MEXICO CITY—A preliminary report by experts into the collapse of a Mexico City elevated subway line that killed 26 people placed much of the blame Wednesday on poor welds in studs that joined steel support beams to a concrete layer supporting the track bed.
The city government hired Norwegian certification firm DNV to study the possible causes of the May 3 accident, in which a span of the elevated line buckled to the ground, dragging down two subway cars.
