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McMahon was part of a Design-Build (D-B) team for the superstructure replacement of the Commonwealth Avenue Bridge, which is over Interstate 90 (I-90) and the MBTA commuter railroad in Boston. As a key member of the D-B team, McMahon was responsible for preparation of the temporary traffic control, traffic signal, and lighting plans for the August 2017 and August 2018 replacement of the bridge structure.

McMahon coordinated with the project team to design effective temporary traffic control plans that allowed the contractor to replace the bridge in the most cost and time-effective manner. Traffic control for this project involved the full closure of Commonwealth Avenue and shut-down of the Green Line for approximately two weeks and closures on I-90 for 10 days. McMahon  developed plans to manage pedestrians, bicycles and vehicles, including MBTA and other shuttle buses affected by the closures. Plans included complicated construction detours, including creation of separate lanes for buses only through the work area, crossovers on I-90, and an extensive real-time traffic management system. Final design included enhanced bicycle and pedestrian accommodations, supplemented with innovative solutions, such as floating bus islands.

McMahon participated in numerous meetings with MassDOT, MBTA, the cities of Boston and Cambridge, Boston University, emergency responders, and many other stakeholders to review designs and discuss potential construction traffic management alternatives. McMahon also oversaw MBTA and Boston University buses “test run” through the proposed contra-flow detour route to avoid transit service disruption. This test run enabled us to field verify the proposed set-up and ensure that bus operations would be comfortable with the unusual turns and narrower travel lanes.