Massachusetts used accelerated bridge construction to replace more than a dozen aging structures on a major interstate -- 5 years of work in just 10 weekends.

Interstate 93 in Boston functions as the city's transportation backbone, connecting the many paved appendages that carry the residential, commercial, and tourism traffic in the region. Built in the 1950s and 1960s, the corridor received a major facelift a decade ago as part of the Central Artery/Tunnel Project, also known as the Big Dig.

Motorists heading north on I-93 pass over the project's Leonard P. Zakim Bunker Hill Bridge, as the interstate begins its march out of the Boston area. With four lanes northbound and four lanes southbound, the highway carries 200,000 vehicles per day and, aside from routine resurfacing and safety upgrades, stands much as it did 50 years ago.

In 2009, an interstate maintenance project set out to resurface a segment of the I-93 corridor in Medford, MA, about 2 miles (3.2 kilometers) from Boston's city limits. The bridges' project scope was limited to replacing the wearing surfaces at the seven overpasses within the corridor. The existing asphalt surfaces wore a history of scars from rapid-set concrete deck repairs. Over the years, crews had performed these repairs on an as-needed basis at night but were chased out in the early morning by commuters reclaiming the road for themselves. Despite these efforts, the pounding of a half-century's traffic, coupled with annual doses of deicing salts, had caught up with the concrete and steel superstructures. The bridges needed more than resurfacing. They needed replacement.

The Massachusetts Department of Transportation (MassDOT) was aware of the deterioration and had begun exploring options to replace the bridges. The major challenge was determining how to manage traffic during construction. With no right-of-way available to reroute vehicles, MassDOT estimated that a conventionally staged replacement could take 5 years with five separate traffic configurations. This approach also would have required sections of the existing bridges to provide 4 more years of service.

Meanwhile, efforts to resurface the bridges under the interstate maintenance project met stiff resistance. Once crews removed the asphalt from the bridges, they found the decks were in poor condition and extensive repair was necessary. The frequency and magnitude of repairs quickly reached a crescendo. On August 3, 2010, and again the following day, localized failures occurred on the Valley Street bridge deck during rush-hour traffic. The lane closures required to do repairs, and the resulting traffic congestion, convinced MassDOT officials of the need for a permanent fix. In the shadow of the impaired bridge, as crews worked to reopen the closed lanes, then MassDOT Highway Division Administrator Luisa Paiewonsky informed the media that MassDOT planned to replace all 14 bridges within the Medford corridor -- 7 northbound and 7 southbound -- in summer 2011.

Following the announcement, work began on the I-93 Rapid Bridge Replacement Project, known as the I-93 Fast 14.

Preliminary Design

MassDOT developed a replacement concept for the Medford bridges under the Commonwealth's Accelerated Bridge Program, which Governor Deval Patrick had launched in August 2008 to reduce the number of structurally deficient bridges in Massachusetts. The program employs innovative design, project management, and construction techniques, including alternative procurement methods, aggressive traffic management, and prefabricated bridge components. These elements formed the foundation for I-93 Fast 14.

Most of the existing bridges consisted of three-span, steel girder superstructures with cast-in-place decks, all with substructures of concrete abutments and piers. As manifested during the many repairs over the years, the existing decks were chloride saturated, and the structural steel suffered from section loss (a reduction of steel cross section caused by corrosion) at the beam ends due to leaking expansion joints. The substructures, however, aside from normal deterioration, were in salvageable condition. Therefore, MassDOT opted to repair and reuse the existing substructure but replace the superstructure with prefabricated modular units.

With four lanes in each direction and traffic demand requiring use of every lane, long-term closures were out of the question. Borrowing a traffic management approach used by the Virginia Department of Transportation and others, MassDOT proposed constructing temporary crossovers at either end of the project corridor, and deploying a movable barrier to divide one side of the highway for bidirectional, two-lane operations. Bridge work then could proceed on the closed side of the highway. With short work windows on weeknights, MassDOT confined crossover use to the weekends. The agency and its contractor had a 55-hour window from 10 p.m. Friday through 5 a.m. Monday to complete the bridge replacements and fully reopen the interstate for traffic before the morning rush.

