Connecting Communities: Arup and Boston’s Green Line Extension

By Luke Carothers

During the 1980s and 90s, Massachusetts and the federal government joined together on an unprecedented investment.  A major part of this investment was the elimination of an Urban-Renewal era elevated highway–known locally as “Big Dig”–that ran directly through the center of Boston for decades.  Along with the removal of the elevated highway, this investment was coupled with the construction and restoration of numerous transit and heavy rail projects as well as the opening of numerous new urban parks.  The last of these planned transit projects was the extension of the Massachusetts Bay Transportation Authority (MBTA) Green Line.  This expansion extends the light-rail line from its existing terminus in East Cambridge, immediately outside the boundary of municipal Boston, into the adjacent municipalities of Somerville and Medford. The GLX totals 4.7 miles of new light rail tracks, six new stations, a new vehicle maintenance facility, the reconstruction and relocation of Lechmere Station, three new traction power substations, and a community path extension for cyclists and pedestrians that follows much of the GLX route. 

In the past, the residents in these areas relied heavily on streetcars to connect to employment opportunities, education, healthcare, and recreation.  Over the years, these streetcar lines were eliminated or replaced by bus routes.  Despite the short distance to Boston, Somerville and Medford lacked easy access by transit into the core of the city, and residents had to rely on arduous, multi-seat bus and rail trips to reach destinations previously serviced by streetcars.  The Green Line Extension project (GLX) was conceived as a way to meet the clear demand for a higher level of transit service.  The GLX project also attempts to rectify environmental and public health harm that had been done to East Cambridge and East Somerville during the period of urban highway construction.  The GLX is forecasted to add 50,000 daily passenger trips to Boston’s transit network, which will put the city one step closer to meeting its goal of carbon neutrality by 2050, significantly reducing personal vehicle trips and associated air emissions.

The GLX project broke ground in 2012, and, only three years in, the MBTA disclosed that the project’s costs had increased significantly, thus jeopardizing its completion.  Over the project’s first three years, the original project team worked hard to meet the needs of a broad base of public and community stakeholders, who had high hopes for the long-awaited transit line.  These efforts led to an inflated project scope and a steep increase in costs.  When Arup came on board in 2015, their task was to work with the MBTA and stakeholders to determine if the project could be scaled back to something more efficient and affordable, while still performing at expected levels.

With these goals in mind, the MBTA brought Arup onto the project in October 2015 to assist in performing a full scale evaluation and re-redefinition of all aspects of the GLX project–from scope and schedule to programming and procurement.  As a multidisciplinary firm, Arup gave the project a new set of eyes.  The first step in this process was working with the MBTA to initiate scope reductions as well as a design-build process that enabled officials to cut costs by $700 million while still meeting the requirements of the Federal Transit Administration full funding agreement for the project.  Among the schedule and money-saving recommendations outlined by Arup were: downsizing stations to eliminate redundancies and unnecessary flourishes, rehabilitation of some of the bridges inside the project’s footprint instead of replacing them, and delivering the project through a design-build contract instead of a construction manager/general contractor delivery model.  

Arup reviewed all aspects of the design and found opportunities to reduce cost and complexity while improving construction methods and design decisions.  This required Arup working collaboratively with the MBTA and project stakeholders to deliver a slimmed-down design that convinced both state and federal leadership that the project should continue.  By being patient and being attuned to project challenges, Arup’s staff have overcome challenges and delivered the vision and strategic guidance needed on a very tight timeline.  As a result of this work, the Green Line Extension project came back to life.

This work has a direct impact on communities that have been affected by transit inequity.  The GLX project will bring 80 percent of the community within walking distance of rail transit, compared to 20 percent previously.  This long-anticipated transformation will finally connect the Somerville and Medford communities–both of which are densely populated and historically underserved–to much-needed transit, and the community path furthers Boston’s ongoing investment in accessible and safe biking infrastructure as a viable transportation alternative.  As the GLX project progresses, ridership is growing and there are new opportunities for residents of all ages.

Luke Carothers is the Editor for Civil + Structural Engineer Media. If you want us to cover your project or want to feature your own article, he can be reached at lcarothers@zweiggroup.com.