Proj Overview
Precast Bridge Units accelerate viaduct repair

Route 1 is a vital gateway between Boston and northern communities. The highway carries over 65,000 cars per day as well as trucks and buses. The elevated section, known as the Chelsea Viaduct, was in need of repair. The project was strategically bundled with the Tobin Bridge project to minimize the impact on commuters and the residents of Chelsea.

The Massachusetts Department of Transportation (MassDOT) recognized that both structures were over 60 years old and essential to regional mobility. Beginning in 2017, during the planning stages, MassDOT conducted public hearings and outreach to affected communities.

The Chelsea Viaduct Rehabilitation project included substructure rehab, pier retrofits, bearing and structural steel replacements, deck replacement, and barrier upgrades. The project limits extended from the Maurice J. Tobin Memorial Bridge on the south to Orange Street on the north, covering the entire deck area for two viaducts and the ramps within those limits. 


Approximately 70% of the deck was replaced utilizing Prefabricated Bridge Units (PBUs). A PBU is essentially a mini bridge, consisting of two beams with a composite deck which are cast off-site prior to construction.

For the Chelsea Viaduct precast concrete decks were cast composite with the structural steel.  There was (313) PBU's covering approximately 138,000 SF of precast surface area.  There was also (198) precast grid panels covering approximately 27,000 SF.  PBU's were joined together with cast-in-place closure pours on site.  The deck also received an asphalt overlay and cast-in-place concrete barrier.  

The Skanska-McCourt Joint Venture (Skanska US and McCourt Construction Co.) started its work on the rehabilitation of the $169 million project in April 2019. Installation of the precast began in September of that same year and was completed in late 2020. 

While the PBUs were utilized throughout the majority of the viaduct work, conventional repair methods were also in the project scope.  New crash-tested bridge barriers and a solid snow fence were installed; roadway lighting was replaced and bridge drainage upgraded. The existing parking lots under the viaduct were rebuilt and all approach roads were reconstructed.


One of the goals of the rehabilitation of the Chelsea Viaduct was to improve the overall condition and safety of bridges under MassDOT's management. The viaduct has 75 spans. The southern viaduct is 2,000 ft. long and the northern viaduct 1,000 ft. long, each with several lanes in each direction. Maintaining Route 1 traffic during the project was a challenge. Accelerated bridge construction (ABC) techniques were utilized for reduced closure times during the staged construction.

Crews worked day and night, with crane operations occurring on a continuous basis, with just in time deliveries that required detailed coordination and planning. Some weekday and weekend lane closures were necessary to allow for continuous lifting operations.

Two types of beams were installed — PBUs, two beams placed together with concrete poured on them, manufactured by Fort Miller and diaphragm beams that support the PBUs. The beams range between 9 and 12 feet when all the concrete is poured, and they weigh between 25 and 50 tons. The PBUs were shipped in advance by trailers from the Fort Miller production facility and stored at staging area.

Bay Crane set the pieces overcoming challenges to situate the cranes in tight areas. When working in between the structures for middle sections, intermittent road closures were required for the safety of the traveling public and under the swing area of the crane.  Crews were able to work throughout the mild winter avoiding delays.

Heavy Picks

The PBU’s ranged from 20’ long up to 85’ long with the heaviest pick being approximately 150,000 pounds. There were cast-in-pace closure pours surrounding each of the PBU’s – at the longitudinal and transverse joints – tying the individual decks together. The fascia and median barrier were cast-in-place.

The completed deck received a membrane waterproofing and an asphalt overlay. The installation of the PBU’s was executed by Atlantic Bridge and Engineering with crane services provided by Bay Crane. Bay Crane also provided delivery service of the PBU’s. The majority of the precast installation was done during off-peak/night-time hours.

Fort Miller provided the precast components and Casco Bay from Maine provided the structural steel girders for the PBU’s and L.B. Foster Company provided the steel grid deck for the precast panels.

MassDOT rehabbed the structurally deficient viaduct while minimizing construction impacts through accelerated bridge construction techniques. The challenge was to minimize the duration and impact to the 63,000 vehicles per day using Route 1 and the MBTA bus routes that cross the viaduct and bridge, MassDOT re-sequenced the full deck and girder replacement and pier retrofitting for the viaduct and ramps to minimize total construction duration and limit their impact. This strategy lessened the duration of impacts to road users, improved the quality of life to those living around the structures, and minimized the risk of project delays. The end result is an upgraded structure with a 75 year design life and a reliable deck surface resulting in reduced maintenance costs and improved riding surface.


There are no records.
Project Team


The  Fort Miller Co., Inc., Schuylerville, NY


Massachusetts Department of Transportation, Boston, MA


HNTB, Boston, MA


Skanska - McCourt Joint Venture

Photo Credit:

Skanska - McCourt Joint Venture


Key Project Attributes

138,000 SF PBU's (Prefabricated Bridge Units)
27,000 SF Precast Grid Panels


Project/Precast Scope

313 PBU's (Prefabricated Bridge Units)
198 Precast Grid Panels