Many large cities have natural and man-made elements that create obstacles to intensification and growth. These elements include bodies of water, such as rivers and lakes, and transportation features such as roads, railways and canals. With easily developable sites becoming increasingly scarce, cities such as New York and Toronto are responding to these obstacles, particularly by building next to or over rail and transit, by developing bridging elements that span over rail lines and roadways. This approach connects communities and reclaims previously unusable space by creating pedestrian plazas and urban parks, as well as supporting new developments that can include commercial, residential and mixed-use buildings.
As part of the Manhattan West project in New York City, a segmented precast multiple bridge structure was constructed to span over 16 rail lines of the busiest commuter rail corridor in North America. The Western Rail Yard, part of the Hudson Yards development in Manhattan, will feature high-rise towers built on top of a platform spanning the existing rail corridor. In Toronto, buildings are being designed to be built over subway lines to intensify the area and optimize the use of its transit facilities, such as at the proposed Canada Square development. Other projects include a design of a 8.5-hectare park over an active rail corridor, and the creation of bus stations and park areas around large and busy roadways. Building over and around rail and other transit facilities can create issues with fire and life safety, security and carries special logistical considerations. This presentation covers structural design considerations and related mechanical, electrical and architectural design decisions.