FWIW, I think there are even more errors in my figures. That said, I wasn't trying to bunk or debunk, as much as the grandparent's comment intrigued me enough to wonder "What if earthen barrier?" -- how much earth would that take. My guess was that it would be prohibitive, and that 116,000 tonnes traveling 8.5 knots is just too much to stop. Earth obviously can, as whomever alluded to the Ever Given points out, but a lot would be required. How much? I don't know, but I was just trying to get an idea.

You're right that it's amateur. This isn't remotely what I do. To your point though, I don't have that much confidence that the Skyway bulwarks would do -- I'm sure they're more than adequate in preventing strikes from my 40' sailboat. Probably much more than that. My gut tells me they are inadequate to stop the momentum of 100k tonnes at speed, but if they did SOMEthing, perhaps that would be enough to differentiate between bridge damage and bridge collapse. I can't find any details on how it's reinforced, with what, or how deeply those reinforcements are buried, so this too is wild speculation... but I wonder if it isn't somewhat security theater. My wife is already scared of bridges, and we're Marylanders who frequent that bridge and the (much longer) bay bridge -- putting something down there to calm her nerves enough that she isn't panicking for the duration of every crossing is almost certainly worthwhile, but doesn't leave the nerds much to ponder.