Somewhere in a wind tunnel on the south-western side of Ontario, a group of the world’s leading bridge aerodynamics and acoustics experts are puzzling over a full-scale model of the railing of the Golden Gate Bridge.
The experts have been contracted to solve the mysterious problem of a strange humming sound that has been emanating from San Francisco’s famous bridge for the past year, driving some nearby residents to a state of madness.
The sound, heard only on windy days, has been compared to a “ghostly harmonica”, “chanting monks” and a “wheezing kazoo”.
The strange whine has quickly become a legendary piece of San Francisco’s auditory landscape. Amateur sleuths have roamed the city’s hilly streets tracking the sound’s source and an electronic music producer claimed to have mixed it into a soundtrack of existential dread.
Some fans called it the “soothing” song of the bridge. Others dubbed it “creepy” or “unbearable”. One woman simply blamed it on “aliens”.
“It sounded like a noise I could imagine jailers using to torture prisoners,” said one disturbed resident on the social media app NextDoor.
But – love it or hate it – some time this summer, according to a bridge spokesperson, the engineers will be announcing their plan to shut the sound up.
Shortly after the city’s residents began complaining of the hum in June 2020, puzzled bridge officials conducted an investigation. They followed the sound and even used instruments to measure the hum’s vibrations, finding it often emits a 440 hertz frequency, matching the musical note A.
As one poster on Nextdoor noted, you could use it to “tune your oboe”.
Eventually, the experts determined the humming occurs when the city’s voracious winds hit a set of newly installed bridge railing slats from a slightly off-kilter angle – either slightly north or slightly south of the usual winds from the west.
“After studying this phenomenon extensively, we’ve determined that the sound comes from new and more aerodynamic railing that we installed on the west sidewalk,” said bridge spokesperson Paolo Cosulich-Schwartz. “It was part of a Golden Gate Bridge retrofit designed to protect the bridge for future generations by allowing it to withstand sustained high winds up to 100mph.”
The bridge has been briefly shut down three times in its 84-year history by winds gusting to 69 to 75mph. Photograph: Jeff Chiu/AP
He said the new, thinner railing slats were installed to make sure the bridge didn’t meet the same end as the ill-fated Tacoma Narrows Bridge in Washington, which started oscillating wildly in the wind, then collapsed in 1940, shortly after it was built. That span, nicknamed “Gallopin’ Gertie”, has become a classic engineering school lesson in how not to build a bridge.
“So this was a project that we had to do,” said Cosulich-Schwartz of the Golden Gate Bridge, highway and transit district of last year’s wind resistance retrofit, which cost $12m. “With the impacts of climate change leading to more severe weather events, there was even more urgency to complete it as soon as possible.”
A study done by the agency in 2013 showed that the maximum sustained wind speed the bridge was built to endure was 69.34mph. Already, it has been briefly shut down three times in its 84-year history by winds gusting to 69mph to 75mph in 1951, 1982 and 1983. But no damage was done.
So the bridge engineers figured the new thinner slats would allow the bridge to withstand sustained 100mph winds, which the study estimated would only happen every 10,000 years. They just didn’t predict the slats would create such a cacophony in normal years.
Sustained winds of 100mph would probably come about only in a tornado or hurricane or tropical storm situation, said Warren Blier, a veteran science officer with the National Weather Service. And neither one has ever been known or predicted to hit anywhere near San Francisco.
The sound coming from the bridge, heard only on windy days, has been compared to a ‘ghostly harmonica’. Photograph: John G Mabanglo/EPA
“It seems highly unlikely to me,” said Blier, who acknowledged that his job is normally to predict weather seven days in advance, not for the next 10,000 years. “In the history of the state, no hurricane has ever hit the northern California coast.”
In the meantime, bridge engineers are determined to come up with a fix for the hum.
At the engineering company RWDI, an hour west of Toronto, a full-size model of a 12ft section of the new railing has been constructed in a wind tunnel about the size of a convention center conference room. Engineers are subjecting it to blasts of various wind speeds and testing modifications to see if they can silence the hum. The same company tested a model of the entire bridge at an earlier phase, but apparently no one realized the humming would be such an issue.
“We’ll be sharing more information about a possible solution this summer,” said Cosulich-Schwartz. “We understand that some of those who live close to the bridge have tended to find it distressing. We want to be good neighbors. So hopefully, we’ll be soothing our neighbor’s ears with a solution.”
But, in this famously opinionated city, not everyone wants to see the hum disappear. One local blogger even made a Golden Gate Bridge ambient sound playlist to help listeners on those sleepless nights when the sound is missing.
“I kind of like the sound,” said west San Francisco resident Brianne Howell, who captured a video featuring the humming bridge on one of her regular walks along the coastline. “It reminds me of the eerie sound in a movie when something creepy is going to happen. I think it’s kind of sad to get rid of it.”