Bridges, Tunnels and other Transportation Structures
The intent of this presentation is to depict how the modern societal transportation needs and several other constraints influenced the design of the $177 million North Washington Street Bridge (Charlestown Bridge) over the Boston Harbor that will replace the existing bridge. Constructed in 1898, the existing twelve span bridge carried two trolley car racks, two elevated street railway tracks, six lanes and two sidewalks from Keany Square in Boston to City Square in Charlestown. Several utilities, including two 6” diameter 115kV HPFF transmission lines which cannot be relocated during construction and must be supported every ten feet, are carried by the bridge. In a poor state of repair and stripped of some of the original features of the bridge, such as the operable swing spans and elevated railway tracks, the existing bridge sees an ADT of 42,000 vehicles. The bridge is on a hazardous cargo route and is also the evacuation route for the city of Boston. Its east sidewalk carries Boston’s Historic Freedom Trail.
To incorporate the aforementioned requirements into a livable, walkable, sustainable and multimodal bridge, the context sensitive final design delivers a visually appealing bridge that replicates a complete city street in a historic bridge location at an important waterfront. Embellished with architectural trellises, landmark plaques, interpretive panels and accent lighting, the proposed signature bridge would carry four lanes of vehicular traffic, one designated BRT lane, two separated bicycle lanes, curbside plantings along the entire length of the bridge, and wide sidewalks with observational build-outs on cantilevered floorbeams integral with the four steel box girders supported on five V-piers.