Bering Strait
There have been ideas of building a bridge or tunnel to link Alaska and Russia, where cars and trains could cross the strait. The crossing would have three parts, one connecting Big Diomede Island to Russia, one connecting Small Diomede with Alaska, and a final link between the islands. This would link the North American road system with the connected road systems of Asia, Europe, and Africa. There have not been any physical work done on such a crossing, mostly due to the remoteness of the strait, and the little demand for it. There are no major highways or railroads that connect the Bering Strait to the rest of Asia or America, so if either a tunnel or bridge was built across the strait, new connections to the rest of the highways and railways would have to be made for cars or trains to get there. The crossing might become more useful in the future however.