a pair of two-lane tunnels that carry Interstate 85 under the Patapsco River

Southern approach to the Baltimore Harbor Tunnel.

Located on the only direct route between Philadelphia and the South, Baltimore was once called "the worst city in the United States on the matter of taking care of its through-traffic." The Harbor Tunnel was built as part of a program designed to erase Baltimore's "worst city" designation. Officials selected a tunnel, rather than a bridge, to carry traffic under the river after experts were convinced that the costs of a twin-tube tunnel could be supported by the toll revenues it would generate.

Designed by Singstad and Baillie, in association with the J.E Greiner Company, the tunnel was formed out of 21 twin-tube steel segements, each of which was approximately 70 feet across and 300 feet long. Each segment was built in a nearby drydock and then towed out to the construction site, where it was placed in a dredged trench, connected to the preceding segment by divers, and covered with rock and backfill. The first segment was sunk on April 11, 1956, and the tunnel was opened to traffic on November 29, 1957. The total cost of the project, including approach roads, was $130 million, with the tunnel itself making up $44 million of that total.

Inside one of the steel tubes, before the ceiling, floor, and lining have been added.

Vintage cars emerge from the Harbor Tunnel after its dedication.

Maryland Transportation Authority http://www.mdta.maryland.gov/toll_facilities/bht.html
Toll Roads News http://tollroadsnews.com/news/baltimore-harbor-tunnel-is-50

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