Why the Mexico City metro collapsed
By Natalie Kitroeff, Maria Abi-Habib, James Glanz, Oscar López, Weiyi Cai Evan Grothjan, Miles Peyton and Alejandro Cegarra
On a balmy night in May, Tania Lezama Salgado hopped on the metro with her sister Nancy after spending hours looking for the grandest pink dress and the sparkliest shoes possible for her 15th birthday party.
Tania had grown accustomed to the screeches and shakes of the metro, but as it barreled across an overpass that night — jerking violently, going faster than she had ever remembered — something felt different.
Suddenly, she heard a loud bang, then screams, as the overpass collapsed and the train plummeted about 40 feet to the street below. When Tania came to, her neck was wedged between the doors of the metro.
Tania now spends her days in the hospital, unable to walk, her shattered pelvis held together by a metal contraption. Above her hospital bed is a photo of her 22-year-old sister Nancy — one of 26 people who died in the metro crash that night.
Soon after, President Andrés Manuel López Obrador of Mexico, who positions himself as a champion of the poor and an enemy of the elite, apologized to the victims’ families and urged patience while officials examined what went wrong and who was to blame.
“The humble, hardworking, good people understand that, unfortunately, these things happen,” he said during a news conference Tuesday.
But a New York Times investigation — based on years of government records, interviews with people who worked on the construction, and expert analysis of evidence from the crash site — has found serious flaws in the basic construction of the metro that appear to have led directly to its collapse.
The disaster has already spiraled into a political crisis, threatening to ensnare two of the nation’s most powerful figures: the president’s foreign secretary, Marcelo Ebrard, and one of the world’s wealthiest businessmen, Carlos Slim.
Ebrard was mayor of Mexico City when the new metro line, known as the “Golden Line,” was built, a heralded expansion of the second-largest subway in the Americas that could boost his credentials for a possible presidential run. And Slim’s construction company, Carso Infrastructure and Construction, built the portion of the line that collapsed — the firm’s first rail project, paving the way for more.
The Times took thousands of photographs of the crash site and shared the evidence with several leading engineers who reached the same conclusion: The steel studs that were vital to the strength of the overpass — linchpins of the entire structure — appear to have failed because of bad welds, critical mistakes that likely caused the crash.
That is one of the primary explanations being considered by Mexico City officials, according to several people familiar with the official investigations into the disaster, and it underscores a pattern of political expediency and haphazard work as the metro was being built.
The Times reviewed thousands of pages of internal government and corporate documents on the metro’s troubled history, finding more than a decade of warnings and concerns about safety before the fatal crash.
— In a rush to finish, the city demanded that construction companies open the subway well before Ebrard’s term as mayor ended in 2012. The scramble led to a frenzied construction process that began before a master plan had been finalized and produced a metro line with defects from the start.
— Federal auditors found that the city “authorized poor quality work” even as the line was being built. The metro was certified less than an hour before it was inaugurated, even though thousands of pieces of work had not been completed, according to a 2014 investigation by the city’s Legislative Assembly.
— During an inspection after a major earthquake in 2017, the city found errors in the original construction of the section built by Slim’s company, including incorrectly poured concrete and missing steel components, according to an unreleased government document from 2017.
Major problems with the subway emerged early on. Pushing to finish before Ebrard left office, the city bought train cars that arrived quickly but were not compatible with the rail line; the wheels did not fit properly on the track. The result was a constant pounding, warping and rippling of what should have been smooth steel track.
Less than a year after certifying the line as safe, auditors produced a report documenting a litany of problems: cracked and broken parts, deformed tracks and a relentless pummeling of the tracks.
After more than a year of repairs, the city reopened it in 2015. But problems persisted, with concerns intensifying after a horrific earthquake in 2017.
In a statement to the Times, Ebrard said that “the issues observed” during construction of the metro line did not affect its operation. He suggested the cause of the crash may have been tied to maintenance.
But evidence from the crash site indicates that the metro’s flaws ran much deeper than maintenance.
Underneath the tracks, the line that carried more than 250,000 people around the Mexican capital every day was held together by boltlike studs. Welded into steel and encased in concrete, they created a structure much stronger than either material on its own.