Planners, construction personnel, and bridge and traffic engineers developed the project concept and refined the details in a collaborative environment via regular project team meetings. The preliminary design included collaborative multiagency involvement from members of MassDOT, the Federal Highway Administration's (FHWA) Massachusetts Division, the city of Medford, and public safety and transit agencies. With no single group designing in a vacuum, the multidisciplinary atmosphere helped ensure the success of the final design, which varied little from the original concepts.

"With an aggressive schedule like this, you don't have the time to wait for each engineering discipline to provide separate reviews, comment on the design conflicts, and find resolution," says MassDOT District 4 Highway Director Patricia Leavenworth. "You have to work as a team, anticipate the design decisions that will cross multiple disciplines, and work collaboratively on the solutions before the design details are even drawn."

Aggressive Schedule

According to the schedule Paiewonsky set forth, preliminary design, contract procurement, and preparatory construction activities were all to take place between late August 2010 and spring 2011, with actual bridge replacement in the summer. With traffic volumes beginning to lessen for summer in June, and Independence and Labor Days off limits for construction, a look at the calendar offered 12 weekends during which the actual bridge replacement could take place. Allowing 2 weekends for contingencies, MassDOT arrived at a schedule of 10 weekends.

"Fourteen bridges in 10 weekends -- it sounds like a bungee jumper's memoir, but it was an ambitious goal for bridge replacement, to say the least," says MassDOT Highway District 4 Project Development Engineer Frank Suszynski. "Meeting the schedule with conventional procurement methods would have been impossible, so we chose to use design-build contracting."

Design-build contracting helped accelerate project delivery by combining the design and construction phases into a single contract. In addition, MassDOT incorporated an incentive/disincentive clause, which was contingent upon completion of all the bridges by summer's end and timely reopening to traffic each weekend. If the schedule was fully realized, the contractor could earn a $6.9 million incentive, a significant amount when compared to the winning bid of approximately $78 million.

Mindful of the short window, MassDOT expended considerable efforts to prepare for the design-build team. Extensive research on utilities in the corridor identified assets likely to affect or be affected by the project. Where required, utility coordination and relocation work was performed independently of the construction contract. MassDOT also coordinated its other projects to lessen the adverse effects on regional traffic during the weekend work. Toward this end, MassDOT modified work hours on the other projects and shifted schedules as necessary. In addition, the I-93 Fast 14 projects' scope overlapped with some ongoing projects in the corridor, so MassDOT folded that work into the new contract as well.

"We really didn't have the time to design a project that would fit well into our overall construction program and our available resources," says Leavenworth. "We had to make our construction program and resources fit the project. It's kind of like when your relatives visit from out of town and your parents made you give up your bedroom instead of making your relatives find a hotel."

Public Outreach

MassDOT began a comprehensive communications effort on the I-93 Fast 14 project while the design was still in preliminary stages. MassDOT held meetings with stakeholders to identify important values and guide local traffic planning and communications activities. Stakeholders included a broad array of emergency responders, elected officials, transportation and planning organizations, representatives of local commerce and the travel and tourism industry, other transportation providers, and community groups. The purpose of the communications effort was to provide all individuals with the information they needed to make the best possible travel and business decisions. Most important, project stakeholders worked diligently to distribute project information to their networks.

Specific efforts before and during construction included an interactive project Web site at ---, 511 messages, email alerts, highway advisory radio, portable changeable message signs showing real-time traffic information, as well as social and major media. Medford Mayor Michael McGlynn says that between "the tweets, the online [presence], the media, the access, they've done a great job of getting the message out there."

Contract Award

On September 20, 2010, just over a month after the deck failure, MassDOT held the first public information session for bidders. Oral presentations for the two shortlisted teams occurred on January 11, 2011, and bids were opened just 8 days later. MassDOT issued the Notice to Proceed on February 8, 2011, to a joint venture of J.F. White Contracting Co. of Massachusetts, and Kiewit Infrastructure Co. of Delaware.

"With a contract signed, the reality of the project set in quickly," says Ernie Monroe Jr., MassDOT area engineer for the Fast 14 project. "In just 4 months, we would attempt the construction sequence -- made to look so easy by computer-generated simulations -- with real personnel, materials, and equipment. The traffic management plan would no longer be lines on a page, and thousands of motorists would now test the wisdom of the scheme."

