The tunnel, which opened on November 23, 1985, closed a gap in I-95 between Maine and Florida.  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.
The Fort McHenry Tunnel was constructed from June 1980 to November 1985, at a cost of about $750 million. The tunnel's annual traffic in 2009 was 43.4 million vehicles. As of July 1, 2013, the toll rate for cars is $4.00, paid in either direction. Vehicles with more than two axles pay additional amounts, up to $30.00 for six axles.
The Fort McHenry Tunnel was opened on time and under its budget, and it continues to be a vital transportation link in the Mid-Atlantic region. Soon after the Fort McHenry Tunnel opened, the nearby Baltimore Harbor Tunnel and Interstate 895, which had opened to traffic in 1957, were closed for extensive rehabilitation.
Before and during the Civil War, a tunnel had been dug from the Baltimore and Ohio Railroad's Camden Station south to the north side of Federal Hill, and then to Fort McHenry. During the construction of the Fort McHenry Tunnel, 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.