Big Dig
The Big Dig was a megaproject in Boston that rerouted the elevated Central Artery of Interstate 93 into the O'Neill Tunnel and built the Ted Williams Tunnel to extend Interstate 90 to Logan International Airport. Those two projects were the origin of the official name, the Central Artery/Tunnel Project. The megaproject constructed the Zakim Bunker Hill Bridge over the Charles River, created the Rose Kennedy Greenway in the space vacated by the previous elevated roadway and funded more than a dozen projects to improve the region's public transportation system. Planning began in 1982 and construction was carried out between 1991 and 2006. The project concluded in December 2007.
The project's general contractor was Bechtel, with Parsons Brinckerhoff as the engineers, who worked as a consortium, both overseen by the Massachusetts Highway Department. The Big Dig was the most expensive highway project in the United States, and was plagued by cost overruns, delays, leaks, design flaws, accusations of poor execution and use of substandard materials, criminal charges and arrests, and the death of one motorist.
The project was originally scheduled to be completed in 1998 at an estimated cost of $2.8 billion, US$7.4 billion adjusted for inflation. The project was completed in December 2007 at a $14.6 billion, a cost overrun of about 97% when adjusted for inflation. As a result of a death, leaks, and other design flaws, the Parsons Brinckerhoff and Bechtel consortium agreed to pay $407 million in restitution, and several smaller companies agreed to pay a combined sum of approximately $51 million.
Origin
This project was developed in response to the persistent and growing problem of traffic congestion on Boston's historically tangled and narrow streets, many of which were laid out centuries before the invention of the automobile. The layout, originally designed for horse-drawn carriages and pedestrian traffic, was never intended to accommodate modern vehicles, leading to chronic bottlenecks and delays that frustrated commuters and residents alike. As early as 1930, the city's Planning Board recognized the urgent need to address these traffic issues and recommended the construction of a raised express highway running north–south through the downtown district. The goal was to create a faster, more direct route that would allow through-traffic to bypass the congested city streets, reducing travel times and improving the flow of vehicles throughout the area.Building on these early recommendations, Commissioner of Public Works William Callahan actively promoted detailed plans for what would become the Central Artery, an elevated expressway designed to run between the downtown district and the waterfront. The project was envisioned as a major infrastructure improvement that could transform urban mobility in Boston by separating local traffic from longer-distance through-traffic. Ultimately, the elevated expressway was constructed according to these plans, dramatically altering the cityscape while addressing some of the long-standing traffic challenges. Its development marked a pivotal moment in Boston's urban planning history, reflecting both the ambitions of city planners to modernize the transportation system and the broader nationwide trend during the mid-20th century toward building elevated highways through urban centers.
In the 1950s, Governor John Volpe interceded to change the design of the last section of the Central Artery, putting it underground through the Dewey Square Tunnel. While traffic moved somewhat better, the other problems remained. There was chronic congestion on the Central Artery, the elevated six-lane highway through the center of downtown Boston, which was, in the words of Pete Sigmund, "like a funnel full of slowly-moving, or stopped, cars."
In 1959, the road section carried approximately 75,000 vehicles a day. By the 1990s, this had grown to 190,000 vehicles a day. Traffic jams of 16 hours were predicted for 2010.
The expressway had tight turns, an excessive number of entrances and exits, entrance ramps without merge lanes, and as the decades passed and other planned expressways were cancelled, continually escalating vehicular traffic that was well beyond its design capacity. Local businesses again wanted relief, city leaders sought a reuniting of the waterfront with the city, and nearby residents desired removal of the matte green-painted elevated road, which mayor Thomas Menino called Boston's "other Green Monster", as an unfavorable comparison to Fenway Park's famed left-field wall. MIT engineers Bill Reynolds, and eventual state Secretary of Transportation Frederick P. Salvucci envisioned moving the whole expressway underground.
Cancellation of the Inner Belt project
Another important motivation for the final form of the Big Dig was the abandonment of the Massachusetts Department of Public Works' intended expressway system through and around Boston. The Central Artery, as part of Mass. DPW's Master Plan of 1948, was originally planned to be the downtown Boston stretch of Interstate 95, and was signed as such. A bypass road called the Inner Belt, was subsequently renamed Interstate 695. The law establishing the Interstate highway system was enacted in 1956.The Inner Belt District was to pass to the west of the downtown core, through the neighborhood of Roxbury and the cities of Brookline, Cambridge, and Somerville. Earlier controversies over impact of the Boston extension of the Massachusetts Turnpike, particularly on the heavily populated neighborhood of Brighton, and the additional large amount of housing that would have had to be destroyed, led to massive community opposition to both the Inner Belt and the Boston section of I-95.
