The Portage Lake Lift Bridge (officially the Houghton–Hancock Bridge) connects the cities of Hancock and Houghton, in the US state of Michigan, across Portage Lake, a portion of the waterway which cuts across the Keweenaw Peninsula with a canal linking the final several miles to Lake Superior to the northwest. US Highway 41and M-26 are both routed across the bridge.
The bridge is the world’s heaviest and widest double-decked vertical-lift bridge.More than 35,000 tons of concrete and 7,000 tons of steel went into the bridge, which replaced the narrow 54-year old swing bridge, declared a menace to navigation on the busy Keweenaw Waterway.Its center span “lifts” to provide 100 feet (30 m) of clearance for ships.
The original 1959 design by Hazelet and Erdal of Chicago of the bridge’s liftspan had roadways constructed on both levels with rails imbedded in the road surface on the lower deck. This allowed the span to be partially raised to allow small and medium boat traffic to pass underneath without disrupting vehicular traffic. From this middle position, the span would then only need to be raised for large ships or lowered to allow trains to cross. With the end of rail service in 1982, the lowest position is no longer needed to allow trains to pass so the bridge is not lowered below the middle position during the summer boating season except for periods of maintenance or repair. In the winter after the lake freezes, the bridge is placed in the lowest position to allow the lower deck to be used by snowmobile traffic