Recognized as the largest, most complex, and technologically challenging highway project in the history of the United States, the Central Artery/Tunnel Project significantly reduced traffic congestion and improved mobility in one of America’s oldest and most congested major cities. In addition, it helped improve the environment, and established the groundwork for continued economic growth for Massachusetts and all of New England.
The Project replaced Boston’s deteriorating six-lane elevated Central Artery (I-93) with an 8-to-10 lane state-of-the-art underground highway, added two new bridges over the Charles River, extended I-90 to Boston’s Logan International Airport, and Route 1A, created more than 300 acres of open land and reconnected downtown Boston to the waterfront.
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, then governor Michael Dukakis and then Secretary of Transportation Fred Salvucci devised the strategy of tying the two projects together.
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. Congress overrode his veto and ground was first broken in 1991.
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.
The project received approval from state environmental agencies in 1991, but didn’t receive federal environmental clearances until 1994.
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, 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 tunnel also had to pass under South Station’s 7 tracks, which carried over 40,000 commuters and 400 trains per day. To avoid multiple relocations of train lines while the tunneling advanced, a specially designed jack was constructed to support the ground and tracks. Construction crews also used “ground freezing” 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 project was managed by the Massachusetts Turnpike Authority. Because of the enormous size of the project, 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.
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.
A LEGACY OF PROBLEMS
As far back as 2001, Turnpike Authority officials and private contractors knew of thousands of leaks in the 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 result of Modern Continental and other subcontractors failing to remove gravel and other debris before pouring concrete. These problems were not made public.
On September 15, 2004, a major leak in the Interstate 93 north tunnel forced the closure of the tunnel while repairs were conducted. It also forced the Turnpike Authority to release information regarding its non-disclosure of prior leaks. A follow-up report stated 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.
In June 2005, Massachusetts State Police searched the offices of Aggregate Industries, the largest concrete supplier for the underground portions of the project. They seized evidence that Aggregate delivered concrete that did not meet contract specifications. In May 2006, six employees of the company were arrested and charged with conspiracy to defraud the United States. Immediately after the arrests, Massachusetts Governor Mitt Romney announced he would return $3,900 in political contributions from employees of Aggregate Industries.
Fatal ceiling collapse:
A fatal accident raised critical 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 and measuring 20’ by 40’ 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 complete safety audit, which was conducted by the Illinois engineering firm of Wiss, Janney, Elstner Associates, Inc.
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 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.
Powers Fasteners, the makers of the adhesive, revised their product specifications in 2007 to increase the safety factor from 4 to 10 for all of their epoxy products intended for use in overhead applications. On December 24, 2007, the Del Valle family announced they had reached a settlement with Power 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.
In February 2011, a maintenance crew found a fixture lying in the middle travel lane on the northbound O’Neill 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. fixture was in fact one of the fixtures used to light the tunnel itself. Further investigation revealed that the fixture’s mounting apparatus has failed due to salt water corrosion. A comprehensive inspection of the other fixtures in the tunnel revealed the numerous other fixtures were also in the same state of deterioration. Moving forward with temporary repairs, members of MasDOT administration team decided not to release news of the systemic failure and repair of the fixtures to the public or Governor Deval Patrick’s administration.
Before 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 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 co-mingled 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 to 14,800 hours per day after the project was largely complete. Travel times on the Central Artery northbound during the afternoon peak hour were reduced 85.6%.
The Big Dig was the most expensive highway project in U.S. history and was plagued by escalating costs, scheduling overruns, leaks, and design flaws, charges of poor execution and use of substandard materials, criminal arrests, and four deaths. The project was scheduled to be completed in 1998 at an estimated cost of $2.8 billion. The project was not completed until December of 2007, at a cost of over $14.6 billion. The Boston Globe has estimated that the project will ultimately cost $22 billion, including interest, and that it will not be paid off until 2038.
As a result of the deaths, leaks, and other design flaws, the consortium that oversaw the project agreed to pay $407 million in restitution, and severalsmaller companies agreed to pay a combined sum of approximately $51 million.
Editor Phil Robertson is an award-wining journalist and graphic designer. With a degree from the University of Florida’s School of Journalism, his career in journalism and publishing spans over 30 years, and includes positions as editor and publisher for several newspapers and magazines. During his career he has received a first-place award for investigative journalism from the Society of Newspaper Editors, and five ADDY awards for advertising design.