By 1970, building demolition and land clearances had been completed along the I-95 right of way through the neighborhoods of Roxbury, Jamaica Plain, the South End and Roslindale. This led to secession threats by Hyde Park, Boston's youngest and southernmost neighborhood, which I-95 was also slated to go through. By 1972, with relatively little work done on the Southwest Corridor portion of I-95 and none on the potentially massively disruptive Inner Belt, Governor Francis Sargent put a moratorium on highway construction within the Route 128 corridor, except for the final short stretch of Interstate 93. In 1974, the remainder of the Master Plan was canceled.
With ever-increasing traffic volumes funneled onto I-93 alone, the Central Artery became chronically gridlocked. The Sargent moratorium led to the rerouting of I-95 away from Boston around the Route 128 beltway, and the conversion of the cleared land in the southern part of the city into the Southwest Corridor linear park, and a new right-of-way for the Orange Line subway and Amtrak. Parts of the planned I-695 right-of-way remain unused and under consideration for future mass-transit projects.
The original 1948 Master Plan included a Third Harbor Tunnel plan that was hugely controversial in its own right, because it would have disrupted the Maverick Square area of East Boston. It was never built.
Mixing of traffic
A major reason for the all-day congestion was that the Central Artery carried north–south traffic and east–west traffic. Boston's Logan Airport lies across Boston Harbor in East Boston. Before the Big Dig, the only access to the airport from downtown was through the paired Callahan and Sumner tunnels. Traffic on the major highways from west of Boston—the Massachusetts Turnpike and Storrow Drive—mostly traveled on portions of the Central Artery to reach these tunnels. Getting between the Central Artery and the tunnels involved short diversions onto city streets, increasing local congestion.Mass transit
A number of public transportation projects were included as part of an environmental mitigation for the Big Dig. The most expensive was the building of the Phase II Silver Line tunnel under Fort Point Channel, done in coordination with Big Dig construction. Silver Line buses now use this tunnel and the Ted Williams Tunnel to link South Station and Logan Airport.Construction of the MBTA Green Line extension beyond Lechmere to Medford/Tufts station opened in December 2022., promised projects to connect the Red and Blue subway lines, and to restore the Green Line streetcar service to the Arborway in Jamaica Plain have not been completed. The Red and Blue subway line connection underwent initial design, but no funding has been designated for the project. The Arborway Line restoration has been abandoned, following a final court decision in 2011.
The original Big Dig plan included the North-South Rail Link, which would have connected North and South Stations, the major passenger train stations in Boston. This aspect of the project was dropped by the state transportation administration early in the Dukakis administration. Negotiations with the federal government had led to an agreement to widen some of the lanes in the new harbor tunnel, and accommodating these would require the tunnel to be deeper and mechanically vented. This left no room for the rail lines. Diesel trains, then in use, passing through the tunnel would have substantially increased the cost of the ventilation system.
Early planning
The project was conceived in the 1970s by the Boston Transportation Planning Review to replace the rusting elevated six-lane Central Artery. The expressway separated downtown from the waterfront, and was increasingly choked with bumper-to-bumper traffic. Business leaders were more concerned about access to Logan Airport, and pushed instead for a third harbor tunnel.In 1982, planning for the Big Dig as a project officially began. In 1983, environmental impact studies started. In 1987, after years of extensive lobbying for federal dollars, a public works bill appropriating funding for the Big Dig was passed by the US Congress, but it was vetoed by President Ronald Reagan for being too expensive. When Congress overrode the veto, the project had its green light. In 1991, ground was first broken.
In 1997, the state legislature created the Metropolitan Highway System and transferred responsibility for the Central Artery and Tunnel "CA/T" Project from the Massachusetts Highway Department and the Massachusetts Governor's Office to the Massachusetts Turnpike Authority.
The MTA, which had little experience in managing an undertaking of the scope and magnitude of the CA/T Project, hired a joint venture to provide preliminary designs, manage design consultants and construction contractors, track the project's cost and schedule, advise MTA on project decisions, and, in some instances, act as the MTA's representative. Eventually, MTA combined some of its employees with joint venture employees in an integrated project organization. This was intended to make management more efficient, but it hindered MTA's ability to independently oversee project activities because MTA and the joint venture had effectively become partners in the project.