The Big Dig is the unofficial name of the Central Artery/Tunnel Project (CA/T), a megaproject that rerouted the Central Artery (Interstate 93), the chief highway through the heart of Boston, Massachusetts, into a 3.5 mile (5.6 km) tunnel under the city. The project also included the construction of the Ted Williams Tunnel (extending Interstate 90 to Logan International Airport), the Leonard P. Zakim Bunker Hill Memorial Bridge over the Charles River, and the Rose Kennedy Greenway in the space vacated by the previous I-93 elevated roadway. Initially, the plan was also to include a rail connection between Boston's two major train terminals. The project concluded on December 31, 2007, when the partnership between program manager Bechtel/Parsons Brinckerhoff and the Massachusetts Turnpike Authority ended.
In 1959, the 1.5-mile-long (2.4 km) road section carried approximately 75,000 vehicles a day, but by the 1990s, this had grown to 190,000 vehicles a day. Traffic jams of 16 hours were predicted for 2010.
The project was officially handed over to the Massachusetts Turnpike Authority at the end of 2007.
The Big Dig has been the most expensive highway project in the U.S. Although the project was estimated at $2.8 billion in 1985 (in 1982 dollars, US$6.0 billion adjusted for inflation ), over $14.6 billion ($8.08 billion in 1982 dollars) had been spent in federal and state tax dollars . A July 17, 2008 article in The Boston Globe stated, "In all, the project will cost an additional $7 billion in interest, bringing the total to a staggering $22 billion, according to a Globe review of hundreds of pages of state documents. It will not be paid off until 2038. At the beginning of the project, Congressman Barney Frank asked, "Rather than lower the expressway, wouldn't it be cheaper to raise the city?" The project has incurred criminal arrests, escalating costs, death, leaks, and charges of poor execution and use of substandard materials. The Massachusetts Attorney General is demanding contractors refund taxpayers $108 million for "shoddy work". On January 23, 2008, it was reported that Bechtel/Parsons Brinckerhoff, the consortium that oversaw the project, would pay $407 million in restitution for its poor oversight of subcontractors (some of whom committed outright fraud), as well as primary responsibility in the death of a motorist. However, despite admitting to poor oversight and negligence as part of the settlement, the firm is not barred from bidding for future government contracts. Several smaller companies agreed to pay a combined sum of approximately $51 million.
The Massachusetts Turnpike Authority (MTA), which had little experience in managing an undertaking of the scope and magnitude of the CA/T Project, hired a joint venture of Bechtel/Parsons Brinckerhoff 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 Bechtel/Parsons employees in an integrated project organization. This was intended to make management more efficient, but it hindered MTA's ability to independently oversee Bechtel/Parsons Brinckerhoff because MTA and Bechtel/Parsons Brinckerhoff had effectively become partners in the project.
Litigation against Bechtel and others in the death of a motorist remains pending, .
Boston's historically tangled streets were laid out long before the advent of the automobile. By the mid-20th century, car traffic in the inner city was extremely congested, with north-south trips especially so. Commissioner of Public Works William Callahan advanced plans for an elevated expressway which eventually was constructed (1951-59) between the downtown area and the waterfront. The Central Artery (known officially as the John F. Fitzgerald Expressway) displaced thousands of residents and businesses and physically divided the historical connection between the downtown and market areas and the waterfront. Governor John Volpe interceded in the 1950s to send the last section of the Central Artery underground, through the Dewey Square (or "South Station") Tunnel, but while traffic moved somewhat better the other problems remained.
Built before strict federal Interstate Highway standards were developed during the Eisenhower administration, the expressway was plagued by tight turns, an excessive number of entrances and exits, entrance ramps without merge lanes, and continually escalating vehicular loads. Local businesses again wanted relief, historians sought a reuniting of the waterfront with the city, and nearby residents desired removal of this "Green Monster". (Its matte green paint prompted Thomas Menino to call it Boston's "other Green Monster". The original Green Monster is Fenway Park's left field wall.) MIT engineers Bill Reynolds and future state Secretary of Transportation Frederick P. Salvucci envisioned moving the whole expressway underground.
