Part 1; the history of the Baltimore Harbor Tunnel
During 1938 and 1944 the Maryland State Road Commission conducted feasibility studies regarding constructing a bridge over the Patapsco River southeast of Baltimore Harbor. During 1947 the Maryland General Assembly passed an act to allow financing for the Patapsco River Crossing to be funded from toll revenues from the Potomac River Bridge, Susquehanna River Bridge and incomplete Chesapeake Bay Bridge. A feasibility study during 1953 examined three potential crossings for the Patapsco River crossing and considered if it should be a bridge or tunnel. During 1954 the Maryland State Road Commission opted to construct the Patapsco River Crossing as a tunnel between Baltimore neighborhoods of Canton and Fairfield.
Construction of the Patapsco River Tunnel would commence on April 7, 1955. The Patapsco River Tunnel was designed by New York engineering firm Signstad & Baillie. The Patapsco River Tunnel was constructed out of 21 segments of 310-foot-long tunnel. The first segment of the Patapsco River Tunnel was sunken into place on April 11, 1956.
The planned routing of the Patapsco River Tunnel can be seen on the 1956 Shell Highway Map of Baltimore.
The Patapsco River Tunnel segments were covered with rock fill via a cut and cover method during construction. The Patapsco River Tunnel would be rebranded as the Baltimore Harbor Tunnel upon being opened to traffic on November 29, 1957. The Baltimore Harbor Tunnel was part of the initial segment of the Harbor Tunnel Thruway between US Route 40/Pulaski Highway south to the planned Glen Burnie Bypass. The Baltimore Harbor Tunnel and Harbor Tunnel Thruway permitted a bypass of downtown Baltimore and 51 traffic lights.
The completed Baltimore Harbor Tunnel and initial segment of the Harbor Tunnel Thruway can be seen on the 1961 United States Geological Survey Map of Baltimore.