Aerial Lift Bridge - Bridge History

Bridge History

The bridge spans the Duluth Ship Canal, which was put through the thin but long sand spit named Minnesota Point (commonly referred to as Park Point by locals) in 1870–71. The natural mouth of the St. Louis River is about seven miles (11 km) farther southeast, and is split between Minnesota and Wisconsin. Creating this gap in the tiny peninsula meant that residents who lived on the new island needed to have a way to get across. Several different transportation methods were tried, though they were complicated by the weather. Ferries could work in the summer, but ice caused problems in colder months. A swinging footbridge was used, but was considered rather rickety and unsafe.

In 1892, a contest was held to find a solution. The winning design came from John Low Waddell, who drew up plans for a high-rise vertical lift bridge. The city of Duluth was eager to build the bridge, which would have been about 130 feet (40 m) wide. However, the War Department objected to the design, and the project was canceled before it could be built. Waddell's design went on to be built in Chicago, Illinois as the slightly larger South Halsted Street Bridge (removed in 1932).

New plans were later drawn up for a structure that would ferry people from one side to the other. This type of span, which is known variously as an aerial transfer, ferry, or transporter bridge, had first been demonstrated in Bilbao's Vizcaya Bridge in 1893 and one in France in 1898. Duluth's bridge was inspired by the one in France, though the actual construction is quite different. The architect was a city engineer, Thomas McGilvray.

When it was completed in 1905, the Aerial Bridge's gondola had a capacity of 60 short tons (54 tonne) and could carry 350 people plus wagons, streetcars, or automobiles. A trip across the canal took about one minute, and the ferry car moved across once every five minutes during busy times of the day. However, a growing population on Minnesota Point, a greater demand for cars, and an increase in tourism soon meant that the bridge's capacity was being stretched to the limit.

A remodeling was planned that would remove the gondola and incorporate a lifting platform into the structure. Ironically, the firm finally commissioned with designing the new bridge was the descendant of Waddell's company. The new design, which closely resembles the 1892 concept, is attributed to C.A.P. Turner. Reconstruction began in 1929. In order to ensure that tall ships could still pass under the bridge, the top span had to be raised to accommodate the new deck when raised. The support columns on either side were also modified so that they could hold new counterweights to balance the weight of the lifting portion. The new bridge first lifted for a vessel on March 29, 1930.

The bridge can be raised to its full height in about 3 minutes, and goes up 25 to 30 times daily during busy parts of the shipping season. The span is about 390 feet, or 120 meters. As ships pass, there is a customary horn-blowing sequence which is copied back. Long-short-long-short means to raise the bridge, and Long-short-short is a friendly salute.