Mexico City Metro overpass collapse

Mexico City Metro overpass collapse
Investigators on site the night of the collapse
Details
Date	3 May 2021; 3 years ago (2021-05-03) 22:22 CDT (UTC-5)
Location	Tezonco–Olivos elevated interstation Tláhuac Avenue, Tláhuac, Mexico City
Coordinates	19°18′18″N 99°03′41″W / 19.3049°N 99.0613°W / 19.3049; -99.0613
Country	Mexico
Line	Line 12
Operator	Sistema de Transporte Colectivo (STC)
Incident type	Railway collapse
Cause	Lack of functional studs and poor welds that led to fatigue in the collapse point
Statistics
Trains	1
Vehicles	1
Crew	1[2]
Deaths	26[1]
Injured	98[1]

On 3 May 2021, at 22:22 CDT (UTC−5), a girder overpass in the borough of Tláhuac carrying Line 12 of the Mexico City Metro collapsed beneath a passing train. The overpass and the last two cars of the train fell onto Tláhuac Avenue near Olivos station, killing 26 people and injuring 98 others. It was the Metro's deadliest accident in almost fifty years.

The line experienced technical and structural problems that led to a partial closure of the elevated section where the accident occurred between 2014 and 2015. An earthquake in 2017 further damaged the span; although it was repaired within a few months, residents reported problems still existed years later. The line was announced in 2007 as an underground line with the possibility of operating rubber-tired trains because of the instability of the city's soil. The line was scheduled to be opened by 2010 but due to the budget and time constraints, the project was modified to operate both underground and overground with steel-wheeled trains, which researchers have named as one of the causes of track instabilities and damage since the beginning of the line's operations. Empresas ICA, the company that built the system's other lines, constructed it with Alstom Mexicana and Grupo Carso—the latter owned by Carlos Slim.

Claudia Sheinbaum, mayor of the city, hired the Norwegian risk management firm Det Norske Veritas (DNV) to investigate the causes of the collapse; preliminary investigations found it was related to deficiencies in the construction of the bridge, and a lack of functional studs and poor-quality welds that led to fatigue in the collapsed beam. Further investigations led them to conclude the bridge was designed and built without quality standards, that the construction and the line's design changes had been inadequately supervised, that there was a lack of fixing and safety elements, and that periodic maintenance checks that would have detected the girder buckling had not been done—the last statement being contested by the city government.

Carso, the company responsible for the construction of the collapsed section, denied any wrongdoing but Slim agreed with the government of Mexico to repair the section free of charge. In December 2021, the office of the city's attorney general filed charges against ten former officials—including the project director—who were involved in the construction and supervision of the project in December 2021; as of July 2024, these are awaiting trial for manslaughter, injury, and property damage.