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The number of structurally deficient bridges is actually down by about 7,000 from 2017, but those bridges weren't fixed. The number fell because the Federal Highway Administration weakened the standards of what it means for a bridge to be deficient, the report explains.
The collapse of a bridge earlier this week in Tennessee is raising new alarms about the delicate state of infrastructure across the U.S.
Apparently there the answer is to either put the pylons in shallow enough water that big ships physically cannot reach them, or to create artificial reefs around them so that big ships physically cannot reach them. This particular bridge seems to have been uncommonly vulnerable compared to similarly large bridges over shipping lanes, because the closest supports to the channel where big ships can fit were closer together than is normal and they lacked any sort of artificial reef barrier, even though the water depth near them would have allowed barriers to be built.
Yeah that makes a lot of sense. "Just don't get hit" but unironically.