Maffa Way and Mystic Avenue Bridge Replacement

Located in Sullivan Square, one of Boston’s most constrained and heavily traveled transportation hubs, the Maffa Way and Mystic Avenue bridges span seven active rail lines beneath the eight-lane I-93 Viaduct. Together, they form a critical corridor for commuters, freight, pedestrians, cyclists, and transit users. MassDOT required a resilient, low-maintenance solution that could modernize the crossings while maintaining continuous rail and roadway operations in an exceptionally complex setting.

In a design-build partnership with Skanska, CHA delivered an innovative replacement strategy focused on constructability, resilience, and long-term value. Severe geometric constraints left little room to raise roadways, prompting the design of custom ultra-shallow steel plate girders to achieve required railroad clearances while allowing reuse of existing substructures. Additional innovations—ultra-light foamed glass aggregate, seismic isolation bearings, inverted seismic shear keys, and simplified half-section pipe stiffeners—enhanced performance, simplified fabrication, and avoided extended rail shutdowns. Durable weathering steel and concrete-encased beam ends further minimized long-term maintenance over the bridges’ 75-year design life.

With only two nine-day Orange Line shutdowns and eight weekend commuter rail closures available, the team relied on accelerated bridge construction techniques to complete major work within limited surge windows. Finished on schedule and within budget, the renewed bridges strengthen multimodal connectivity through dedicated bike lanes, widened ADA-compliant sidewalks, and improve transit operations, supporting MassDOT’s Complete Streets and Vision Zero goals while setting a benchmark for urban infrastructure modernization.