Apparently the original proposal was to build a tunnel there, which would have made a lot of sense for a whole host of reasons (not the least of them being to keep the shipping channel clear), but it was rejected as too expensive. If that was the case in 1971, I can't begin to fathom (pun intended) how much more expensive a tunnel would be nowadays. This isn't going to be a quick fix like the small concrete overpass on I-95 near Philadelphia last year.
(Interestingly, the place they had originally planned a bridge, rather than a tunnel, was for I-95 where the Fort McHenry Tunnel is now. The bridge plan quite rightly failed because of the impact it would have had on the historic site.)
