Big Dig

Big Dig is the largest single civil construction project ever undertaken in the US.

The Problem

Boston, Massachusetts had a world-class traffic problem, an elevated six-lane highway called the Central Artery that ran through the center of downtown. When itopened in 1959, the Central Artery comfortably carried about 75,000 vehicles a day. It carried upwards of 200,000, quite uncom-fortably, making it one of the most congested highways in the United States.

Traffic crawled for more than 10 hours each day. The accident rate on the deteriorating elevated highway was four times the national average for urban Interstates. The same problem plagued the two tunnels under Boston Harbor between downtown Boston and East Boston/Logan Airport. Without major improvements to the Central Artery and the harbor crossings, Boston expected a stop-and-go traffic jam for up to 16 hours a day – every waking hour – by 2010.

The annual cost to motorists from this congestion – in terms of an elevated accident rate, wasted fuel from idling in stalled traffic, and late delivery charges – was estimated at $500 million.

And traffic wasn’t the only problem the old Central Artery caused in Boston. The elevated highway (which displaced 20,000 residents when it was built) also cut off Boston’s North End and Waterfront neighborhoods from the downtown, limiting these areas’ ability to participate in the city’s economic life.

The Solution

This extraordinary traffic mess has represented a continuous economic and quality-of-life drain on Boston and New England. The solution, called the Central Artery/Tunnel Project (CA/T), was constructed under the supervision of and operation of the Massachusetts Turnpike Authority.

The project’s two major components:

Replacing the six-lane elevated highway 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. After the underground highway opened to traffic, the crumbling elevated was demolished and in its place is open space and eventually modest development.

The extension of I-90 (the Massachusetts Turnpike) from its former terminus south of downtown Boston through a tunnel beneath South Boston and Boston Harbor to Logan Airport. The first link in this new connection – the four-lane Ted Williams Tunnel under the harbor – was finished in December 1995.

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