The Mackinac Bridge is at a lower risk of collapse from a vessel collision than the national threshold, according to a report released on Wednesday.
The Mackinac Bridge Authority said it contracted with consultant engineering firm Parsons to evaluate the bridge against the American Association of State Highway and Transportation Officials (AASHTO) design guidelines.
It comes after the March 2024 collapse of the Francis Scott Key Bridge in Baltimore after it was struck by a container ship. The National Transportation Safety Board called on the owners of 68 bridges — including the Mackinac Bridge — to evaluate the structures for risk of collapse.
According to the MBA, the study was submitted to the NTSB in March and reviewed the conclusions during its meeting on Wednesday.
“This report confirms what we’ve long believed to be true, that the risk of the Mackinac Bridge collapsing due to being struck by a vessel is extremely low,” Bridge Director Kim Nowack said in a statement. “We hope this gives greater assurance to everyone who crosses the bridge that there is very little danger of such a tragedy here.”
According to the MBA, the analysis took into account the bridge design and structural capacity, the characteristics of the Straits of Mackinac, and the size, type and frequency of vessels that navigate near the bridge.
According to the NTSB, the Francis Scott Key Bridge in Baltimore was almost 30 times above the acceptable risk threshold for critical or essential bridges.
“The AASHTO Method II vessel collision analysis determines a total annual frequency of collapse of 0.000097, corresponding to a return period of approximately 10,350 years, which is below the AASHTO limit of 0.0001 for critical bridges. For one-way vessel traffic, the calculated annual frequency was 0.000045. Both results lie comfortably within the acceptable probability thresholds established by AASHTO for critical infrastructure, confirming that the Mackinac Bridge meets the prescribed reliability criteria," the Mackinac Bridge review found.
