The tunnel, opened on November 23, 1985, closed a gap in the East Coast’s most important interstate route, Interstate 95, between Maine and Florida. It also is the largest underwater highway tunnel built by the immersed tube method and the widest vehicular tunnel ever built by that same method. At the time of its opening it was the most expensive underwater tunnel project in the United States, but that figure has since been surpassed by the Big Dig project in Boston, Massachusetts. The Ft. McHenry Tunnel is one of seven toll facilities operated and maintained by the Maryland Transportation Authority.
The toll rate in 2008 for cars is $2.00, paid in both directions. Vehicles with more than two axles pay an additional $2.00 per extra axle.
The tunnel's route near Fort McHenry, and below the shipping channel prompted, the design of the world’s first tunnel sections that curved both vertically and horizontally. The tunnel sections were manufactured in Port Deposit, Maryland, and they were floated to the site using tugboats.
The tunnel was built using the open-trench method, in which prefabricated tunnel sections were sunk in a trench dredged in the harbor’s bottom. The sections were then joined underwater. A dredge-disposal site for materials removed from the tunnel trench was created at the nearby Helen Delich Bentley Port of Baltimore Seagirt Marine Terminal, resulting in 136 acres (55 hectares) of new, usable land. The Ft. McHenry Tunnel was opened on time and under its budget, and it continues to be a vital transportation link in the Mid-Atlantic region.
Before and during the Civil War, a tunnel had been dug from the B & O Railroad's Camden Station south to the north side of Federal Hill, and then to Fort McHenry. During the consruction of the Ft. McHenry Tennel, some houses in the Federal Hill neighborhood collapsed when that brick-lined tunnel collapsed. That tunnel was probably built by the U.S. Army and fell from use after the Civil War.
Sources: Maryland Transportation Authority