Portage Lake Bridge

The Portage Lake Bridge, completed in 1959, was an early application of bridge-slide construction in the U.S. and possibly the only double-decked lift bridge designed with an intermediate lift span position to minimize road closures due to water traffic.

The Portage Lake Bridge was completed in 1959 between the towns of Houghton and Hancock, Michigan, connecting that state’s mineral- and timber-rich Keweenaw Peninsula to the rest of the nation.  Its proximity to the older and adjacent swing bridge required an early application of floated-in, bridge-slide construction to prevent long and unacceptable delays to car, train, foot, and boat traffic to and from the peninsula, a major copper source during the early years of the bridge.

The Portage Lake Lift Bridge was unlike other lift bridges with its double deck, and possibly unique, with its intermediate lift position.  The lower deck served railroad traffic while the upper deck served automotive and pedestrian traffic.  The lower deck of the lift span was designed for all three transportation modes. Thus the bridge could be partially raised so the bottom deck of the lift span was even with the upper, fixed deck, allowing for passage of boats up to 35 feet tall without interrupting automobile and foot traffic.  This was the normal lift-span position. The span lowered for less frequent rail traffic, while allowing for automobile and foot traffic, and raised to its full height of 100 feet for larger marine vessels such as Great Lakes ore carriers.   Today, the lowered position is normal in winter when the lower deck is used by snowmobiles.     

Carl Winkler, Houghton County Road Commissioner, was first to recognize the severe limitations of the old swing bridge and spearheaded a 10-year effort to coordinate the Houghton County Road Commission, Michigan Department of Transportation, and state and nationally elected officials to gain approval and funding for its replacement.  With funding secured, Hazelet and Erdal Consulting Engineers of Chicago designed the innovative replacement bridge.  The prime contractors were Al Johnson Construction of Minneapolis and American Bridge Company.  The Michigan Department of Transportation managed the project and appointed three head engineers at various phases of the construction, Tom Gilroy, Thomas Wiseman, and John Michels, all Michigan Technical University graduates in civil engineering.   

The Portage Lake Bridge continues in use today carrying an annual daily traffic count of 25,000 vehicles.