comisión de Vialidad y Transporte Urbano (COVITUR), an organization of the Federal District Department, presented a plan for the Mexico City Metro based on several studies and reports related to the rapid growth of the city and its demand for public transportation. On the 1985 Metro Master Plan (Spanish: Programa Maestro del Metro