The Central Artery/Tunnel Project (CA/T), known unofficially as the
Big Dig, was a megaproject in
Boston that rerouted the Central Artery
of Interstate 93, the chief highway through the heart of the city,
into the 1.5-mile (2.4 km) Thomas P. O'Neill Jr. Tunnel. The
project also included the construction of the Ted Williams Tunnel
Interstate 90 to Logan International Airport), the Leonard
P. Zakim Bunker Hill Memorial Bridge over the Charles River, and the
Rose Kennedy Greenway
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. Planning began
in 1982; the construction work was carried out between 1991 and 2006;
and the project concluded on December 31, 2007 when the partnership
between the program manager and the
Massachusetts Turnpike Authority
Big Dig was the most expensive highway project in the US, and was
plagued by cost overruns, delays, leaks, design flaws, charges of poor
execution and use of substandard materials, criminal arrests,
and one death. The project was originally scheduled to be completed
in 1998 at an estimated cost of $2.8 billion (in 1982 dollars,
US$6.0 billion adjusted for inflation as of 2006[update]). However,
the project was completed in December 2007 at a cost of over $14.6
billion ($8.08 billion in 1982 dollars, meaning a cost overrun of
about 190%) as of 2006[update]. The
Boston Globe estimated that
the project will ultimately cost $22 billion, including interest, and
that it would not be paid off until 2038. As a result of a death,
leaks, and other design flaws,
Bechtel and Parsons Brinckerhoff—the
consortium that oversaw the project- agreed to pay $407 million in
restitution and several smaller companies agreed to pay a combined sum
of approximately $51 million.
Rose Fitzgerald Kennedy Greenway
Rose Fitzgerald Kennedy Greenway is a roughly 1.5-mile-long
(2.4 km) series of parks and public spaces, which are the
final part of the
Big Dig after
Interstate 93 was put underground. The
Greenway was named in honor of
Kennedy family matriarch Rose
Fitzgerald Kennedy, and was officially dedicated on July 26, 2004.
1.2 Cancellation of the Inner Belt project
1.3 Mixing of traffic
1.4 Mass transit
2 Early planning
4 Construction phase
4.1 Engineering methods and details
5 Final phases
6 Coordinated projects
6.1 Surface treatments
6.2 Public art
7 Impact on traffic
8 Operations Control Center (OCC)
9.1 "Thousands of leaks"
9.2 Substandard materials
9.3 Fatal ceiling collapse
9.5 Lighting fixtures
10 See also
12 External links
Traffic on the old, elevated Central Artery at mid-day in 2003
This project was developed in response to traffic congestion on
Boston's historically tangled streets which were laid out long before
the advent of the automobile. As early as 1930 the city's Planning
Board recommended a raised express highway running north-south through
the downtown district in order to draw traffic off the city
streets. Commissioner of Public Works William Callahan promoted
plans for an elevated expressway which eventually was constructed
between the downtown area and the waterfront. Governor John Volpe
interceded in the 1950s to change the design of the last section of
the Central Artery putting it underground through the Dewey Square
Tunnel. While traffic moved somewhat better, the other problems
remained. There was 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
The expressway had tight turns, an excessive number of entrances and
exits, entrance ramps without merge lanes, and as the decades passed,
had continually escalating vehicular traffic that was well beyond its
design capacity. Local businesses again wanted relief, city leaders
sought a reuniting of the waterfront with the city, and nearby
residents desired removal of the matte green-painted elevated road
Thomas Menino called Boston's "other Green Monster".
MIT engineers Bill Reynolds and (eventual state Secretary of
Frederick P. Salvucci
Frederick P. Salvucci envisioned moving the whole
Cancellation of the Inner Belt project
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Zakim Bunker Hill Bridge
Zakim Bunker Hill Bridge over the
Charles River under construction,
looking north. The old elevated Central Artery crossing is to the
Another important motivation for the final form of the
Big Dig was the
abandonment of the Massachusetts Department of Public Works' intended
expressway system through and around Boston. The Central Artery, as
part of Mass. DPW's Master Plan of 1948, was originally planned to be
Boston stretch of Interstate 95, and was signed as such;
a bypass road called the Inner Belt, was subsequently renamed
Interstate 695. (The law establishing the Interstate highway system
was enacted in 1956.) The
Inner Belt District
Inner Belt District was to pass to the west
of the downtown core, through the neighborhood of Roxbury and the
cities of Brookline, Cambridge, and Somerville. Earlier controversies
over impact of the
Boston extension of the Massachusetts Turnpike,
particularly on the heavily populated neighborhood of Brighton, and
the additional large amount of housing that would have had to be
destroyed led to massive community opposition to both the Inner Belt
Boston section of I-95.
