Green Line Extension Viaduct

The Green Line Extension added 4.7 miles of light rail and seven stations north from Lechmere, much of it on new steel-girder viaducts that thread over the active commuter-rail corridor and, at Union Square, between the columns of the main viaduct with inches to spare. Atlantic Bridge & Engineering was the viaduct steel erector, first engaged for the White-Skanska-Kiewit viaduct package in 2015 before the program was reset, and then for the design-build joint venture GLX Constructors (Fluor, Middlesex, Herzog and Balfour Beatty) from summer 2019 to spring 2020.

ABE crews set the plate girders and diaphragms, simple, continuous and curved spans and the railroad through-girders, across the Medford Branch, both Union Square branch viaducts, the yard lead flyover and the Lechmere-end spans, plus the Washington Street and Broadway bridges. Each span went up with its bearing and sole-plate assemblies field-welded, stay-in-place deck installed and about 68,000 shear studs furnished and installed, sequenced around the MBTA's live Fitchburg and Lowell lines.

Under a separate contract with Consigli, ABE also furnished and erected the station steel: platforms, canopy frames, head houses, stairs, railings and elevator steel at Union Square, East Somerville, Magoun Square and Ball Square, and the Pearl Street and Ball Square traction power substations. The Union Square branch opened in March 2022 and the Medford branch that December.