Planning for the Big Dig as a project officially began in 1982, with environmental impact studies starting in 1983. After years of extensive lobbying for federal dollars, a 1987 public works bill appropriating funding for the Big Dig was passed by U.S. Congress, but it was subsequently vetoed by President Ronald Reagan as being too expensive. When Congress overrode his veto, the project had its green light and ground was first broken in 1991.
The downtown area through which the tunnels were to be dug was largely landfill, and included existing subway lines as well as innumerable pipes and utility lines that would have to be replaced or moved. Tunnel workers encountered many unexpected geological and archaeological barriers, ranging from glacial debris to foundations of buried houses and a number of sunken ships lying within the reclaimed land.
The project received approval from state environmental agencies in 1991, after satisfying concerns including release of toxins by the excavation and the possibility of disrupting the homes of millions of rats, causing them to roam the streets of Boston in search of new housing. By the time the federal environmental clearances were delivered in 1994, the process had taken some seven years, during which time inflation greatly increased the project's original cost estimates.
Reworking such a busy corridor without seriously restricting traffic flow required a number of state-of-the-art construction techniques. Because the old elevated highway (which remained in operation throughout the construction process) rested on pylons located throughout the designated dig area, engineers first utilized slurry wall techniques to create 120 ft.-deep concrete walls upon which the highway could rest. These concrete walls also stabilized the sides of the site, preventing cave-ins during the excavation process.
The multilane interstates also had to pass under South Station's 7 tracks which carried over 40,000 commuters and 400 trains per day. In order to avoid multiple relocations of the train lines while the tunnelling advanced, as had been initially planned, a specially designed jack was constructed in order to support the ground and tracks to allow the excavation to take place below. Ground freezing was also implemented in order to help stabilize the surrounding ground as the tunnel was excavated. This was the largest tunnelling project undertaken beneath railway lines anywhere in the world. The ground freezing enabled safer, more efficient excavation, and also assisted in environmental issues, as less contaminated fill needed to be exported than if a traditional cut and cover method had been applied.
Other challenges included an existing subway tunnel crossing the path of the underground highway. In order to build slurry walls past this tunnel, it was necessary to dig beneath the tunnel and build an underground concrete bridge to support the tunnel's weight.
The project was managed by the Massachusetts Turnpike Authority, with design and construction supervised by a joint venture of Bechtel Corporation and Parsons Brinckerhoff. Due to the enormous size of the project—too large for any company to undertake alone—the design and construction of the Big Dig were broken up into dozens of smaller subprojects with well-defined interfaces between contractors. Major heavy-construction contractors on the project included Jay Cashman, Modern Continental, Obayashi Corporation, Perini Corporation, Peter Kiewit Sons' Incorporated, J.F. White, and the Slattery division of Skanska USA. (Of those, Modern Continental was awarded the greatest gross value of contracts, joint ventures included.)
The nature of the Charles River crossing had been a source of major controversy throughout the design phase of the project. Many environmental advocates preferred a river crossing entirely in tunnels, but this, along with 27 other plans, was rejected as too costly. Finally, with a deadline looming to begin construction on a separate project that would connect the Tobin Bridge to the Charles River crossing, Salvucci overrode the objections and chose a variant of the plan known as "Scheme Z". This plan was considered to be reasonably cost-effective, but had the drawback of requiring highway ramps stacked up as high as 100 feet (30 m) immediately adjacent to the Charles River. The city of Cambridge objected to the visual impact of the chosen Charles River crossing design. It sued to revoke the project's environmental certificate and forced the project to redesign the river crossing again.