Building demolition and land clearances for I-95 through the
neighborhoods of Roxbury, Jamaica Plain, and
Roslindale led to
secession threats by Hyde Park, Boston's youngest and southernmost
neighborhood. By 1972, with only a minimum of work done on the I-95
right of way and none on the potentially massively disruptive Inner
Francis Sargent put a moratorium on highway
construction within the MA-128 corridor, except for the final short
stretch of Interstate 93. In 1974, the remainder of the Master Plan
was canceled, leaving
Boston with a severely overstressed expressway
system for the existing traffic.
With ever-increasing traffic volumes funneled onto I-93 alone, the
Central Artery became chronically gridlocked. The Sargent moratorium
led to the rerouting of I-95 away from
Boston around the MA-128
beltway and the conversion of the cleared land in the southern part of
the city into the Southwest Corridor linear park, as well as a new
right-of-way for the Orange Line subway and Amtrak. Parts of the
planned I-695 right-of-way remain unused and under consideration for
future mass-transit projects.
The original 1948 Master Plan included a Third Harbor Tunnel plan that
was hugely controversial in its own right, because it would have
Maverick Square area of East Boston. It was never built.
Mixing of traffic
A major reason for the all-day congestion was that the Central Artery
carried not only north–south traffic, but much east–west traffic
as well. Boston's
Logan Airport lies across
Boston Harbor in East
Boston, and before the
Big Dig the only access from downtown was
through the paired Callahan and Sumner tunnels. Traffic on the major
highways from west of Boston—the
Massachusetts Turnpike and Storrow
Drive—mostly traveled on portions of the Central Artery to reach
these tunnels. Getting between the Central Artery and the tunnels
involved short diversions onto city streets, increasing local
A number of public transportation projects were included as part of an
environmental mitigation for the Big Dig. The most expensive was the
building of the Phase II Silver Line tunnel under Fort Point Channel,
done in coordination with
Big Dig construction. Silver Line buses now
use this tunnel and the
Ted Williams Tunnel
Ted Williams Tunnel to link
South Station and
As of 2015[update], promised projects to extend the Green Line beyond
Lechmere, to connect the Red and Blue subway lines, and to restore the
Green Line streetcar service to the Arborway in
Jamaica Plain have not
been completed. Construction of the extension beyond Lechmere has
begun. The Red and Blue subway line connection underwent initial
design, but no funding has been designated for the project. The
Arborway Line restoration has been abandoned, following a final court
decision in 2011.
Big Dig plan also included the North-South Rail Link,
which would have connected North and South Stations (the major
passenger train stations in Boston), but this aspect of the project
was ultimately dropped by the state transportation administration
early in the Dukakis administration. Negotiations with the federal
government had led to an agreement to widen some of the lanes in the
new harbor tunnel, and accommodating these would require the tunnel to
be deeper and mechanically-vented; this left no room for the rail
lines, and having diesel trains (then in use) passing through the
tunnel would have substantially increased the cost of the ventilation
The project was conceived in the 1970s by the
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
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 the US Congress,
but it was vetoed by President
Ronald Reagan for being too expensive.
When Congress overrode the veto, the project had its green light and
ground was first broken in 1991.
In 1997, the state legislature created the Metropolitan
and transferred responsibility for the Central Artery and Tunnel
"CA/T" Project from the Massachusetts
Highway Department and the
Massachusetts Governor's Office to the Massachusetts Turnpike
Authority (MTA). The MTA, which had little experience in
managing an undertaking of the scope and magnitude of the CA/T
Project, hired a joint venture 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 joint venture employees in an integrated
project organization. This was intended to make management more
efficient, but it hindered MTA's ability to independently oversee
project activities because MTA and the joint venture had effectively
become partners in the project.
In addition to 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 Red Line and Blue Line subway tunnels 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
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
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-foot-deep (37 m) concrete walls
upon which the highway could rest. These concrete walls also
stabilized the sides of the site, preventing cave-ins during the
continued excavation process.
