The Big Dig Central Artery/Tunnel Project, USA

The Central Artery/Tunnel Project in Boston (Massachusetts, USA) is replacing its central artery elevated highway with an underground expressway that will run directly under the existing road and end with a two bridge crossing of the Charles River. The project was originally planned in 1982 and is expected to be completed by the end of the year 2004.

CENTRAL ARTERY

The new Central Artery is designed to meet Boston's future traffic demand as estimated by future projections. If no improvements are made, the existing Central Artery is believed to face a daily volume of 220,000 vehicles with 14-15 hours of congestion by 2010. In contrast, traffic volume on the new underground artery is expected to be 240,000 vehicles per day.

The existing elevated Central Artery, was built in the 1950s to serve 75,000 cars daily. Today more than 190,000 cars jam the Central Artery every day, creating a 10 hour traffic jam and accidents at a rate three times the State average.

The new Central Artery will also strengthen connections among Boston's air, rail, and seaport terminals. By offering travellers and shippers increased choice and flexibility among these different modes of transportation, the Project is contributing to the creation of an integrated, intermodal transportation system for the entire region.

THE BIG DIG PROJECT TIMESCALE

Planning for the Central Artery/Tunnel began officially in 1982. Construction began in September 1991 and the first project milestone, the Ted William's Tunnel under Boston Harbour from South Boston to Logan Airport, opened to the traffic on December 1995.

The Big Dig is presently about 65% completed. The new roadways are expected to be ready for public use by December 2004.

PROJECT CHARACTERISTICS AND COSTS

The project which is expected to cost about $7.7 billion has two major components:

• The six-lane elevated highway will be replaced with an eight-to-ten-lane underground expressway directly beneath the existing road, culminating at its northern limit in a 14 lane, two bridge crossing of the Charles River. When the underground highway is finished, the crumbling elevated road will be demolished and replaced by open space and modest development.
• The Massachusetts Turnpike will be extended from its current terminus south of downtown Boston through a tunnel beneath South Boston and Boston Harbour to Logan Airport. The first link in this new connection, the four lane Ted William's Tunnel under the harbour, was finished in December 1995.

The project spans 7.5 miles of highway, 161 lane miles in all, about half in tunnels. To put the tunnels in place the engineers have used a system called "Tunnel Jacking" which consists in pushing the tunnel under the railroad tracks by building a concrete pit in the ground, constructing a section of tunnel inside that box and then pushing it under the tracks.

The Big Dig also includes four major highway interchanges to connect the new roadways with the existing regional highway system.

LEAD CONTRACTORS

The Central Artery/Tunnel Project (which is part of the metropolitan Highway System) is managed and operated by the Massachusetts Turnpike Authority.

The management consultants which co-ordinate the project are Bechtel/Parson Brinckerhoff (B/PB) a joint venture of Bechtel Corporation and Parsons Brinckerhoff Quade & Douglas, Inc.

The main general contractors for the central artery are J.F.White/Slattery/Perrini, which had been awarded a contract of approximately $377 million for the construction of the section between North Street to Chordon Street. A contract value of $339 million has been awarded to Modern Continental/Kobayashi for the construction of the tunnel section between High to State Street, and the section by the MBTA Aquarium Station.

In all there are 117 separate construction contracts and 50 design contracts for the Big Dig project as a whole.