Swiss Engineer Christian Menn took over the design of the bridge. He suggested a sleek, modern, cable-stayed bridge that would carry 10 lanes of traffic. The plan was accepted and construction began on the Leonard P. Zakim Bunker Hill Memorial Bridge. The bridge employed an asymmetrical design and a hybrid of steel and concrete was used to construct it. It was the first bridge in the country to employ this method and it is the widest cable-stayed bridge in the world.
Meanwhile, construction continued on the Tobin Bridge approach. By the time all parties agreed on the I-93 design, construction of the Tobin connector (today known as the "City Square Tunnel" for a Charlestown area it bypasses) was far along, significantly adding to the cost of constructing the U.S. 1 interchange and retrofitting the tunnel.
Boston blue clay and other soils extracted from the path of the tunnel were used to cap many local landfills, fill in the Granite Rail Quarry in Quincy, and restore the surface of Spectacle Island in the Boston Harbor Islands National Recreation Area.
The Leonard P. Zakim Bunker Hill Memorial Bridge, designed by Swiss designer Christian Menn, is the terminus of the project, connecting the underground highway with I-93 and U.S. 1. The distinctive cable-stayed bridge is supported by two forked towers connected to the span by cables and girders.
The Storrow Drive Connector, a companion bridge to the Zakim, began carrying traffic from I-93 to Storrow Drive in 1999. The project had been under consideration for years, but was opposed by the wealthy residents of the Beacon Hill neighborhood. However, it finally was accepted because it would funnel traffic bound for Storrow Drive and downtown Boston away from the mainline roadway. The Connector ultimately used a pair of ramps that had been constructed for Interstate 695, enabling the mainline I-93 to carry more traffic that would have used I-695 under the original Master Plan.
When construction began, the project cost, including the Charles River crossing, was estimated at $5.8 billion. Eventual cost overruns were so high that the chairman of the Massachusetts Turnpike Authority, James Kerasiotes, was fired in 2000. His replacement had to commit to an $8.55 billion cap on federal contributions. Total expenses eventually passed $15 billion. Interest brought this cost to $21.93 billion.
Several unusual engineering challenges arose during the project, requiring unusual solutions and methods to address them.
At the beginning of the project, engineers had to figure out the safest way to build the tunnel without endangering the existing elevated highway above. Eventually, they created horizontal braces as wide as the tunnel, then cut away the elevated highway's struts, and lowered it onto the new braces.
On January 17, 2003, the opening ceremony was held for the I-90 Connector Tunnel, extending the Massachusetts Turnpike (Interstate 90) east into the Ted Williams Tunnel, and onwards to Logan Airport. The Ted Williams tunnel had been completed and in limited use for commercial traffic and high-occupancy vehicles since late 1995. The westbound lanes opened on the afternoon of January 18 and the eastbound lanes on January 19.
The next phase, moving the elevated Interstate 93 underground, was completed in two stages: northbound lanes opened in March 2003 and southbound lanes (in a temporary configuration) on December 20, 2003. A tunnel underneath Leverett Circle connecting eastbound Storrow Drive to I-93 North and the Tobin Bridge opened December 19, 2004, easing congestion at the circle. All southbound lanes of I-93 opened to traffic on March 5, 2005, including the left lane of the Zakim Bridge, and all of the refurbished Dewey Square Tunnel.
By the end of December 2004, 95% of the Big Dig was completed. Major construction remained on the surface, including construction of final ramp configurations in the North End and in the South Bay interchange, and reconstruction of the surface streets.
In 2006, the two Interstate 93 tunnels were dedicated as the Thomas "Tip" O'Neill Tunnel, after the former Democratic speaker of the House of Representatives from Massachusetts who pushed to have the Big Dig funded by the federal government.
Many environmental impact mitigation projects (transit, pedestrian, bicycle, and parks) also remain. Although these were legal requirements for approval of the environmental impact statement, many are not funded due to the massive cost overruns on the highway portion of the project.
