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The Mackinac Bridge is one of 68 bridges across the country that a federal agency said should undergo a safety review after an investigation into the March 2024 collapse of the Francis Scott Key Bridge in Baltimore. The state of Michigan should conduct a vulnerability assessment to determine the risk of the bridge collapsing in the event of a vessel collision and develop a comprehensive risk reduction plan, the National Transportation Safety Board recommended in a report last week. The Mackinac Bridge and 67 others were targeted because they were designed before the American Association of State Highway and Transportation Officials issued guidance in 1991 on bridge safety. The Mackinac Bridge was built in 1957; the Key Bridge was built in 1977. The Mackinac Bridge Authority, which is housed within the Michigan Department of Transportation and oversees bridge maintenance and operation, confirmed it is reviewing the NTSB recommendation. "As always, the (Mackinac Bridge Authority’s) highest priorities are the safety of our state’s most iconic bridge and the travelers who use it," said James Lake, a spokesman for the Michigan Department of Transportation. "While the vessel traffic in the Straits is much different than what many other bridge owners are seeing in their waters, we plan to perform the assessments recommended by the NTSB," he said. While the American Association of State Highway and Transportation Officials had previously recommended bridge owners evaluate catastrophic collapse vulnerability for bridges built before it issued its guidelines in 1991, it could not require such an assessment be completed. The Maryland Transportation Authority had not performed such a review before the Key Bridge was struck by the container ship Dali on March 26, 2024, according to the report. Had the Maryland Transportation Authority conducted a vulnerability assessment, the NTSB found, the authority "would have been aware that the Key Bridge was above the acceptable risk and would have had information to proactively reduce the bridge’s risk of a collapse and loss of lives associated with a vessel collision with the bridge." Under the vulnerability assessment formula, the Key Bridge was about "30 times above the acceptable risk threshold for critical or essential bridges," according to the NTSB. The report urges the Federal Highway Administration, the U.S. Coast Guard and the U.S. Army Corps of engineers to form a team to help the 30 owners of the 68 bridges in 19 states to evaluate and reduce the risk of a bridge collapse. Those 68 bridges were designed before the 1991 vulnerability assessment guidelines, they cross navigable waterways used by ocean-going vessels, they have a vertical clearance of at least 80 feet, they have substructures such as piers in the waterway and they meet a threshold of annual transits by ocean-going vessels. "The NTSB concludes that the 30 owners of 68 bridges over navigable waterways frequented by ocean-going vessels are likely unaware of their bridges’ risk of catastrophic collapse from a vessel collision and the potential need to implement countermeasures to reduce the bridges’ vulnerability," the report said. Aside from the Mackinac Bridge, other bridges identified as needing a vulnerability assessment were the Golden Gate Bridge in San Francisco, the Brooklyn and George Washington bridges in New York and the Sunshine Skyway Bridge in Tampa Bay. Of Michigan's major bridges over navigable waterways — the Blue Water, Sault Ste. Marie International, Ambassador, and the Mackinac — only the Mackinac Bridge has significant pier structures in the water similar to the Key Bridge. The Mackinac Bridge has been struck three times since 1968 — by a freighter, a boat and a crane-carrying barge — with no significant damage, the Michigan Department of Transportation said last year. In June 1968, a Greek freighter, the Castilla, hit the bridge's north tower pier. More recently, in 2021, a 30-foot boat hit the northern bridge piers, and, in May 2023, a crane on a barge that was passing beneath the structure hit the bottom of the bridge's suspended span. The Mackinac Bridge differs from the Key Bridge in length, with the Mackinac spanning more than four miles to the Key Bridge's one and a half miles, and in the types of ships passing beneath it. While some 1,000-footers in the Great Lakes may rival the Dali in length, they generally carry lighter loads and have shorter drafts. More: Freighters in Great Lakes, St. Lawrence Seaway lose power, steering about 20 times a year But a Detroit News investigation last year found the Great Lakes are no stranger to the type of shipping power losses believed to have led to the Dali crash. Freighters on the Great Lakes and St. Lawrence Seaway lost propulsion, steering or electrical power more than 200 times between 2012 and May 2022 and crashed with stationary objects on the waterways more than 60 times over that same decade, according to U.S. Coast Guard data obtained by The News. Just 20 of the 263 instances of allision or propulsion, steering or power losses over 10 years were considered serious marine incidents by the Ninth Coast Guard District.  eleblanc@detroitnews.com This article originally appeared on The Detroit News: Mackinac Bridge recommended for safety review after Baltimore bridge collapse

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