Big Dig (Boston, Massachusetts)
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 controlled-access 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.
- 1 Overview
- 2 Historical background
- 3 Early planning
- 4 Obstacles
- 5 Construction phase
- 6 Final phases
- 7 Mitigation projects
- 8 Impact on traffic
- 9 Problems
- 10 See also
- 11 References
- 12 External links
The project was initiated because of chronic congestion on the Central Artery (I-93), an 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 (and swearing motorists)."
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 as of 2006), over $14.6 billion ($8.08 billion in 1982 dollars) had been spent in federal and state tax dollars as of 2006. 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, as of January 2008.
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.
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 their second terms, Michael Dukakis (governor) and Fred Salvucci (secretary of transportation) came up with the strategy of tying the two projects together—thereby combining the project that the business community supported with the project that they and the City of Boston supported.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
In addition to these political and financial difficulties, the project faced several environmental and engineering obstacles.
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. Route 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.
Engineering methods and details
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.
Big Dig, Central Artery / Tunnel Project, Boston, MA, USA
The Big Dig in Boston, Massachusetts, US, is a massive road infrastructure project which was undertaken to improve the flow of traffic, alleviating chronic congestion across Boston and the surrounding commuter areas, and to replace the outmoded elevated Central Artery road that effectively split the city in half, alienating the North End and Waterfront neighbourhoods from the economic life of the city.
The Central Artery / Tunnel Project (CA/T), undertaken by the Massachusetts Turnpike Authority, commenced in 1991. The majority of the project was completed by the middle of 2005 at an estimated cost of $14.625bn (the budget has overrun from the initial estimates of $7.7bn). The Big Dig has proved to be one of the most technically-challenging infrastructure developments ever undertaken in the US and has consisted of two major projects:
- Existing Central Artery, an elevated six-lane highway, replaced by an extended subterranean highway, and a 14-lane two bridge crossing of the Charles River at the northern end
- Extension of the Massachusetts Turnpike (Interstate 90) from its former end, south of downtown Boston, through a tunnel (Ted Williams Tunnel) under South Boston and Boston Harbor to Logan Airport
THE CENTRAL ARTERY
The elevated Central Artery (Interstate 93) was built in 1953 and opened in 1959 with six lanes to comfortably accommodate 75,000 vehicles a day. However, it has regularly carried in excess of 200,000 vehicles a day. As a result, central Boston was subjected to traffic jams for more than ten hours a day (a waste of over $500m per year on fuel burnt by idling engines and late deliveries).
The elevated highway was demolished, freeing up 29 acres for attractive boulevards and parks and been replaced by an eight- to ten-lane underground expressway which leads into a 14-lane, two-bridge crossing at the Charles River.
The road system was designed and constructed to accommodate 245,000 vehicles per day, the projected daily use by 2010.
The northbound Central Artery tunnel started to carry traffic in March 2003, while the southbound lanes were opened in December 2003, allowing for the completion of the largest of the Charles River bridges. Eight lanes were open (four northbound and four southbound) at the end of 2003, with the final two lanes opened in early 2005.
CHARLES RIVER BRIDGES
The larger of the two Charles River bridges, a ten-lane, cable-stayed hybrid bridge, is the widest ever built and the first to use an asymmetrical hybrid design (using steel and concrete). It has been named the Leonard P. Zakim Bunker Hill Bridge. Built at a cost of $100m, it serves the underground Central Artery.
The bridge, providing a spectacular landmark gateway to the city, was opened in stages. Four lanes of I-93 northbound were opened to traffic in March 2003. Four lanes of I-93 southbound were opened in December 2003, while the remaining two lanes opened in early 2005.
With its graceful lines and 270ft towers, the Leonard P. Zakim Bunker Hill Bridge succeeds in linking the past and future of Boston. Swiss bridge designer Christian Menn conceived the bridge to reflect, with its inverted Y-shaped towers, the shape of the Bunker Hill Monument in neighboring Charlestown. The bridge's cables are suggestive of a ship in full sail linking it to East Boston as a center of shipbuilding.
The bridge, at 1,432ft long, emerges from the underground Central Artery near the Fleet Center at Causeway Street, crossing the river to make connections with both I-93 and Route 1. The bridge is designed to carry ten lanes of traffic with eight lanes passing through the legs of the twin towers and two cantilevered on the east side. The cantilever portion, which will accommodate northbound traffic from the Sumner Tunnel and the North End, provides the bridge's unique, asymmetrical design. Girders, floor beams and two planes of cables support the bridge's 745ft-long, 183ft-wide main span. Steel floor beams, which support the main span, are extended out to support the cantilevered lanes.
