Urban Bridges

Boston, Massachusetts

The Urban Bridges project was awarded first place in the 2003 international Design for Density design competition sponsored by the American Institute of Architects. Located on a non-existent site – the airspace over the Massachusetts Turnpike in Boston – the project spans the 200' wide highway cut with a dense typology of sustainable, functionally mixed bridge buildings. Conceived as multi-story Vierendeel trusses, the buildings are modeled on the traditional block scale and rowhouse typology of adjacent neighborhoods. A regular rhythm of intimately scaled pedestrian streets interspersed between new vehicular streets form a rich and varied public realm in which publicness may unfold. Balancing the deck cost and building height relationship with the desire for continuity in the urban fabric and acknowledgment of the historical cut, a sectional strategy simultaneously mends the ground and selectively reveals the multi-layered site history to those at all levels and speeds of movement. One peer reviewer commented, “This submission describes an intriguing proposal for the use of space above transportation arteries. The historical, theoretical and implementation aspects of the project are clearly articulated and the end result provides a good example of a well-rounded research investigation.”

Two city blocks flanking Washington Street are subdivided into six mixed-use blocks by one new local street at grade and four pedestrian streets above two internal parking levels. These new streets and courts, edged by retail and small-scale commercial uses with residential above, will create active public spaces integral to the city structure. Rejecting the equation “green space = public space,” the streets themselves are the public space of the city. Buildings are aligned along the North-South axis so that all dwellings receive daily direct sunlight. Green roofs provide a recreational “backyard” for residents, and photovoltaic panels on the upper roofs take advantage of solar income.

The narrow, serial block structure perpendicular to the turnpike cut is inextricably linked to the housing typology itself. Each block is a structural truss spanning the 200’ gap, thereby avoiding the construction of a uniformly heavy concrete deck. Given the direct relationship between deck cost and building height, quality of life considerations, and the intimate scale of surrounding neighborhoods, we designed mixed use, low and mid-rise buildings that balance density and livability.

Unlike most highrise buildings, the buildings will give residents greater contact with the “ground,” contain diverse uses and live/work opportunities, reduce the number of units that share vertical circulation, and provide each dwelling with light and ventilation from at least two sides. Ranging from 20’ to 50’ in width and 6 to 12 stories in height, the buildings provide unit types of varying area, configuration and cost. The lower two floors contain retail, office and community uses with two levels of concealed mid-block parking. This programmatic and spatial layering will establish a vibrant density of people living, working and playing, while balancing communal and private life.

The structural idea for this scheme was driven by a desire to find a solution specfic to construction of rowhouses and more effective than the usual decking method of an anonymous thick concrete platform. The project spans above Boston’s Massachusetts Turnpike with a dense typology of sustainable, functionally mixed, mid-rise blocks. Our urban approach respects the existing layers, context and unseen history embedded in the site, and attempts to make history visible. A formal and spatial design strategy that integrally conceives of the public realm, urban structure and architectural typology results in a series of thin bridge buildings modeled on the traditional block scale and rowhouse typology of adjacent neighborhoods. The bridges link these neighborhoods, while emphasizing and recalling movement through the Neck on Washington Street.