Prior to construction of the Big Dig, the Central Artery carried not only north-south traffic but much east-west traffic, a major cause of its all-day congestion. The only direct access to Boston's Logan Airport from downtown was through the paired Callahan and Sumner tunnels under Boston Harbor. To reach these tunnels, traffic on the major highways from west of Boston – the Massachusetts Turnpike and Storrow Drive – traveled on portions of the Central Artery. Getting between the Central Artery and the tunnels also involved short stretches on city streets, increasing local congestion and causing backups on the highway.
The Big Dig untangled this commingled traffic. While only one net lane in each direction was added to the north-south I-93, several new east-west lanes became available. East-west traffic on the Massachusetts Turnpike/I-90 now proceeds directly through the Ted Williams Tunnel to Logan Airport and Route 1A beyond. Traffic between Storrow Drive and the Callahan and Sumner Tunnels still uses a short portion of I-93, but additional lanes and direct connections are provided for this traffic.
The result was a 62% reduction in vehicle hours of travel on I-93, the airport tunnels, and the connection from Storrow Drive, from an average 38,200 hours per day before construction (1994-1995) to 14,800 hours per day in 2004-2005, after the project was largely complete.(Table 3-6) The savings for travelers was estimated at $166 million annually in the same 2004-2005 time frame. Travel times on the Central Artery northbound during the afternoon peak hour were reduced 85.6%.
On September 15, 2004, a major leak in the Interstate 93 north tunnel forced the closure of the tunnel while repairs were conducted. This also forced the Turnpike Authority to release information regarding its non-disclosure of prior leaks. A follow-up reported on "extensive" leaks that were more severe than state authorities had previously acknowledged. The report went on to state that the $14.6 billion tunnel system was riddled with more than 400 leaks. A Boston Globe report, however, countered that by stating there were nearly 700 leaks in a single 1,000-foot section of tunnel beneath South Station. Turnpike officials also stated that the number of leaks being investigated was down from 1,000 to 500.
On March 19, 2006, the International Herald Tribune reported that Massachusetts Attorney General Tom Reilly planned to sue Bechtel/Parsons Brinckerhoff and other companies because of poor work on the project. Over 200 complaints have been filed by the state of Massachusetts as a result of leaks, cost overruns, quality concerns, and safety violations. In total, the state is seeking approximately $100 million from the contractors ($1 for every $141 spent).
A fatal accident raised safety questions and closed part of the project for most of the summer of 2006. On July 10, 2006, a concrete ceiling panel weighing 3 tons (2.7 t) and measuring 20 by 40 ft (6.1 by 12.2 m) fell on a car traveling on the two-lane ramp connecting northbound I-93 to eastbound I-90 in South Boston, killing Milena Del Valle, who was a passenger, and injuring her husband, Angel Del Valle, who was driving. The collapse also contributed to the death of another person, a heart attack victim who died en route to a hospital when his ambulance was caught in a resulting traffic jam two weeks after the collapse. On September 1, 2006, one eastbound lane of the connector tunnel was re-opened to traffic.
Following extensive inspections and repairs, Interstate 90 east and west bound lanes reopened in early January 2007. The final piece of the road network, a high occupancy vehicle lane connecting Interstate 93 north to the Ted Williams Tunnel, was reopened on June 1, 2007.
On July 10, 2007 after a lengthy investigation, the National Transportation Safety Board found that epoxy glue used to hold the roof in place during construction was not appropriate for long term bonding. This was determined to be the cause of the roof collapse. The Power-Fast Epoxy Adhesive from Powers Fasteners used in the installation was designed for short term loading, such as wind or earthquake loads, not long term loading such as the weight of a panel.
Powers Fasteners revised their product specifications on May 15, 2007 to increase the safety factor from 4 to 10 for any of their epoxy products which are intended for use in overhead applications. The safety factor on Power-Fast Epoxy in particular was increased from 4 to 16.
On December 24, 2007, the Del Valle family announced they had reached a settlement with Power Fasteners, in which they would be paid $6 million. Power Fasteners is still facing a charge of manslaughter.