The multi-lane interstate highway also had to pass under South
Station's seven railway tracks, which carried over 40,000 commuters
and 400 trains per day. To avoid multiple relocations of train lines
while the tunneling advanced, as had been initially planned, a
specially designed jack was constructed to support the ground and
tracks to allow the excavation to take place below. Construction crews
also used ground freezing (an artificial induction of permafrost) to
help stabilize surrounding ground as they excavated the tunnel. This
was the largest tunneling 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 existing subway tunnels crossing the path of
the underground highway. To build slurry walls past these tunnels, it
was necessary to dig beneath the tunnels and to build an underground
concrete bridge to support the tunnels' weight, without interrupting
Construction sites of the "Big Dig"
The project was managed by the
Massachusetts Turnpike Authority, with
Big Dig and the Turnpike's
Boston Extension from the 1960s being
financially and legally joined by the legislature as the Metropolitan
Highway System. Design and construction was supervised by a joint
Bechtel Corporation and Parsons Brinckerhoff. Because of
the enormous size of the project—too large for any company to
undertake alone—the design and construction of the
Big Dig was
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
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. The city sued to revoke the project's
environmental certificate and forced the project planners to redesign
the river crossing again.
Leonard P. Zakim Bridge
Christian Menn took over the design of the bridge. He
suggested a cradle cable-stayed bridge that would carry ten 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. The distinctive bridge is supported by two forked towers
connected to the span by cables and girders. It was the first bridge
in the country to employ this method and it was, at the time, the
widest cable-stayed bridge in the world, having since been
surpassed by the Eastern span replacement of the San
Francisco–Oakland Bay Bridge.
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 US 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.
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
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. The total expenses
eventually passed $15 billion. Interest brought this cost to $21.93
Engineering methods and details
Temporary supports hold up elevated Central Artery during
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.
Interstate 93 Tunnel
On January 18, 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
International Airport. The Ted Williams tunnel had been completed and
was 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.
The final ramp downtown — exit 20B from I-93 south to Albany Street
— opened January 13, 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 pushed to have the Big Dig
funded by the federal government.
The Commonwealth of Massachusetts was required under the Federal Clean
Air Act to mitigate air pollution generated by the highway
improvements. Secretary of Transportation
Fred Salvucci signed an
agreement with the Conservation Law Foundation in 1990 enumerating 14
specific projects the state agreed to build. This list was affirmed in
a 1992 lawsuit settlement.
Projects which have been completed include:
Restoration of three Old Colony Commuter Rail lines
Expansion of Framingham Line to serve Worcester full-time
Restoration of the Newburyport/Rockport Line
Six-car trains on the MBTA Blue Line, requiring platform lengthening,
station modernization, and all new train cars
MBTA Silver Line
MBTA Silver Line service to the South
1,000 new commuter parking spaces
As of 2014, several mitigation projects were incomplete:
Green Line Extension
Green Line Extension to Somerville and Medford
Fairmount Line improvements
Design of the Red-Blue Connector at Charles Street (under petition to
remove from list)
Some projects, such as restoration of Green Line "E" Arborway service,
were removed from the list of mitigation projects and replaced with
other projects with similar air-quality improvements.
Some surface treatments, that were part of the original project plan,
were dropped due to the massive cost overruns on the highway portion
of the project. For example, the North Point Park was
created as part of the project, but it ended without constructing
pedestrian bridges to neighboring parks. The bridges were later funded
by the American Recovery and Reinvestment Act of 2009.
While not a legally mandated requirement, public art was part of the
urban design planning process (and later design development work)
through the Artery Arts Program. The intent of the program was to
integrate public art into highway infrastructure (retaining walls,
fences, and lighting) and the essential elements of the pedestrian
environment (walkways, park landscape elements, and bridges). As
overall project costs increased, the Artery Arts Program was seen as a
potential liability, even though there was support and interest from
the public and professional arts organizations in the area.
At the beginning of the highway design process, a temporary arts
program was initiated, and over 50 proposals were selected. However,
development began on only a few projects before funding for the
program was cut. Permanent public art that was funded includes: super
graphic text and facades of former West End houses cast into the
concrete elevated highway abutment support walls near
North Station by
artist Sheila Levrant de Bretteville; Harbor Fog, a sensor-activated
mist, light and sound sculptural environment by artist Ross Miller in
parcel 17; an historical sculpture celebrating the 18th and 19th
century shipbuilding industry and a bust of shipbuilder Donald McKay
in East Boston; blue interior lighting of the Zakim Bridge; and the
Miller's River Littoral Way walkway and lighting under the loop ramps
north of the Charles River.