The Leonard P. Zakim Bunker Hill Bridge is unique. In addition to being the widest cable-stayed bridge in the world, the bridge is the first 'hybrid' cable-stayed bridge in the US, using both steel and concrete in its frame. The main span consists of a steel box girder and steel floor beams, while the back spans contain post-tensioned concrete.
The smaller, four-lane Leverett Circle Connecter Bridge was opened to traffic in October 1999 at a total cost of $22.27m. This 830ft-long bridge connects the Leverett Circle area on the northwestern edge of downtown Boston with points north of the Charles River. Nine box girder sections, the largest in North America, were barged into place and raised into place by cranes or (in the main span) jacks.
The main span length is 380ft and the back span length is 225ft while the width is 76ft. The superstructure consists of single steel box girder, 18ft deep at the piers, 9ft deep at centre span, and a concrete bridge deck. The substructure consists of two water piers and two land bents, cast-in-place and supported on drilled shafts.
INTERSTATE 90 EXTENSION AND HIGHWAY INTERCHANGES
The Massachusetts Turnpike (I-90) Extension opened to traffic in January 2003. The I-90 now runs from Seattle, Washington, to Logan International Airport in East Boston. In Massachusetts, the MassPike now runs 138 miles from the New York border to Route 1A in East Boston.
As a result of the extension, the MassPike runs from its previous terminus at I-93 near South Station to the Fort Point Channel and South Boston before connecting to the Ted Williams Tunnel. Motorists from south and west of Boston have direct access to Logan Airport and Massachusetts' North Shore via I-90 eastbound. This direct, 3.5 mile route to the airport saves drivers as much as 45 minutes off the previous route.
The new I-90 interchange in South Boston also provides direct access to the center of a vital new development area for the Boston seaport, which features the newly opened Massachusetts Convention Center. One of the features of the project has been the relief of cross-town traffic congestion through better traffic distribution and an improved street system.
The construction of the I-90 Extension involved some of the most complicated and challenging engineering on the Central Artery / Tunnel Project. It required tunnel jacking, the construction of a casting basin for immersed tube tunnelling and cut-and-cover tunnel construction.
The project also included five major interchanges to connect the new roads and the existing regional highway system. These are located at Logan Airport, South Boston, Massachusetts Avenue, the Tobin Bridge, and in South Boston where the Central Artery meets the turnpike extension.
At the Southern end of the underground highway the I-90 / I-93 interchange has been rebuilt on six levels to connect with the new Central Artery and the turnpike extension through South Boston. This interchange carries a total of 28 routes to and from Logan Airport and to the East.
By the end of December 2004 over 95% of the Big Dig project was completed. Some 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.
There were many impact-mitigation projects (transit, pedestrian, bicycle, and parks) also remaining but a lot of these were being considered for suspension due to overrun on the budget. The final ramp downtown (exit 20B from I-93 south to Albany Street) opened 13 January 2006.
In 2006, the two Interstate 93 tunnels were dedicated as the Thomas P. O'Neill Jr. Tunnel, after the former Democratic speaker of the House of Representatives from Massachusetts who campaigned for the Big Dig to be funded by the federal government.
TED WILLIAMS TUNNEL
The four-lane Ted Williams Tunnel forms part of the I-90 extension link. The $1.3bn tunnel was named after the legendary Boston Red Sox baseball player. It was the first major target of the Big Dig to be completed, opening to commercial traffic in December 1995.
Providing transport under the harbour, the underwater part of the Ted Williams Tunnel was built using 12 steel sections sunk in a trench to cover the 0.75 mile distance. The tunnel is now fully connected to all its major routes and has the capacity to double cross-harbor traffic.
TRAFFIC MONITORING AND INCIDENT RESPONSE
A highly advanced traffic monitoring and incident response system is in place to ensure the smooth operation of the road infrastructure. The CA/T's Operations Control Center (OCC) has one of the most advanced 'smart highway' systems in the world. The system uses a range of ITS devices. The OCC can monitor all of the traffic in the tunnels, ramps and highways constructed as part of the Big Dig as well as the majority of other roads and tunnels in Boston.