The strength of the overpass depended on those studs; they were an essential connection keeping it intact.
But photographs of the rubble point to a fundamental lapse during construction: The welds holding everything together were far too weak. Photographs show that the studs broke clean off the steel beams, creating what engineers called an unstable structure incapable of supporting the train.
“A good quality weld would not have failed like that,” said Gary Klein, a member of the National Academy of Engineering and an executive at Wiss, Janney, Elstner, a firm that studies construction-related failures.
The studs were handled shoddily, with little attention to detail, engineers reviewing the photographs said. One obvious mistake: Workers never removed many of the ceramic rings used around the studs during installation. Many of those rings can be seen embedded in the concrete slabs that collapsed that night.
After an earthquake devastated the capital in 2017, the city did its own inspection and found other construction flaws in the portion built by Slim’s company. An internal government document from 2017 reviewed by the Times noted that parts of the overpass had “structural faults” and were missing steel components and that some of the concrete was badly poured.
Antonio Gómez García, CEO of Group Carso, Slim’s sprawling empire, acknowledged that leaving the ceramic rings around the studs was not ideal but said it had not affected the structure. He said he believed the studs sheared off only after the overpass crashed to the ground and “were not the cause of the accident.” He added that maintenance could be to blame, as the equipment and materials used to repair the line after it was shut down in 2014 were heavy, possibly putting too much stress on the overpass.
But several independent experts rejected that explanation, noting that the photographic evidence points directly to the weak welds as the likely cause of the accident.
Whatever the official investigations determine, the crash could carry immense consequences — not just for Ebrard and Slim (who was previously a large shareholder of The New York Times Co.). If maintenance played a role, voters may also blame the president’s protégé, Claudia Sheinbaum, who has overseen the metro as Mexico City’s mayor for the last two years.
As two of the most dominant figures in the governing party, Sheinbaum and Ebrard are widely expected to vie for López Obrador’s blessing to succeed him and run for president in the 2024 elections.
With the public outcry over the crash, Sheinbaum’s administration offered about $32,000 to each of the families that lost a loved one. But some have refused the money and are suing the Mexico City metro system instead.
“The line wasn’t made right,” said Bernarda Salgado López, the mother of Tania, who is still in the hospital, and Nancy, who died. Salgado has joined the lawsuit.
“I think they should be held responsible for what happened, for everything, for everyone who died,” she said.
To win the contract in 2008, Slim’s company, Carso Infrastructure and Construction, joined two established firms: one of Mexico’s largest construction companies, ICA, and Alstom of France. Carso had no experience building train lines, but it did have two attractive qualities: liquidity in the midst of the global financial crisis and access to a steel business owned by Slim.
After construction began, federal auditors discovered serious flaws. In a 2009 report, they documented “badly executed work” performed “without quality controls,” among other issues, noting that “there was inadequate communication” between the groups supervising the project and the construction companies.
The city put pressure on contractors to complete the job as quickly as possible. The companies faced a fine of about $120 million if they did not finish well before Ebrard’s term ended, according to Enrique Horcasitas, the project director. Construction began even before a master plan had been completed.
But the problem that drew the most public attention was the purchase of trains, which did not fit tightly enough on the tracks.
The mismatch stemmed from another timesaving decision. The rails were designed for American standards, according to testimony in the 2014 investigation by the city Legislature.
But the government ended up choosing a Spanish supplier, CAF, that provided trains designed for European specifications. The reason: CAF had promised to deliver the trains about a year ahead of its competitor, Canada-based Bombardier.
The incompatibility caused so much wear that the city had to replace a half-mile of rail weeks before the metro even started carrying passengers.
The metro director at the time, Joel Ortega, said during the 2014 investigation that after just a year in service, parts of the metro line showed signs of wear that should be expected after a decade of use. The same company that certified the line conducted an inspection a year after and found more than a dozen problems, including “abnormal warping” of tracks and poor welding.
“In an accident,” Ortega said, “not only would the train run off the track, but we would probably have an enormous tragedy.”