Named for nearby Fort McHenry, the tunnel is the lowest point in the Interstate Highway System under water.

Having consumed some $750 million (equivalent to $2.1 billion in 2023), it was the most expensive Interstate project until surpassed by the Big Dig in Boston.

[6] The tunnel crosses the Patapsco River, just south of Fort McHenry; it connects the Locust Point and Canton areas of Baltimore City.

In 1975, plans were changed to a tunnel after it was determined that a bridge would hurt Fort McHenry's status as a national monument.

After the Francis Scott Key Bridge collapsed on March 26, 2024, the tunnel became one of the primary alternate routes for drivers and trucks containing non-hazardous loads.