42°21'15"N | 71°3'15"W

Boston Central Artery, Massachusetts, USA Overview

Scope of Work Management consultant: design and management of construction, procurement, and safety programs
Value $14.8 billion
Schedule 1991–2006
Business Infrastructure

The most complex urban transportation project in U.S. history

The Boston Central Artery/Tunnel project was the largest and most complex urban transportation project ever undertaken in the United States. The immense project―the result of more than 30 years of planning and 12 years of construction―replaced the elevated section of Interstate 93 Central Artery through downtown Boston with a much wider underground highway and extended the Interstate 90 turnpike to Logan International Airport via a third harbor tunnel. Bechtel and its joint-venture partner, Parsons Brinckerhoff, provided overall program management for the project.

Inside the Project

Award winning

The project received dozens of awards for engineering excellence and aesthetics. 

Big numbers

  • The project spanned 7.8 miles (12.6 kilometers) of highway, 161 lane-miles (nearly 260 lane-kilometers) in all, about half in tunnels.
  • Crews excavated more than 16 million yards (12.2 million cubic meters) of soil.
  • The Central Artery/Tunnel project team placed 3.8 million cubic yards (12.2 million cubic meters) of concrete.

Boston central artery revere park

The Central Artery/Tunnel project created more than 300 acres of new parks and open space.

Central Artery Tunnel project

Cutting-edge civil engineering

The Boston Central Artery/Tunnel project entailed building state-of-the-art freeway segments only inches above 19th-century public transit railways. That and other related efforts expanded a number of civil engineering boundaries:

  • The world's widest cable-stayed bridge
  • The deepest underwater connection in North America
  • An unprecedented ground-freezing program to stabilize Boston's soils during construction and to stabilize historic structures

Bridge already a modern Boston monument

The 10-lane cable-stayed hybrid bridge is the widest ever built and the first with an asymmetrical design. Designed by Swiss bridge specialist Christian Menn, the willowy bridge ties cables from the roadbed directly to the support towers. Atlanta and other cities have requested similar designs.

The bridge carries two outer lanes cantilevered on its east side. An additional eight lanes pass through the legs of the twin 300-foot (91-meter), obelisk-topped, inverted Y towers that echo the nearby Bunker Hill Monument. The bridges cables―which suggest a ship in full sail ―also evoke the history of East Boston as a center of shipbuilding. The bridge picks up Interstate 93 traffic as it emerges from the new Central Artery tunnel and carries it across the Charles River to points north. 

Keeping the city open for business during construction

Completing the Boston Central Artery/Tunnel Project in the middle of Boston without crippling the city was an incredible challenge. Work of this magnitude and duration had never been attempted in the heart of an urban area. But unlike any other major highway project, it was designed to maintain traffic capacity and access to residents and businesses throughout construction.

Recognizing that failing to maintain Boston's economic viability during construction would damage the city's competitive position for years to come, project planners worked with environmental and other oversight and permitting agencies, community groups, businesses, and political leaders to create consensus on how the project would be built. 

Big Dig concrete work

The project's seven-building ventilation system is one of the largest highway tunnel ventilation systems in the world.

Leonard P. Zakim Bunker Hill Bridge

Boston has already become known for the Leonard P. Zakim Bunker Hill Bridge over the Charles River. 

Why it matters

Congested highway created economic and quality-of-life drain

Boston had a world-class traffic problem. The elevated six-lane highway called the Central Artery, which ran through the center of downtown, was carrying upwards of 200,000 vehicles a day by the early 1990s, making it one of the most congested highways in the United States. Traffic crawled for more than 10 hours each day and 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.

The completion of the Central Artery/Tunnel Project changed all that. Due to traffic improvements and substantial reductions in traffic delay, the total vehicle-hours of travel on project highways dropped 62 percent between 1995 and 2003―saving travelers about $168 million annually in shorter travel times and lower transportation costs. Average travel times from the I-90/I-93 interchange to Logan International during peak periods decreased between 42 and 74 percent, depending on direction and time of day.

Nashua street park

Reconnecting neighborhoods helps revitalize city

Traffic wasn't the only problem that 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 downtown, limiting these areas' ability to participate in the city's economic life. The project reconnected neighborhoods severed by the old elevated highway and improved the quality of life in the city beyond the limited confines of the new expressway.

Big Dig improves traffic

Improving traffic, the environment, and the economy

The Central Artery/Tunnel project significantly reduced traffic congestion and improved mobility in one of America's oldest and most congested major cities. In addition, it helped improve the environment, and it established the groundwork for continued economic growth for Massachusetts and New England.

Because of the new highway system, Boston's carbon monoxide levels dropped 12 percent citywide. How can a road carrying more cars reduce pollution? Because it keeps traffic moving, reducing emissions significantly.

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