The equipment and facilities used by the OCC include more than 1,400 loop detectors to measure traffic density and identify and project traffic patterns, 430 CCTV cameras, 130 electronic message signboards, 300 lane control signals and carbon monoxide detectors.
The computer system has more than 35,000 data points from which to collect data to compile a detailed picture of traffic events. This enables the OCC to effectively manage traffic flow, incidents, ventilation, security, fire detection and emergency response.
The overall design and construction management for the Big Dig has been provided by a joint venture of Bechtel, Parsons Brinckerhoff, Quade and Douglas. The project included many subcontractors. Major heavy-construction contractors on the project included Jay Cashman, Modern Continental, Gannett Fleming Inc, Obayashi Corporation, Perini Corporation, Peter Kiewit Sons' Incorporated, J.F. White, and the Slattery division of Skanska USA (Modern Continental was awarded the largest value of contracts). Power Fastners provided an epoxy system to hold up concrete roof panels.
The project has incurred criminal arrests, escalating costs, leaks, poor execution and use of substandard materials. The Massachusetts Attorney General demanded that the contractors refund taxpayers $108m for 'shoddy work'.
There were problems with the tunnel as far back as 2001. The Massachusetts Turnpike Authority was aware of many thousands of leaks in the ceiling and wall fissures causing extensive water damage to steel supports and fireproofing systems, and also overloading the drainage systems. An initial $10m contract, signed off as a cost overrun, was used to repair these leaks. Many of the leaks were found to be a result of contractors such as Modern Continental failing to remove gravel and other debris before pouring concrete.
On 15 September 2004, a major leak in the Interstate 93 north tunnel forced the closure of the tunnel while repairs were conducted. This incident also forced the Turnpike Authority to release previous information regarding prior leaks. A follow-up reported on 'extensive' leaks went on to state that the tunnels were riddled with more than 400 serious leaks.
CAUSES OF THE PROBLEMS
In June 2005 Massachusetts State Police were called in to search the offices of Aggregate Industries, the largest concrete supplier for the underground portions of the project. The police obtained evidence of fraudulent records that hid the poor quality of concrete delivered for the highway project. In May 2006, six executives of the company, including its general manager, were arrested and charged with fraud.
In March 2006 it was reported that Massachusetts Attorney General Tom Reilly planned to sue Bechtel/Parsons Brinckerhoff and other companies for over $100m because of poor work on the project. Over 200 complaints were filed by the state of Massachusetts as a result of leaks, cost overruns, quality concerns, and safety violations.
BIG DIG CEILING COLLAPSE
In July 2006 part of the ceiling collapsed in a tunnel segment under South Boston, connecting I-90 to the Ted Williams Tunnel. The collapse killed one person (Milena Del Valle) and contributed to the death of another(her husband). The car was partially crushed under at least four ceiling panels, each weighing 3t. At least 26t of concrete fell from the ceiling of one of the tunnels. A steel tieback that held a 40ft ceiling section over Interstate 90 eastbound had given way.
The accident was investigated by the National Transportation Safety Board and they concluded that the wrong type of epoxy system had been used to hold up concrete ceiling panels. The epoxy holding support anchors holding the panels slowly pulled away and eventually gave way. Power Fasteners Inc was charged with involuntary manslaughter and has agreed to pay the Del Valle family $6m. However, the case is far from over as Power Fastners are claiming that Bechtel/Parsons Brinckerhoff should take a much bigger share of the blame.
The tunnel was closed as work went on to remove about 30 ceiling slabs in a 200ft section where the collapse occurred. The incident raised safety questions and closed part of the project for most of the summer of 2006. In September 2006, one eastbound lane of the connector tunnel was reopened to traffic. Following extensive inspections and repairs, Interstate 90 east and westbound lanes reopened in early January 2007.
BLAME AND REPARATION
In late January 2008 the conclusion of the 'Big Dig' court wrangling finally came to a partial conclusion. The contractors on the project have agreed to pay a sum of over $450m to cover the lawsuit against them for leaks and design flaws and also because of the tunnel roof collapse which cost two lives.
Bechtel/Parsons Brinckerhoff (design and project management) will pay $407m and a number of smaller companies are due to pay a total of $51m between them. If there is any future problem (structural defect) then the state can claim up to $100m more from Bechtel/Parsons Brinckerhoff but this would be decided by arbitration.