I love photographing bridges and learning about their history, so it's no surprise that there are quite a few photographs of the iconic aerial lift bridge in Duluth, Minnesota, among my collection of Midwest travel photos.
This bridge in the heart of the city's downtown area is a landmark in Duluth and featured prominently in the city's official logo. The bridge is arguably one of the most photographed sites in the state and earned a spot on the National Register of Historic Places in 1973.
There is some argument about the bridge's uniqueness according to what I've read, but even if lift bridges are not unique, they are not all that common. Several examples of lift bridges exist in Europe and in New Jersey's Meadowlands, and Midwest Guest readers may remember my recent story about the Portage Lake Lift Bridge at Houghton-Hancock in Michigan's Keweenaw Peninsula.
Duluth's lift bridge moves traffic over a small canal cutting through the five-mile-long Minnesota Point (a.k.a. Park Point) sand bar. The canal, constructed in 1870-1871 to accommodate boat traffic, created an island separated from mainland Minnesota. Ferries moved residents, visitors, and goods across the gap in warmer months, while a temporary footbridge strung across the water moved traffic across the ice during the colder months.
Increasing traffic made the ferries and the swinging bridge suspended across the gap inadequate. The densely populated area made building many conventional types of bridges requiring long approaches impossible, so the city sponsored a contest in 1892 to find the best design.
John Alexander Low Waddell designed the winning idea, a span conceived as the world's first high-rise vertical lift bridge. However, the city scraped Waddell's design (which Chicago eventually used for a now-defunct bridge at South Halstead Street), and City Engineer Thomas McGilvray redesigned it as a gondola bridge.
The newly redesigned bridge, completed in 1905, had the now-familiar steel arch, and a suspended gondola with a capacity of 60 tons. The gondola could carry 350 people, plus wagons and horse teams, street cars, and other vehicles. The crossing took about a minute, with as many as a dozen trips per hour scheduled during the day and two trips per hour during late-night hours.
The gondola transporter bridge proved inadequate by the late 1920s, and engineers turned back to Waddell's original idea for an aerial lift bridge.
Engineer Claude Allen Porter Turner reconfigured the design to eliminate the gondola and incorporate a lift span into the existing steel framework. Other modifications included extending the side towers and moving bridge operators from the gondola to a control house at the center of the span.
The upgrade began in 1929, and the bridge first lifted its center span to allow for passing boat traffic the next year.
It takes about three minutes to completely lift the span, although it takes as long as 15 minutes to lift and lower the bridge for larger ships because the lift starts when the boats are three miles away. The bridge averages 25 to 30 lifts a day during the summer shipping season
A system of storage batteries, generators, concrete weights, and electronic pulleys power the bridge. Even so, the bridge can occasionally become stuck as it did in July of this year when a lightning strike created a two-plus-hour delay for car traffic when the bridge stalled in the up position during a busy evening rush hour.
Check out this web cam link to see the bridge in action.
Want to learn more Duluth's Aerial Lift Bridge? Check out Crossing the Canal: An Illustrated History of Duluth's Aerial Bridge by Tony Dierckins or this Duluth Aerial Lift Bridge DVD celebrating the bridge's 2005 centennial.
© Dominique King 2010 All rights reserved