The problem was wind. Depending on conditions and direction, the wind sometimes prevented sound off the lake from reaching the pilot house over the canal’s center—a sound blind spot. The problem was addressed the following year when a “mechanical ear” was installed on the north pier .
In 1932 another near miss with a vessel prompted more safety initiatives. On June 17 the steamer Schoonmaker just missed striking the bridge, which had stopped seventy-five feet above the water when a circuit in the electric system shorted out. Operators quickly started the emergency engines and lifted clear of the steamer, after which lifting rules were changed, requiring operators to raise the bridge while the vessel was much further out in case the bridge became disabled in any way. The change allowed more time to either fix the problem or reverse the vessel. The city also purchased an electronic failure warning system. As its first decade in operation came to a close, the bridge’s lift span had raised 42,775 times.
World War II dominated the bridge’s life in the early 1940s, during which the road span’s lift total reached 56,444. Steel fueled the war effort, and iron ore came from Minnesota’s iron ranges. That ore was shipped through Two Harbors and Duluth, and each ore boat loading in Duluth came and went through the ship canal. The Twin Ports also became a major shipbuilding center. Between 1941 and 1945, the bridge lifted nearly thirty thousand times for marine traffic, averaging six hundred more lifts per year than the total average of lifts of each year from 1930 to 2005.Over the winter of 1953–1954 Duluth officials altered the method vessels used to signal the bridge to raise. Since 1930, incoming vessels signaled bridge operators with three long toots. While navigating in fog, ships traditionally gave three short blasts, but too often ship captains leaned on their horns too long in the fog, and often bridge tended misread the message and unnecessarily raised the bridge, wasting time and money and delaying traffic over the canal. Further, signals from boats calling for the aerial bridge to raise often reached the harbor’s other mechanical bridges. So beginning in the 1954 shipping season, captains of incoming vessels learned a new signal to request a bridge raising, one unique to the Duluth Aerial Lift Bridge: Long, short, long, short. The lift total for the 1950s came in at 46,736, but the opening of the St. Lawrence Seaway in 1959 increased harbor traffic—and therefor bridge lifts—in the 1960s, which witnessed 52,741 lifts.
In the 1970s, the bridge was raised and lowered 63,395times, but they weren’t all for commercial traffic. Chief operator Bob Brown explained that many of those lifts were made for pleasure craft, and the increased canal traffic was prematurely wearing down the bridge’s batteries. Brown reported that in July 1970, 1,588 vessels passed under the bridge and “552 passages were for excursion boats Flame and Flamingo.” Other small craft made 404 passages. That meant about 60 percent of all lifts were for non-commercial traffic. Further, the bridge experienced increased automobile traffic, with 119,000 vehicles crossing the bridge that June alone.
One possible solution would be to limit lifts by establishing “bridge hours”—a limit on the hours the bridge would raise for anything but “essential marine traffic.” The Coast Guard agreed. Boat owners were encouraged to take down antennas, fishing rigs, false smoke stacks, or anything else that could be easily removed to reduce a craft’s height in order to clear the bridge without requesting a lift. In 1971 the span lifted 5,873 times, 1,700 for the Flamingo and Flame—both of which, according to Brown, sported “needlessly long radio antennas and false smokestacks.” At an estimated cost to the city of $23 per lift, those two vessels alone cost Duluth taxpayers $39,000. Despite the hullabaloo, officials never put “bridge hours” into place.
In 1973 the bridge received its highest honor, a spot in the National Register of Historic Places, “primarily for its engineering qualities,” the Minnesota Historical Society reported. The bridge was one of the few non-buildings on the register at the time, joining what the newspaper called “an elite group of engineering marvels of American history.”The bridge lifted 59,986 times in the 1980s. In January 1985 city councilor Arno Kahn made an effort to bring back public bridge rides (see page 83), an idea not well received: Many believed the rides both too costly and too dangerous. In the end a warning by the state killed the idea: The bridge was about to undergo a very expensive renovation, paid for in part with state funds (see page 90–91); if the bridge was going to be used to give tourists rides, the state would withdraw its financing.
While the number of lifts dropped in the 1990s to 53,856, Park Point’s Community Club made another effort to establish bridge hours in the mid-1990s. With the Coast Guard’s consent, the bridge raised and lowered just once every half hour. The Coast Guard considered the experiment a failure, and the next summer bridge returned to lifting on an as needed basis. City officials made another failed attempt at regulating the number of lifts in 1998. After a trial lifting schedule in 2010, in 2011 the Coast Guard established that the bridge would raise every half hour between 7 a.m. and 9 p.m. between Memorial Day and Labor Day weekend. In 2018 that was extended to between March 16 and December 31.