To generate the desired sense of flow and movement where none existed before, the structure takes a sinuous and asymmetric form inspired by the new precinct’s design parti of “pebbles in a stream.” And although the form may appear to be willful, said Patrick McCafferty, associate principal at the local office of Arup, structural engineers for the project, in this case, “beauty lies at the confluence between formal restraint and formal driver.” The form is an organic resolution of the factors in play: specific site boundaries, geometric constraints imposed by the rail authorities, preferred views, and the desire for a dynamic quality to draw pedestrians across.

Weathering steel plates forming the eastern parapet are canted outward in plan, like gills, to provide glimpses of the new precinct and the city beyond. The western parapet, in places more than 16 feet high, incorporates a welded steel box beam that performs the bridge’s heavy lifting, and also integrates path lighting along the length of a fluid line in the steel. Both parapets are tilted outward from the vertical to open the space between them to the sky. At their ends, they dissolve into a cut latticework that will enhance the bridge’s openness, and make visible the movement of pedestrians as they come and go across this dramatic new element in Boston’s urban fabric.

Time-lapse video © Payette, video by Tanguy Marquis