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 41 (US 41) and M-26are both routed across the bridge.
The original bridge on the same site was a wooden swing bridge built in 1875. The bridge was built by James P. Edward of Fox and Howard Inc. of Chicago. Three local men raised $47,000 in stocks for the toll bridge. Construction began in the spring of 1875 and was finished in the spring of 1876. This was replaced by a steel swing bridge, the Portage Canal Swing Bridge, built by the King Bridge Company in 1901. The Portage Canal Swing Bridge was damaged when a ship, the Northern Wave, collided with it in 1905. The center swinging section of the bridge was replaced and a similar incident almost occurred again in 1920, but the ship was able to stop by dropping its anchor, which snagged on the bottom of the lake. In 1959, the Portage Canal Swing Bridge was replaced, at a cost of about 11-13 million US dollars (sources vary), by the current bridge which was built by the American Bridge Company.
As its name states, this moveable bridge is alift bridge with the middle section capable of being lifted from its low point of four feet clearance over the water to a clearance of 100 feet (30 m) to allow boats to pass underneath. 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 bridge is a crucial lifeline, since it is the only land based link between the north (so-called Copper Island) and south sections of the Keweenaw peninsula.
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.
Hancock and Houghton hold an annual celebration called Bridgefest to commemorate the opening of the bridge which united their two communities.