For ships do pass over I'd guess, I'm sure that's what they did it for? I-10 does the same thing going under Mobile Bay. Running a causeway for 10-12 miles up on stilts going westbound and you don't know you're going under 'til you're rite on top of that tunnel. First time I ran that road in that direction I'm maybe 2 miles away from it and I see a freighter crossing I-10 and I knew something waz up, lol. Jer