The Marsupial Bridge is a pedestrian walkway that uses the existing Holton Street Viaduct structure as its "host". The bridge weaves through the existing structure that was originally engineered to support trolley cars, a transportation system which was abandoned with increased automobile use in the early 1900s. Hanging opportunistically from the over-structured middle-third of the viaduct, The Marsupial Bridge responds to the changing transportation needs of the city by increasing pedestrian and bicycle connections. The bridge is a "green highway" that activates the unused space beneath the viaduct, encourages alternative forms of transportation, and connects residential neighborhoods to natural amenities, Milwaukee’s downtown, and the Brady Street commercial district. The Marsupial Bridge’s undulate concrete deck offers a counterpoint to the existing steel members of the viaduct, inspired by the notion of weaving a new spine through the structure. Recalling the wood docks along the Milwaukee River, formerly an industrial corridor linking northern territories with the Great Lakes, the concrete deck is finished with wood deck and handrails, and stainless steel stanchions and diaphanous apron. Floor lighting is integrated behind the apron, and precision theatrical fixtures are mounted above to create a localized ribbon of illumination with minimal spill into the riparian landscape below.