TWT - How was it built?

The underwater portion of the tunnel is actually made up of twelve binocular shaped steel tubes, which were assembled in a shipyard in Baltimore and barged up here to Boston in 1992 and 1993. One tube holds the eastbound (to Logan Airport) traffic, the other the westbound traffic. They are each approximately 40 feet in diameter and a little over 300 feet long.
The tubes were first worked on separately, as steel reinforced concrete was used on the walls and to build the road on which vehicles would drive inside the tunnel.
Berthed here at the Black Falcon Pier along the south Boston Waterfront during the outfitting, the tubes can be seen here in various stages of construction. As more concrete and steel was installed, the tubes began to sink lower into the water.
Simultaneously, the worlds largest dredging machine was digging a three-quarter of a mile-long trench in the harbor between the South Boston Waterfront and Logan Airport.
Once the preliminary work on the tubes was completed they were barged into the harbor, and then lowered into a trench dug between the South Boston waterfront and Logan Airport. 890,000 cubic yards of material was dug to make this trench. One by one the twelve tubes were lowered and connected to each other, forming the 3/4 mile long tunnel.
Then the tiling, lighting, ceiling panels, emergency systems, signage, and other finishing touches were installed.
Meanwhile, on both sides of the harbor, the land-based tunnels that bring traffic to and from the water tunnel were constructed. Most of this material dug up for these tunnels ended up on Spectacle Island, where it is being used to help cap a dump and create a new public park.
 
The Ted Williams tunnel is a total of 1.6 miles long, and is serviced by two vent buildings, one on each side of the harbor.
In each building, one set of fans forces fresh air in, while another set pulls exhaust out and disperses it. The Logan Airport "Vent Building 7" is the larger of the two, with 14 exhaust and 10 supply fans, while the South Boston "Vent Building 6" has 6 exhaust and 4 supply fans.
Among the tunnel's safety features are a computerized traffic monitoring system, closed circuit television, computerized traffic monitoring system, closed circuit television, and emergency response stations, situated on each side of the harbor, which can dispatch emergency vehicles and to an incident within minutes, which will help prevent traffic tie-ups.