HDR St. Croix Bridge Crossing Project Wins Big in Minnesota, Advances to National Engineering Competition

HDR’s St. Croix Crossing project for the Minnesota Department of Transportation and Wisconsin Department of Transportation was recently honored with three awards by the American Council of Engineering Companies of Minnesota and will advance to the national competition held in April. It was named the People’s Choice Award winner in addition to receiving both a Grand Award and the Grand Conceptor Award, the state’s top honor.

The largest public works bridge project in Minnesota’s history, the St. Croix Crossing provides faster access to jobs in the Twin Cities and is also expected to support development in western Wisconsin. Five decades in the works, it balances environmental concerns while providing increased vehicular capacity between Minnesota and Wisconsin. The longest extradosed bridge in the country, it crosses the federally protected St. Croix River. (An extradosed bridge employs a structure which combines the main elements of both a prestressed box girder bridge and a cable-stayed bridge.)

HDR and COWI provided consulting services for this project. The team’s concept optimization process decreased the structural complexities of the bridge, including the complex geometry of the approach structures and the elimination of two towers from the main span.

With the intent and guidelines laid out in the environmental impact statement, designers minimized the new crossing’s impacts on the river — optimizing the design to remove two towers from the water and designing piers to resemble reeds and cattails. Tucked into the river valley, the earth-toned bridge offers a blueprint to other Departments of Transportation on how to integrate infrastructure into the natural setting.

Throughout design and construction, extra care was taken to protect nature by preventing disturbances to bald eagle nests, relocating mussels and endangered flowers, and preserving historic structures. To minimize impacts to the Wisconsin bluff, designers aligned the new bridge with an existing ravine — reducing the need to cut into the highly erodible bluff line and creating a smooth transition from highway to bridge.

The St. Croix Crossing also provides major improvements for commuters, mitigating the delays and accommodating 55,000 more vehicles per day than the lift bridge. The lift bridge will not disappear, though. After renovation, the National Register of Historic Places-listed bridge will be converted into a pedestrian crossing and integrated into a new 5-mile trail system.

Given complications and challenges stemming from the federally protected river, the project required both congressional approval and a presidential signature. Further, to eliminate questions of what would be built, a stakeholder process determined the extradosed structure, along with 6 miles of roadway improvements, lift bridge refurbishment and other mitigation items.

About HDR

For more than a century, HDR has partnered with clients to shape communities and push the boundaries of what’s possible. Our expertise spans nearly 10,000 employees, in more than 225 locations around the world — and counting. Our engineering, architecture, environmental and construction services bring an impressive breadth of knowledge to every project. Our optimistic approach to finding innovative solutions defined our past and drives our future.