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

The Boston Central Artery/Tunnel project represented public works on a scale comparable to some of the great projects of the previous century―the Panama Canal and the Channel Tunnel. It received dozens of awards for engineering excellence and aesthetics. 

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.

The 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.

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Engineering firsts

The project entailed building state-of-the-art freeway segments only inches above 19th-Century public transit railways. Other efforts that expanded civil engineering boundaries included:

  • 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

By the numbers

  • 7.8 miles (12.6 kilometers) of highway made up of 161 lane-miles (nearly 260 lane-kilometers), about half in tunnels, built.
  • More than 16 million yards (12.2 million cubic meters) of soil excavated.
  • 3.8 million cubic yards (12.2 million cubic meters) of concrete placed.
  • More than 300 acres of new parks and open space created.
  • Seven building ventilation system for the tunnels—one of the largest such system in the world.
  • 62 percent decrease of total vehicle-hours of travel on the project's highways between 1995 and 2003, saving travelers approximately $168 million annually due to shorter travel times and lower transportation costs.
  • Up to 74 percent decrease in travel times from the I-90/I-93 interchange to Logan International airport.
  • 12 percent drop in carbon monoxide levels citywide because of the new highway system- keeping traffic moving, reduces emissions significantly.

A 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 bridge's 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 point north. 

Keeping the city open during construction

Completing the project in the middle of Boston without crippling the city was an incredible challenge. 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.

Work of this magnitude and duration had never been attempted in the heart of an urban area. To keep it on track, project planners worked with environmental and other oversight and permitting agencies, community groups, businesses, and political leaders in order to create consensus on how the project would be built.

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.