The Boston Big Dig was the Central Artery/Tunnel Project, a sixteen-year effort to bury Interstate 93 beneath downtown Boston, extend Interstate 90 through a harbor tunnel to Logan Airport, and tear down the elevated green steel highway that had cut the city off from its waterfront since the 1950s. It opened in stages between 1995 and 2006, cost $14.8 billion in direct spending (more than $24 billion with interest), and remains the most expensive public works project in American history. Along the way it produced a fatal ceiling collapse, a federal securities case over concealed cost overruns, criminal pleas by contractors, and a 17-acre park on top of the buried highway.
What the Big Dig Built
The project replaced a six-lane elevated highway with an eight-to-ten-lane underground expressway and added a new harbor tunnel linking the Massachusetts Turnpike to Logan Airport and the South Boston Seaport. In total it produced 161 lane miles of new highway, nearly half of it underground, across 7.5 miles of right-of-way.1National Academies. Completing the Big Dig It also delivered the Silver Line transit route and roughly 5,000 miles of fiber optic cable.2Federal Highway Administration. Boston Central Artery/Tunnel Project Profile
Three structures became the project’s public face. The Ted Williams Tunnel, the first segment to open, runs 0.75 miles under Boston Harbor and was built from twelve enormous elliptical steel tubes fabricated in Baltimore, towed north on barges, and lowered into a dredged trench on the harbor floor.3PBS. The Ted Williams Tunnel The Leonard P. Zakim Bunker Hill Memorial Bridge carries ten lanes of I-93 across the Charles River on a cable-stayed span whose towers echo the shape of the nearby Bunker Hill Monument; it is the only asymmetrical cable-stayed bridge in the United States and cost $115 million.4Rosales + Partners. Zakim Bridge And where the elevated artery once stood, the Rose Kennedy Greenway now runs 1.25 miles from Chinatown to the North End. Engineers used slurry-wall construction, immersed-tube tunneling, and tunnel jacking at a scale that had not been attempted in North America.
Why Boston Needed to Replace Its Highway
The old Central Artery was an elevated steel structure standing 30 to 50 feet above the streets of downtown Boston, designed in the 1948 Massachusetts Master Highway Plan to move 75,000 vehicles a day on six lanes. It opened in sections between 1959 and 1964, carved through the North End, West End, and Haymarket, and displaced roughly 20,000 residents.5Mass.gov. The Big Dig: Project Background The completed structure walled off entire neighborhoods from the waterfront.
By the early 1990s the highway was carrying more than 200,000 vehicles a day, nearly triple its design capacity, and had become one of the most congested roads in the country.2Federal Highway Administration. Boston Central Artery/Tunnel Project Profile Traffic crawled for more than ten hours each day, forecasts projected sixteen-hour jams by 2010, and the accident rate ran at four times the national average. Delays, wasted fuel, and crashes cost motorists an estimated $500 million a year.5Mass.gov. The Big Dig: Project Background
How It Got Approved and Funded
The idea of burying the artery dated to the early 1970s. Frederick Salvucci, an MIT-trained civil engineer who served as Massachusetts Secretary of Transportation under Governor Michael Dukakis from 1975 to 1978 and again from 1982 to 1991, made a strategic choice that defined the project: he merged the plan to depress I-93 with a separate proposal to extend I-90 through a harbor tunnel to Logan Airport. Combining the two unified environmentalists who wanted the elevated highway gone with business interests who wanted better airport access.6PBS. Frederick Salvucci Interview
Formal planning and environmental impact studies began in 1982, and the Federal Highway Administration approved the Final Environmental Impact Statement in 1985. Federal funding was secured in the 1987 highway bill through the efforts of House Speaker Thomas P. “Tip” O’Neill and Senator Edward Kennedy. President Ronald Reagan vetoed the bill, calling it a “textbook example of special-interest, pork-barrel politics at work.”7American Enterprise Institute. The Big Dig and the Shovel Brigade Congress overrode the veto, with the Senate doing so by a single vote after Mitch McConnell broke with his party to secure highway funding for Kentucky.8WGBH News. As House Speaker, Tip O’Neill Got the Big Dig Passed The main tunnel was later named for O’Neill. The Federal Highway Administration issued the formal construction go-ahead in 1991, and ground was broken that September on the South Boston bypass road and the Ted Williams Tunnel.
What It Cost, and the Concealment Scandal
When Congress approved the project in 1987, the estimated cost was $2.5 billion and the target completion date was 1998.9Taxpayers for Common Sense. Big Dig: Billions Over Budget The final direct cost came in at $14.8 billion, and once interest on the state bonds used to finance it is included, the true cost exceeded $24 billion. Funding came from roughly $7 billion in federal aid and $7.8 billion in state bonds, which are scheduled to be repaid through tolls and taxes by 2038.2Federal Highway Administration. Boston Central Artery/Tunnel Project Profile
The overruns were not just a matter of underestimation. James Kerasiotes, chairman of the Massachusetts Turnpike Authority from 1996 to 2000, ran the project as what he called a “zero sum game,” requiring staff to offset every cost increase and refusing to approve higher budget estimates until costs were “absolutely certain.”10U.S. Securities and Exchange Commission. In the Matter of Massachusetts Turnpike Authority and James Kerasiotes By mid-1998, internal charts showed projected overruns above $1 billion. By late 1999, a review confirmed a shortfall of roughly $1.4 billion. Despite that knowledge, the Turnpike Authority issued three rounds of municipal bonds in 1999 with offering materials stating the project was “on time and on budget.”
