Last week, the National Transportation Safety Board (NTSB) revealed its latest investigative findings related to the deadly collapse of the Florida International University (FIU) pedestrian bridge that killed six in Miami earlier this year. The bridge, which hovered over eight lanes of traffic at an already hazardous intersection at the university, was designed to minimize disruptions to the transportation below, and it featured an amenity deck and bicycle lane for students. Its March 15, 2018, collapse, which completely flattened the cars underneath, could have been the result of errors in its design, according to the NTSB.

Within the framework of the NTSB investigation, authorities from the Federal Highway Administration assessed the 174-foot-long, 950-ton span’s construction and found crucial design errors in the north end of the structure, where two trusses were connected diagonally to the bridge deck. According to the reports, the bridge’s designers overestimated the capacity of a major section of the bridge and underestimated the load that section would have to carry. Examiners also discovered that the cracks found in the northernmost nodal region prior to the collapse were related to the aforementioned design errors.

On August 9, 2018, the NTSB tested the concrete and steel used for the bridge, finding that there were no flaws in either of the materials. The report also included detailed pictures of the cracks at the north end of the bridge, which were minor before the span’s installation but transformed into fissure-like gaps by the time the structure was placed over the busy highway. Investigators believe the gaps contributed significantly to the bridge’s failure.

The Occupational Safety and Health Administration (OSHA) recognized safety violations on March 15, the day of the collapse, and hired five contractors to inspect the structure and implement repairs, including Munilla Construction Management. However, OSHA issued FIGG Bridge Engineers, a designer on the project, a serious violation with a fine of over $12,000 for putting employees in physical danger by permitting them to work on the bridge after the dangerous cracks were discovered.

The NTSB report is preliminary, and investigators are still searching for other design and technical flaws that led to the bridge’s failure.