According to the Truman Hobbs act of 1945, If a bridge is an obstruction to river traffic and a study shows that the benefits derived from replacement or repair of that obstruction are at least equal to the cost, then under the Truman Hobbs act of 1945, money can be appropriated for the work. Bridge 5.1 is just such an example of this process. During the Reagan administration, Congress authorized $38 million for reconstruction of bridge 5.1, as it proved to be an impediment to navigation into Portland and upstream Willamette.
The old bridge’s swing span, built in 1908 and pictured here, was the longest in the world. It was constructed as part of a triplet of bridges in 1908-09: bridge 8.8 over the Columbia Slough and 9.6 over the Columbia River, named as the miles from Portland’s Union Station. Bridge 5.1 was replaced in a two-year project concluding in 1989. A 516 foot long lift span, with a lift load of 8,000,000 pounds was successfully erected within the 72 hour time limit.
Interesting fact: The present lift span is one of the highest in the world with clearance at low water of up to 200 feet which is greater clearance than the Fremont Bridge.