As during the preliminary design phase, the agency held weekly meetings at a shared MassDOT/contractor field office. Meetings were attended by a multidisciplinary group of professionals from MassDOT, the design-build team, and FHWA's Massachusetts Division to provide timely input and design review. The meetings began with an "all hands" update on the project status and then broke into discipline-specific submeetings. The innovative techniques included in the project challenged agency standards and practices, which required MassDOT decisionmakers to be present at the meetings.

MassDOT committed to expedited reviews, and discussed and resolved comments at the weekly meetings. Each week, the design-build team distributed reports from its document tracking software, which clearly identified the status and criticality of each submission. In this process, MassDOT's review efforts were focused efficiently to enable the schedule to proceed as planned. In addition, use of a Microsoft^® SharePoint^® project site, a Web-accessible file repository, was critical for universal access to current design documents. Project team members also configured their SharePoint settings to receive email notifications of postings based on their discipline areas.

The meetings facilitated a key step in the design phase, the establishment of a required design submission for each bridge. Production of the prefabricated bridge elements required significant lead time, with orders to the manufacturer contingent upon significantly progressed plans.

Bridge Design

The basic design of the prefabricated bridge elements consisted of a reinforced concrete deck cast upon two steel girders. Typically, the cross section of each bridge was broken up into six units per span. In this manner, a typical three-span bridge required 18 units for construction. Each unit was cast with threaded inserts to accept reinforcement from the closure pours, which join the units into a unified bridge deck. In total, the project used 252 prefabricated units, all constructed in New Jersey and transported by truck to Massachusetts.

A key design feature was the integration of link slab detailing of the superstructure over the piers. This system eliminated potentially leaky expansion joints within the bridge deck, designing out a weak point that had contributed to the demise of the original structures. In broad terms, the design omitted shear connectors, making the deck non-composite by debonding the deck from the girders and adding additional deck reinforcement within a calculated distance beyond the pier centerlines. Depending on calculated expansion, the contractor installed extruded steel strip seals at the abutments. Of the 14 bridges, 6 structures required strip seals, whereas the other 8 simply have saw and seal relief joints cut into the final paving. Reducing or eliminating joints, which decreases the potential for chloride and moisture intrusion into the superstructure, improves the long-term durability of structures.

The critical component of the entire system was the concrete used in the closure pours. Given the 55-hour window for the weekend work, standard curing practices were not an option. To overcome this obstacle, MassDOT used a rapid-strength-gain concrete for the first time in the agency's experience. A considerable amount of research and testing went into the mix design. The contract required that the material achieve a compressive strength of 2,000 pounds per square inch (13,800 kilopascals) within 4 hours of final set, and imposed strict restrictions on the propagation of shrinkage cracking. The contractor met both parameters with a high-tech, admixture-enriched recipe.

Traffic Management

As the bridge engineers worked, MassDOT adapted the traffic management plan to the realities of construction in an urban environment. With the closure of the local roads below the bridges each weekend, specific detour plans were put in place to provide safe traffic circulation for the city of Medford. The major component of the traffic management plan, the crossover system, sought to fully close a portion of the interstate for the weekend. The traffic engineers realized, however, that access to the exit ramps before and entrance ramps after was sometimes possible, depending on the location of the bridge within the corridor. These subtleties contributed to the need for a separate traffic management plan for each of the 10 weekends. Each plan included a signed, primary detour route along a parallel arterial where motorists could access local destinations despite ramp closures.

As part of the contract, the design-build team set up a real-time traffic monitoring system. This system, using data on vehicle speeds gathered at strategically located traffic stations, provided engineers with the ability to observe traffic conditions for the whole corridor from a centralized location. The design-build team also converted the data into estimates of average trip times in the corridor, which in turn were displayed on portable, changeable message signs located at key decision points within the regional road network. Armed with the knowledge of current traffic conditions, motorists could choose to circumvent the corridor or continue through it.

"This Fast 14 project," says Federal Highway Administrator Victor Mendez, "is a great example of how you can literally take years off the time it takes to replace 14 bridges and do it while tens of thousands of motorists go about their daily routines."

