In 1905, Minnesota opened a transporter bridge with a suspended gondola; the platform carried people, streetcars, and vehicles across Duluth’s harbor canal

Imagine a cold February day at the edge of Lake Superior. Two hundred people gathered on the docks at Duluth, Minnesota, to watch an engineer called Thomas McGilvray drive a massive basket through the air over the water. This enormous bridge used no wheels or cars. An entire carriage, large enough to carry 350 people, streetcars, wagons, and later cars, was suspended from a huge steel structure and moved backwards and forwards like a ski-lift on its side. According to the American Society of Civil Engineers, this was the Duluth Aerial Ferry Bridge: the world's first, and for many years the only, transporter bridge in the USA. It was an unusual design, closer to an aerial gondola than a conventional bridge, built as an engineering solution to a problem caused by the U.S. Army.

A sandbar, a canal, and a frustrated neighborhood

The roughly seven-mile Minnesota Point is the longest freshwater sandbar on Earth. It separates Lake Superior from the harbour at Duluth. In 1870-71, the city cut through Minnesota Point with a canal to allow quicker access to the harbour. This left the people living on the sandbar stranded. Duluth city officials tried to solve this issue by building a lift bridge.

According to the Minnesota Department of Transportation’s historic bridges program, the plan was rejected in 1891 due to concerns from the U.S. Army Corps of Engineers that the bridge might collapse whilst being lowered, causing problems with getting goods into one of the busiest ports on the Great Lakes. Instead, the city took inspiration from a bridge built in France in 1889, the transporter bridge over the Seine River in Rouen. Instead of a traditional lift bridge, a steel structure was built with a gondola car to transport people.

Trial run to opening day

The February crossing described at the top of this article was an early test of the structure, driven by its own engineer. The bridge then opened to the public on the first weekend of April 1905, with almost 33,000 people using the gondola within 12 hours. According to the National Register of Historic Places nomination form filed with the National Park Service, the population of Duluth was so enthusiastic about the new structure that it would be difficult to get such levels of interest in an infrastructure project in America today without a celebrity ribbon-cutting ceremony and branded hashtag. Despite the lack of modern-style fanfare, the transporter bridge worked well: it could carry fully loaded wagons, streetcars and early cars across in less than two minutes.

The limits of transporter bridges

Unfortunately, transporter bridges are not a good solution to an increasing problem. They are slow, can only carry a small amount of weight each time, and cannot scale to cope with increased car ownership. As the population of Duluth became more car-focused in the 1920s, the gondola could only carry one carload at a time and began to seem like more of a problem.

In 1929-30, the city rebuilt the bridge to create a vertical lift bridge. This was the same design that Army Corps had rejected decades earlier. The upper section of the transporter bridge was reused, which is a great example of cost-saving for a city that relies on shipping and steel.

A lasting landmark

The bridge was listed on the National Register of Historic Places in 1973 and recognised as a National Historic Civil Engineering Landmark by the ASCE in 2017. Today, as a vertical lift bridge, it still opens around 25 times a day during shipping season at what remains the largest inland port in the country. In the end, Duluth’s first solution was the flashy one, striking to look at, but impractical at scale. The dull, practical lift bridge is the one that lasted.