Extensive landscape planting, as well as a maintenance program to
support the plantings, was requested by many community members during
Impact on traffic
Traffic exiting the
Thomas P. O'Neill Jr. Tunnel
Thomas P. O'Neill Jr. Tunnel onto the Zakim
Big Dig untangled the co-mingled traffic from the Massachusetts
Turnpike and the Sumner and Callahan Tunnels. 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. 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
Boston Globe report asserted that waiting time for the majority
of trips actually increased as a result of demand induced by the
increased road capacity. Because more drivers were opting to use the
new roads, traffic bottlenecks were only pushed outward from the city,
not reduced or eliminated (although some trips are now faster). The
report states, "Ultimately, many motorists going to and from the
suburbs at peak rush hours are spending more time stuck in traffic,
not less." The Globe also asserted that their analysis provides a
fuller picture of the traffic situation than a state-commissioned
study done two years earlier, in which the
Big Dig was credited with
helping to save at least $167 million a year by increasing economic
productivity and decreasing motor vehicle operating costs. That study
did not look at highways outside the
Big Dig construction area and did
not take into account new congestion elsewhere.
Operations Control Center (OCC)
This section needs expansion. You can help by adding to it. (April
As part of the project, an elaborate Operations Control Center (OCC)
control room was constructed in South Boston. Staffed on a "24/7/365"
basis, this center monitors and reports on traffic congestion, and
responds to emergencies. Continuous video surveillance is provided by
hundreds of cameras, and thousands of sensors monitor traffic speed
and density, air quality, water levels, temperatures, equipment
status, and other conditions inside the tunnel. The OCC can activate
emergency ventilation fans, change electronic display signs, and
dispatch service crews when necessary.
"Thousands of leaks"
As far back as 2001, Turnpike Authority officials and contractors knew
of thousands of leaks in ceiling and wall fissures, extensive water
damage to steel supports and fireproofing systems, and overloaded
drainage systems. A $10 million contract, signed off as a cost
overrun, was used to repair these leaks. Many of the leaks were a
Modern Continental and other subcontractors failing to
remove gravel and other debris before pouring concrete. This
information was not made public; engineers at MIT (volunteer students
and professors) performed several experiments and found serious
problems with the tunnel.
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
report, however, countered that by stating there were nearly 700 leaks
in a single 1,000-foot (300 m) section of tunnel beneath South
Station. Turnpike officials also stated that the number of leaks being
investigated was down from 1,000 to 500.
The problem of leaks is further aggravated by the fact that many of
them involve corrosive salt water. This is caused by the proximity of
Boston Harbor and the Atlantic Ocean, causing a mix of salt and fresh
water leaks in the tunnel. The situation is made worse by road salt
spread in the tunnel to melt ice during freezing weather, or brought
in by vehicles passing through. Salt water and salt spray are
well-known issues that must be dealt with in any marine environment.
It has been reported that "hundreds of thousands of gallons of salt
water are pumped out monthly" in the Big Dig, and a map has been
prepared showing "hot spots" where water leakage is especially
serious. Salt-accelerated corrosion has caused ceiling light
fixtures to fail (see below), but can also cause rapid deterioration
of embedded rebar and other structural steel reinforcements holding
the tunnel walls and ceiling in place.
The much larger than expected volume of water that must be
continuously pumped consumes a correspondingly larger amount of
electrical power, and will cause the pumps to wear out much sooner
than originally estimated.
This section needs to be updated. Please update this article to
reflect recent events or newly available information.
Last update: what happened after the arrests and charges (December
Massachusetts State Police
Massachusetts State Police searched the offices of Aggregate
Industries, the largest concrete supplier for the underground portions
of the project, in June 2005. They seized evidence that Aggregate
delivered concrete that did not meet contract specifications. In March
2006 Massachusetts Attorney General Tom Reilly announced plans to sue
project contractors and others 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. In total, the state has sought approximately $100 million
from the contractors ($1 for every $141 spent).
In May 2006, six employees of the company were arrested and charged
with conspiracy to defraud the United States. In July 2007, Aggregate
Industries settled the case with an agreement to pay $50 million. $42
million of the settlement went to civil cases and $8 million was paid
in criminal fines. The company will provide $75 million in insurance
for maintenance as well as pay $500,000 toward routine checks on areas
suspected to contain substandard concrete.
Fatal ceiling collapse
Big Dig ceiling collapse
Boston traffic crawls over a closed
Ted Williams Tunnel
Ted Williams Tunnel entrance in
Boston during rush hour on July 11, 2006, the day after the collapse.
A fatal accident raised safety questions and closed part of the
project for most of the summer of 2006. On July 10, 2006, concrete
ceiling panels and debris weighing 26 short tons (24 tonnes) 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.
Immediately following the fatal ceiling collapse, Governor Mitt Romney
ordered a "stem-to-stern" safety audit conducted by the Illinois
engineering firm of
Wiss, Janney, Elstner Associates, Inc.
