Fort McHenry Tunnel, Maryland

An immersed-tube tunnel that carries eight lanes of Interstate 95 traffic under Baltimore's harbor. Constructed over five years in the early eighties, for $750 million, the mile and a half long tunnel is currently the widest vehicular immersed-tube tunnel in the world. Immersed-tube tunnels are made by sinking pre-made tube sections into a trench that has been prepared to hold the tubes in place. In this case, the trench that was dug uncovered 3.5 million cubic yards of dredge spoil that was contaminated from years of industry in the Baltimore area. This spoil had to be specially treated and removed. It was finally used to create a container yard at Baltimore's Seagirt Marine Terminal Facility, adjacent to the Dundalk Marine Terminal.