Big Dig

Big Dig, the largest and most expensive highway infrastructure project in American history. Initially conceived in the 1970s and begun in 1991, it took 15 years of construction to reroute Boston’s major highway, Interstate Highway 93 (I-93), through an underground tunnel. The project was plagued with issues throughout its planning and construction, causing many delays and massive cost overruns. Once finished in 2007, however, the Big Dig successfully reduced traffic congestion in downtown Boston and created space for more than 45 public parks and plazas.

How did the Big Dig begin?

The Central Artery, an elevated highway running through the heart of Boston, opened in 1959. It had been designed for 75,000 daily travelers in 1959, but that number had ballooned to more than 200,000 in 1990. Accident rates were four times the national average.

In the early 1970s plans to replace the Central Artery began to take form. Engineer Bill Reynolds was the first to propose the idea of building a wider highway in an underground tunnel during a meeting of the Boston Transportation Planning Review. Engineer Fred Salvucci joined Reynolds and began lobbying heavily to replace I-93, and, in 1975, Massachusetts Gov. Michael Dukakis appointed Salvucci state secretary of transportation. When Dukakis lost his bid for reelection in 1978, the I-93 plan was put on hold, while Gov. Edward King instead pushed to extend Interstate Highway 90 (I-90) to Boston’s Logan Airport, another site of heavy congestion.

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Dukakis was elected governor again in 1982, and Salvucci returned to his secretary of transportation post. This time he lobbied for a joint project that would include the I-93 tunnel and the I-90 extension. Planning officially began the same year, as transportation representatives began shoring up local support for the project, which would ultimately turn the elevated six-lane Central Artery into an 8- to 10-lane underground expressway that would eventually become a 10-lane bridge crossing the Charles River. The project would be managed by the Massachusetts Turnpike Authority (MTA) and was codesigned and constructed by the Bechtel Corporation and Parsons Brinckerhoff Quade & Douglas, Inc.

What were some of the Big Dig’s funding and early construction challenges?

A project the size of the Big Dig required federal funding, which was secured in 1987 after the U.S. Senate overrode Pres. Ronald Reagan’s initial veto of the highway bill that contained the funding. Acquiring the necessary private land and environmental mitigation took several years. Construction on the Ted Williams Tunnel—which connects I-90 to Logan Airport beneath Boston Harbor—officially began on December 19, 1991. In order to avoid disrupting the nine rail lines operating above the I-93/I-90 interchange near the tunnel’s southern terminus, this section of the underground expressway was built in an adjacent area before being moved into its final spot with a method called tunnel-jacking. Hundreds of pipes carrying cold brine froze the soil beneath the rail lines and kept it from collapsing while the area was excavated, and the concrete tunnel was forced into place. In submerged sections of construction, steel tubes were lowered into an underwater trench by barges. The Ted Williams Tunnel opened in 1995.

What are the Big Dig’s defining structures?

The slurry walls—strong concrete barriers set in bedrock that held the soil from collapsing into the excavation—for the I-93 tunnel were underway by 1996. Construction was also underway on the Leonard P. Zakim Bunker Hill Memorial Bridge across the Charles River, which would be the widest cable-stayed bridge in the world. The Christian Menn-designed bridge was completed in 2003 and has become an iconic structure. After nearly 15 years of work, the old elevated I-93 expressway was dismantled in 2004. The following year, the new underground section of I-93 was opened.

Was the Big Dig a success?

A number of issues plagued the Big Dig at the end of its construction and after completion. In 2004 it was discovered that the MTA had known for three years of thousands of leaks in the ceilings and walls of the new tunnels. Harbor saltwater continued to corrode steel supports and light fixtures, one of which fell in 2011. In 2006 Milena Del Valle was killed when part of a tunnel ceiling collapsed on her car. Faulty epoxy was blamed for the accident. The same year six men who worked for the Big Dig’s largest concrete supplier were arrested for fraud, as they had allegedly sold the project poor-quality concrete. In response to continuing issues brought on by shoddy construction, the Massachusetts attorney general sued Parsons Brinckerhoff and Bechtel. The firms settled in 2008 and agreed to pay $407 million in restitution.

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The success or failure of the Big Dig is still debated. Its proponents point to the vast tracts of land that were turned into public spaces after the old expressway’s demolition. Most notable among these is the 17-acre (about 7-hectare) Rose Fitzgerald Kennedy Greenway, which occupies the area once overshadowed by I-93. Boston also saw a marked decrease in carbon monoxide emissions as traffic began to move through downtown faster. Hours spent on the refurbished stretch of the expressway dropped by 62 percent, and Bostonians were rewarded with a renewed urban fabric and clearer views. However, critics point to the flawed execution and massive price tag. With interest, the total cost was $24 billion, far more than the original $2.6 billion estimate. Furthermore, in 2008 The Boston Globe reported that while traffic had improved downtown, it had gotten worse outside the city’s core, where new bottlenecks had been created. Public transportation and environmental advocates have wondered whether the money would have been better spent improving and expanding train and bus lines.