Historical bridge in Duluth,MN. This bridge began as an aerial transfer bridge, the first of only two such bridges ever constructed in the United States. Originally built in 1905, the bridge was upgraded in 1930 to the current lifting design and continues to operate today. The bridge can be raised in 55 seconds and goes up 25-30 times daily during busy parts of the shipping season. The span is about 390′ long. When lifted the bridge clearance is 138′, when down the clearance is 15′.