Wiss, Janney, Elstner Associates, Inc. to look for
additional areas of risk. Said Romney: "We simply cannot live in a
setting where a project of this scale has the potential of threatening
human life, as has already been seen". The collapse and closure of
the tunnel greatly snarled traffic in the city. The resulting traffic
jams are cited as contributing to the death of another person, a heart
attack victim who died en route to
Boston Medical Center when his
ambulance was caught in one such 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
westbound 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, 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.
Epoxy Adhesive 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, the makers of the adhesive, revised their product
specifications on May 15, 2007, to increase the safety factor from 4
to 10 for all of their epoxy products intended for use in overhead
applications. The safety factor on Power-Fast
Epoxy was increased from
4 to 16. On December 24, 2007, the Del Valle family announced they
had reached a settlement with Powers Fasteners that would pay the
family $6 million. In December 2008, Power Fasteners agreed to pay
$16 million to the state to settle manslaughter charges.
Public safety workers have called the walkway safety handrails in the
Big Dig tunnels "ginsu guardrails", because the squared-off edges of
the support posts have caused mutilations and deaths of passengers
ejected from crashed vehicles. After an eighth reported death
involving the safety handrails,
MassDOT officials announced plans to
cover or remove the allegedly dangerous fixtures, but only near curves
or exit ramps. This partial removal of hazards has been criticized
by a safety specialist, who suggests that the handrails are just as
dangerous in straight sections of the tunnel.
In March 2011, it became known that senior
MassDOT officials had
failed to disclose an issue with the lighting fixtures in the O'Neill
tunnel. In early February 2011, a maintenance crew found a fixture
lying in the middle travel lane in the northbound tunnel. Assuming
it to be simple road debris, the maintenance team picked it up and
brought it back to its home facility. The next day, a supervisor
passing through the yard realized that the 120 lb (54 kg)
fixture was not road debris but was in fact one of the fixtures used
to light the tunnel itself. Further investigation revealed that the
fixture's mounting apparatus had failed, due to galvanic corrosion of
incompatible metals, caused by having aluminum in direct contact with
stainless steel, in the presence of salt water. The
electrochemical potential difference between stainless steel and
aluminum is in the range of 0.5 to 1.0V, depending on the exact alloys
involved, and can cause considerable corrosion within months under
After the discovery of the reason why the fixture had failed, a
comprehensive inspection of the other fixtures in the tunnel revealed
that numerous other fixtures were also in the same state of
deterioration. Some of the worst fixtures were temporarily shored
up with plastic ties. Moving forward with temporary repairs,
members of the
MassDOT administration team decided not to let the news
of the systemic failure and repair of the fixtures be released to the
public or to Governor Deval Patrick's administration.
As of April 2012[update], it appeared that all of the 25,000
light fixtures would have to be replaced, at an estimated cost of $54
million. The replacement work is mostly done at night, and
requires lane closures or occasional closing of the entire tunnel for
safety, and was estimated to take up to 2 years to complete. As of
April 2016[update], replacement of the light fixtures is still
Massachusetts Bay Transportation Authority
Vincent Zarrilli – critic of the
Big Dig who proposed the Boston
Alaskan Way Viaduct replacement tunnel
Alaskan Way Viaduct replacement tunnel – similar project in Seattle,
Carmel Tunnels – similar project in Haifa, Israel
Central-Wan Chai Bypass
Central-Wan Chai Bypass – similar project in the areas of Central,
Wan Chai and Causeway Bay, within Victoria City, Hong Kong
Cross City Tunnel
Cross City Tunnel – similar project in Sydney, New South Wales,
Dublin Port Tunnel
Dublin Port Tunnel – similar project on a smaller scale in Dublin,
Gardiner Expressway – an elevated freeway in
Toronto with similar
Autopista de Circunvalación M-30, Túneles de la M-30 (es) and
Parque Madrid Río (es) – similar project along the banks of
Manzanares River, Madrid, Spain
Blanka tunnel complex
Blanka tunnel complex – similar project in Prague, Czech Republic
and the longest city tunnel in Europe (6.4 km / 4.0 mi)
Yamate Tunnel – similar project on a larger scale in Tokyo, Japan
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Epoxy company hit with Big Dig
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Wikimedia Commons has media related to Big Dig.
Boston CA/T Project History at MIT Rotch Library
PBS.org – Central Artery
Powell, Michael, "Boston's
Big Dig Awash in Troubles", Washington
Post, 2004-11-19, Retrieved on Aug