The pair of tunnels is 1.45mi. 7,650 feet (2.33 km) long, stretching from the south shore of the Patapsco River to the north shore near Dundalk. Each tunnel is 22 feet (6.7 m) wide and 14 feet (4.3 m) high, and accommodates two lanes in each direction. The maximum speed within the tunnel is 50 miles per hour (80 km/h).
Both portals have ventilation buildings, with a total of 32 fans in place to replace the air within the tunnels, which is drawn in through the tunnel floors and exhausted through the tunnel ceilings. The tubes themselves range from a depth of 50 feet (15.2 m) below ground to 101 feet (30.8 m) below ground.
The tunnel and approaches were designed by Singstad and Baillie, a New York-based engineering firm specializing in tunnel design, in association with the J.E Greiner Company, a local Baltimore-based firm. The tunnel was formed out of 21 310-foot (94 m) sections individually submerged into the harbor and secured with rocks and backfill; the first of these tunnel segments was sunk on April 11, 1956. The remainder of the tunnel was constructed using the cut-and-cover method, extending from the submerged tubes to the north and south portals.
The tunnel opened on November 29, 1957 (along with most of the Thruway), nearly two months ahead of schedule. At the time, the toll was forty cents. The day the tunnel was opened, it experienced heavy traffic for the first time as thousands of motorists traveled north to Philadelphia to watch the 1957 Army–Navy football game.