Years of Unheeded Warnings. Then the Subway Crash Mexico City Had Feared. Mexico City’s subway system has been plagued with problems for years. On Monday, an overpass collapsed, and a train plunged some 50 feet, killing at least 24 people and setting off a political firestorm. Concerns about the structural integrity of the subway line that collapsed on Monday had been raised for years, including after a strong earthquake struck Mexico City in 2017.Credit...Alejandro Cegarra for The New York Times MEXICO CITY — The capital had been bracing for the disaster for years. Ever since it opened nearly a decade ago, the newest Mexico City subway line — a heralded expansion of the second largest subway system in the Americas — had been plagued with structural weaknesses that led engineers to warn of potential accidents. Yet other than a brief, partial shutdown of the line in 2014, the warnings went unheeded by successive governments.