On February 1, 2000, officials publicly disclosed the $1.4 billion overrun, hours after filing a financial report with the Federal Highway Administration that failed to mention it.11Government Executive. Black Hole A federal task force called the concealment “one of the most flagrant breaches of the integrity of the federal/state partnership” in the 85-year history of the federal highway program. Governor Paul Cellucci asked Kerasiotes to resign on April 11, 2000, after reviewing a 48-page federal audit that described him as “deceptively mum” about the overruns.12The New York Times. Big Dig Chief Is Forced Out in Boston
The Securities and Exchange Commission later brought cease-and-desist proceedings against Kerasiotes and the Turnpike Authority for violating the Securities Act of 1933 by negligently misrepresenting the project’s financial condition in bond offerings. Both consented to the order without admitting or denying the findings. The SEC noted that Kerasiotes had not profited personally and that no bond investors suffered financial losses.10U.S. Securities and Exchange Commission. In the Matter of Massachusetts Turnpike Authority and James Kerasiotes
The 2006 Ceiling Collapse and Milena Del Valle’s Death
On July 10, 2006, a 26-ton section of the concrete suspended ceiling in the I-90 Connector Tunnel collapsed onto a car carrying Angel and Milena Del Valle. Milena Del Valle, 39, was killed. Angel Del Valle was injured, and the tunnel closed for months.13Mass.gov. Powers Fasteners Deferred Prosecution Agreement
The National Transportation Safety Board determined that the collapse was caused by an epoxy product called “Fast Set,” made by Sika Corporation and marketed by Powers Fasteners, Inc., which had been used to secure the ceiling’s steel anchors to the tunnel walls. The epoxy had poor “creep resistance” and was unsuitable for the sustained overhead loads the tunnel design imposed. Federal investigators also faulted Bechtel/Parsons Brinckerhoff, the project’s management team, and the section designer for failing to account for long-term creep.14Bechtel. Bechtel and Parsons Brinckerhoff Reach Settlement on Big Dig
Powers Fasteners was indicted in Suffolk Superior Court on one count of involuntary manslaughter. Prosecutors alleged the company had known since 1999 that its epoxy was failing in sustained-load applications and had withheld that information from project officials. In December 2008, Powers entered a deferred prosecution agreement with Attorney General Martha Coakley, agreeing to permanently stop selling Fast Set, recall the product, and notify industry entities about its failures. If the company complied for three years, the manslaughter charge would be dismissed; the agreement did not constitute an admission of liability.13Mass.gov. Powers Fasteners Deferred Prosecution Agreement Powers also paid $16 million to resolve criminal and civil cases and was barred from doing business with state and local governments until 2012.15CBS News. Co. to Pay $16 Million in Big Dig Collapse
The Del Valle family filed a separate wrongful death lawsuit against 15 defendants and reached a $28.09 million settlement. Bechtel/Parsons Brinckerhoff and Modern Continental paid a combined $15.4 million, Powers Fasteners contributed $6 million, and several other firms covered the rest.16Boston Herald. $28M Settlement in Fatal Big Dig Collapse
Contractor Settlements and Construction Fraud
In January 2008, Bechtel/Parsons Brinckerhoff and a group of smaller design firms reached a settlement of roughly $458 million with state and federal authorities to resolve claims arising from the ceiling collapse, thousands of tunnel leaks, defective concrete, and errors in construction drawings. Bechtel’s share was $352 million; Parsons Brinckerhoff paid about $47 million.14Bechtel. Bechtel and Parsons Brinckerhoff Reach Settlement on Big Dig The settlement also resolved False Claims Act allegations, directing more than $23 million to the United States and over $40 million to Massachusetts.17Phillips & Cohen. Big Dig Contractors Agree to Pay $458 Million U.S. Attorney Michael Sullivan said the consortium “grossly failed to meet their obligation and responsibilities.” Authorities said they had sufficient evidence to indict for manslaughter but declined because corporate penalties for the offense in Massachusetts were capped at $1,000.18NPR. State, Contractors Settle Suit Over Big Dig Failures Under the settlement, Bechtel remained liable for potential catastrophic incidents for ten years, with liability capped between $50 million and $100 million.
