The underwater section of the tunnel is 90 feet below the surface of Boston Harbor, the deepest such connection in North America.

[2] The Ted Williams Tunnel (TWT) was the first major link constructed as part of Boston's Big Dig.

At this point, the steel panels sealing the now-joined sections could be cut out and the finishing operations could be completed.

Massachusetts governor Mitt Romney ordered the eastbound lanes of the Ted Williams Tunnel to be immediately shut down on July 20 after two ceiling supports showed signs of slippage.

Cars heading to the airport northbound on the Southeast Expressway (I-93) would get off at exit 15B (former exit 18)[7] and take the South Boston Access (Haul) Road to Ramp A, eliminating the need to go through downtown Boston and U-turn at Storrow Drive to access the Callahan Tunnel.