The Big Dig: The Megaproject That Tore Boston Apart—and Put It Back Together

31 Days of Boston — Day 30

Boston’s Central Artery/Tunnel Project moved a highway underground, reshaped downtown, and became synonymous with the promise and peril of megaprojects.

For decades, Boston’s elevated Central Artery cut through downtown, carrying traffic while creating a physical barrier between neighborhoods and the waterfront. Its replacement, the project everyone came to call the Big Dig, took years of planning, more than a decade of construction, and a price tag that became a national byword. It also gave Boston back a part of itself.

The Highway in the Sky

The Central Artery was built in the 1950s, during an era when American cities were reshaping themselves around the automobile. The elevated highway carried Interstate 93 through the heart of downtown, slicing between the North End and the rest of the city and separating downtown from the waterfront. Buildings were demolished and neighborhoods divided to make room for it.

Almost from the start, the artery was unpopular. Its steel structure cast shadows over the streets below, and the noise and grime made the surrounding area unpleasant. It was also badly congested, with traffic jams stretching for hours each day. By the 1970s and 1980s, planners were searching for a better solution, and Boston’s experience with the elevated highway helped fuel resistance to building more urban highways through its neighborhoods.

The Plan: Bury It

The solution became one of the most ambitious urban infrastructure projects in American history: move major highway sections underground, build new tunnels and connections, and reclaim surface space.

The Central Artery/Tunnel Project combined several goals. It would replace the elevated artery with a tunnel beneath downtown. It would extend the Massachusetts Turnpike, Interstate 90, through a new tunnel under the harbor to Logan Airport. And it would build a striking new bridge over the Charles River. The idea was to improve traffic flow while reconnecting the city above.

The engineering challenges were immense. Workers had to dig beneath a living city, through landfill, clay, and old foundations, while keeping the existing highway open above them. Subway lines, utilities, and historic buildings had to be protected. Sections of tunnel were floated into place and sunk into the harbor floor. Innovative techniques, including slurry walls and ground freezing, were used to excavate safely.

Engineering Triumph, Political Cautionary Tale

The project known as the Big Dig was an engineering achievement—and a political cautionary tale. Costs escalated. Delays, management failures, leaks, and safety controversies became part of its public identity.

Major construction began in the early 1990s, and the main highway segments opened in stages through the early 2000s. Along the way, the cost estimates rose dramatically, eventually reaching many times the original projections and making the Big Dig one of the most expensive highway projects in American history. Investigations, audits, and lawsuits followed.

The most serious problems involved safety. Leaks were discovered in tunnel walls. In 2006, ceiling panels in one tunnel collapsed onto a car, killing a passenger — a tragedy that led to inspections, repairs, and legal action. For many observers, the Big Dig became a case study in how complex projects can suffer from weak oversight, divided responsibility, and underestimated costs.

A Transformed City

Yet its physical transformation of Boston is undeniable. Where elevated highway infrastructure once dominated portions of downtown, new public spaces and connections emerged. The city and waterfront relate differently because of it.

After the old artery came down, a ribbon of parks and open space, the Rose Fitzgerald Kennedy Greenway, was created along the corridor where the highway once stood. The North End was reconnected to downtown. The waterfront became easier to reach on foot. The Leonard P. Zakim Bunker Hill Memorial Bridge, with its distinctive cable-stayed design, became a new symbol on the Boston skyline. Even the excavated soil found a use: much of it went to the harbor islands, helping transform Spectacle Island into a public park.

Today, many residents and visitors who walk the Greenway have never seen the old elevated highway. That forgetting is itself a measure of the change.

The Classic Boston Question

The Big Dig asks a classic Boston question: how much disruption is acceptable in order to remake a city for the next generation? Boston has been rebuilding itself for four centuries. The scale changes. The argument does not.

The city has always reshaped its landscape: leveling hills, filling coves and marshes to create the Back Bay and other neighborhoods, building wharves and railroads, and rebuilding after fires. Each project brought disruption, cost, and controversy. Each left a city that later generations took for granted. The Big Dig stands in that tradition, with all of its flaws and achievements.

For anyone planning large projects — in government, business, or community life — the lessons are clear:

• Be honest about costs. Underestimates erode trust when the true scale becomes clear.
• Make accountability clear. Complex projects need oversight with real authority.
• Keep the public benefit in view. The reconnected city is the reason the disruption was worth debating.
• Safety is not negotiable. Engineering ambition must never outrun inspection and quality control.

Seeing the Big Dig This Week

• Walk the Rose Kennedy Greenway from Chinatown to the North End and imagine the elevated highway overhead.
• View the Zakim Bridge from the North Point Park area or the Charlestown side of the river.
• Visit Spectacle Island by ferry and stand on land shaped in part by Big Dig excavation.
• Look for old photographs of the Central Artery to appreciate how dramatically downtown has changed.

Research & Further Reading

For deeper research, consult authoritative collections including the Massachusetts Historical Society, Boston Public Library, National Park Service, Library of Congress, Massachusetts Archives, and relevant museum and university collections. Readers should verify contested details against primary and scholarly sources.

Boston Made is an independent editorial and archival platform. Historical stories are intended to encourage further exploration of primary sources, museums, libraries, and scholarly research.