Concrete fraud produced the project’s other major criminal case. In August 2007, concrete supplier Aggregate Industries NE pleaded guilty to conspiracy to defraud the federal government. Between 1996 and 2005, the company had delivered approximately 5,700 truckloads of substandard concrete to the project. Employees recycled concrete that exceeded the 90-minute freshness limit, mixed it with new batches to disguise its age, and falsified batch slips for inspectors in a practice workers called “10-9 loads.” Aggregate agreed to pay $50 million ($42 million in civil penalties and $8 million in criminal fines) and to provide up to $75 million in insurance coverage for future structural maintenance costs attributable to the defective concrete, available for 30 years.19U.S. Department of Justice. Aggregate Industries Plea Agreement Six company managers were indicted on a 135-count federal indictment in May 2006. All six were later convicted.20U.S. DOT Office of Inspector General. Aggregate Industries Indictment
Beyond the collapse and the concrete, the project was plagued by water intrusion. A breach in the I-93 northbound tunnel wall in September 2004, attributed to construction contractor errors and inadequate oversight, prompted inspection of 1,600 wall panels; by April 2005, 102 defects had been identified, with two requiring major repairs, and more than a thousand low-level leak injection points required sealing.21U.S. Department of Transportation. Issues Concerning the Boston Central Artery/Tunnel Project
What Boston Got Out of It
By the numbers, the new highway system delivered substantial congestion relief in its first years. Total vehicle hours on project highways dropped 62 percent between 1995 and 2003. During peak periods, travel times from the I-90/I-93 interchange to Logan Airport fell by 42 to 74 percent, saving travelers an estimated $168 million a year in time and fuel costs.5Mass.gov. The Big Dig: Project Background The longer-term picture is more mixed. A Harvard Kennedy School analysis ranked Boston the most congested city in the United States in 2018 and noted that the “persistence of high traffic levels in the city and region reveals the limits of roadway construction,” pointing to induced demand as new capacity attracts new trips.22Harvard Kennedy School. Central Artery/Tunnel Project Analysis
The project also achieved a 12 percent reduction in citywide carbon monoxide levels by eliminating hours of daily traffic idling on the elevated highway.23National Park Service. The Big Dig and Spectacle Island’s Environmental Restoration More than 16 million cubic yards of soil were excavated, and roughly a quarter of it was used to cap Spectacle Island, a former city dump in Boston Harbor. Landscape architect Clarissa Rowe oversaw the planting of more than 2,400 trees and 26,000 shrubs on the island over 15 years. The project handled some 435,000 cubic yards of contaminated or hazardous soils under permits requiring disposal at licensed facilities, and environmental mitigation ultimately accounted for more than a fourth of the total budget.24Environmental Protection Online. Dealing With the Big Dig
Economically, the project attracted more than $7 billion in private investment and added over 43,000 jobs along the I-93 corridor and in the South Boston Seaport District, spurring 10 million square feet of office and retail space, 7,700 new housing units (including 1,000 affordable units), and 2,600 hotel rooms.2Federal Highway Administration. Boston Central Artery/Tunnel Project Profile The I-90 extension gave the formerly industrial South Boston Seaport direct highway access, and the district grew to over 8 million square feet of commercial space and more than 350 companies.25Macalester College. Seaport District, Boston, MA A 2018 MIT study found that property values in South Boston grew faster than in the city as a whole, and median rents in the Seaport reached over $2,600 a month by 2017, compared with $1,320 for the rest of Boston. The state’s own post-project analysis acknowledged a “missed opportunity with value capture,” noting that private landowners along the new Greenway saw their land values surge without contributing a proportional share back to the public investment that created that value.
The Rose Kennedy Greenway
Where the elevated highway once stood, the Rose Kennedy Greenway opened in October 2008, running 1.25 miles from Chinatown through the Wharf District to the North End and covering roughly 17 acres of protected parkland. It includes fountains, splash pads, a carousel, public art, Armenian Heritage Park, Dewey Square Park, and more than 400 free annual events.26Federal Highway Administration. Rose Kennedy Greenway Park Project Profile The Massachusetts Department of Transportation owns the parklands and the tunnel beneath them. The Rose Fitzgerald Kennedy Greenway Conservancy, a nonprofit established in 2004, manages the park under a lease from MassDOT on a roughly $5 million annual budget funded by state money, private donations, endowment income, and a Business Improvement District created in 2017 that levies an assessment on properties within one block of the park. It is the only organically maintained public park in Boston.27Rose Kennedy Greenway. History
Legacy and Ongoing Maintenance
The project officially ended on December 31, 2007, concluding the joint venture between the Turnpike Authority and Bechtel/Parsons Brinckerhoff.28NBC News. Big Dig Officially Done Massachusetts now ranks third nationally in the total count and length of tunnels, and second in lane miles traveling through tunnels — much of that infrastructure a product of the Big Dig.29MassDOT. Asset Management and Performance Update 2023 MassDOT completed a major Sumner Tunnel restoration between 2022 and 2024, is planning rehabilitation of the Central Artery North Area Tunnel under City Square in Charlestown, and has applied for federal grants to assess tunnel vulnerability to coastal and riverine flooding.
The project’s influence extends well beyond Boston. Its cost overruns and oversight failures prompted new federal requirements for mega-projects, including mandatory project management plans for undertakings exceeding $1 billion and financial plans for those over $100 million.21U.S. Department of Transportation. Issues Concerning the Boston Central Artery/Tunnel Project It remains a reference point in national infrastructure debates, cited both as a cautionary tale about cost control and corruption and as a demonstration that replacing an urban highway with a park and underground tunnels can reconnect a city to its waterfront.