Rehabilitating the complex and historic “Salt and Pepper” bridge included restoration of its four cracked and leaning granite towers, which resemble salt and pepper shakers. Work also included repairing cast iron guard rails and fabricating traditional rivets for connecting vertical steel columns.

The $306.5-million design-build project included upgrading structural and seismic capacity and functionality while complying with strict federal and state historic rehabilitation standards. The 112-year-old bridge was last rehabilitated 60 years ago and had significant deterioration. “The scope encompassed the complete reconstruction of the original 11 open-spandrel steel arch spans and a 12th span that was installed later; the seismic retrofit of 12 masonry substructures; and the reconstruction of the four granite towers flanking the main span,” the team says.

Traffic management was challenging since the bridge—a critical transportation link that carries 28,000 vehicles and the MBTA’s Red Line’s 90,000 passengers daily—was kept in service during construction. Creative phasing helped the team reduce the number of weekend closures on the Red Line to 22 from the original plan of 25. The three-year project was originally scheduled for completion by 2016, but it was extended to 2018 due to “a need to redesign the steam line under the bridge; steel fit-up challenges; fabrication issues; issues involving historical details; and application of the coating system,” the team says.

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