St. Croix River Crossing: Where Habitat Shapes Form to Meet Function
Advocates of building a new bridge over the St. Croix River faced an uphill challenge that had persisted for decades. They argued that the old Stillwater Lift Bridge — crossing over a lower section of the river which forms the border between Minnesota and Wisconsin — was impeding economic growth and also causing traffic congestion in the town of Stillwater, Wisconsin. The goal was to provide a new crossing bridge that could handle more traffic and divert it away from the lift bridge, which must be left in place since it is on the National Historic Register. However, conservationists and some local community members opposed building a new bridge in part due to environmental concerns, since the St. Croix River is designated as a National Wild and Scenic River protected by the United States National Park Service.
As a result, any new bridge would not only need to address all environmental concerns, but also relieve traffic problems, provide safe passage for pedestrians and vehicles, and be aesthetically designed to blend in with the location’s beautiful natural setting.
HDR Senior Vice President Craig Lenning served as the project manager on our award-winning St. Croix Crossing extradosed bridge design project. In the environmental process, our client and stakeholders already had selected this extradosed design to address all concerns, such as minimally impacting the river banks and enhancing the bridge’s visual profile. Because the extradosed bridge uses a structure frequently described as a cross between a concrete box-girder versus a cable-stayed bridge, the unique design leveraged the most serviceable aspects of both girder and cable-stay bridge structures in order to achieve its goals.
Once fully completed, this river bridge linking Oak Park Heights, Minnesota, with St. Joseph, Wisconsin, will be the second extradosed bridge built in the U.S. and the longest in North America.
Lenning recently co-authored a project feature story providing a technical overview of the bridge’s complex and intricate design process. In his article for ASPIRE magazine, St. Croix River Crossing, he explores how the bridge’s unique design resulted in “a lighter, cleaner, and more aesthetically pleasing pier arrangement with a smaller footprint in the environmentally sensitive river."
This article was originally published in ASPIRE, The Concrete Bridge Magazine from the Precast/Prestressed Concrete Institute, in the Fall 2018 issue. Available here with permission.