Construction Preparation

Before construction could begin, a considerable amount of work needed to be completed. MassDOT and its contractor had to construct the crossovers, which required demolishing the existing median, relocating highway lighting, modifying the drainage system, and paving full-depth hot-mix asphalt for the crossovers. MassDOT also required the contractor to perform a test deployment of the crossover system in advance of actual bridge replacement. Likewise, the contractor performed a mock bridge assembly at a staging site to help personnel become acquainted with the process, techniques, and timing.

An even larger task was preparing each of the existing substructures to accept the new superstructures. In most cases, the revised structural framing added two extra beams to the existing spacing of the girders, which served to reduce the weight and dimensions of each unit and offset the proposed bearing locations from the existing ones. Relocating the bearings simplified advanced construction of the beam seats by allowing some of the existing bearings to remain in place. In total, workers formed and placed 1,008 reinforced concrete beam seats during the spring and early summer. Although the offset centerline of bearing made the job easier, 684 locations still required jacking, shoring, and coping of the existing beams to provide access to the new bearing location.

Weekend Work

The first weekend closure kicked off on Friday, June 3, 2011. Traffic management operations began at 8 p.m., with two barrier transfer machines marching through the corridor deploying the barrier in tandem. By 10 p.m., demolition forces had taken to the closed side of the highway, pulverizing and shearing their way through the first bridge.

By 9 a.m. the following morning, the majority of the former bridge had been carted offsite, and the massive hydraulic cranes required for the lifts took their positions and began assembly. Crews erected bridge components through late afternoon, followed closely by teams of carpenters forming the closure pours, and iron workers placing the reinforcing steel. By late afternoon, all three activities were occurring simultaneously.

Placement of the closure concrete began in the early morning hours on Sunday. Trucks delivered the ready-mix material to the bridge site in a carefully dispatched convoy, with the concrete having been tested for slump, air content, and temperature prior to release. The trucks backed onto the decks, straddling the closure cavities, and methodically discharged the material with finishers following close behind. Crews applied curing compound to the finished concrete and covered each closure section in plastic sheeting. Quality control inspectors tested samples taken from the trucks at a mobile lab, and once the samples achieved the desired compressive strength, the contractor could begin cleanup and prepare the bridge and approaches for Monday morning traffic.

Through careful planning and execution, the first weekend's activities were successfully completed and replayed nine more times throughout the summer. Some weekends even featured two locations under construction to complete the 14 bridges in 10 weekends. Through skilled management and personnel, the design-build team made the challenging project look routine.

Conclusion

By Labor Day 2011, motorists passing through Medford on I-93 did so with the support of new mainline structures. The Fast 14 project had accomplished its goal, 14 bridges in 10 weekends without any major incidents. Cast-in-place bridge barrier work, membrane waterproofing, and final paving proceeded through the fall, leading to substantial completion of all the bridges by November. The final project component, installation of a sound barrier on a portion of the corridor, is scheduled to be completed by July 2012.

"The contract was executed without delays or costly overruns," says MassDOT's Leavenworth. "And, more important, the Medford bridges were replaced without sacrificing safety or quality of life for the residents and motorists of the region. We will judge the project, once completed, by its competitiveness with conventional approaches, to better quantify its overall value. However, we are pleased with the end result."

MassDOT's initial findings suggest that the costs for this accelerated construction project are similar to those that would have been expected for use of conventional construction methods. However, future comparisons will include considerations for the reduced timeframe and user costs to the public.

As U.S. Secretary of Transportation Ray LaHood wrote in his "Fast Lane" blog, "This bold approach to replacing 14 different bridges on I-93 in Medford, MA, in a single summer demonstrates perfectly the ability of American innovation to respond to transportation challenges." He continues, "[The I-93 Fast 14 project] proves that America is ready, willing, and able to dream big and build big."

Jack Moran, P.E., is a project engineer with MassDOT's Highway Division. Moran leads in-house design for District 4, and he participated in procurement, design, and construction of the Fast 14 project. He holds a B.S. in civil engineering from the University of Massachusetts Lowell.

For more information, contact Jack Moran at 781-844-1774 or john.m.moran@state.ma.us.