By Thomas K. Pendergast
To many people, it sounds as though – under the right wind conditions – the Golden Gate Bridge is singing, humming, whistling or playing the world’s biggest harmonica. Some people like the sound; some hate it. But many agree that the new sound is loud. Really loud.
Terry Trevino lives in San Francisco and commutes across the bridge to Marin regularly.
“I think it’s probably one of my downfalls, is that I definitely have sensitive ears and I was trained as a musician most of my life, and because of that I think I’m just quite sensitive to the sound,” Trevino said. “And I have to say, going across it as it’s ‘singing,’ it’s incredibly loud. It’s desperately loud, almost to the point where it’s debilitating if you’re really sensitive to sounds.”
Trevino lives on Lone Mountain and was in his home when he first noticed the noise. At first he thought it was a street cleaning truck, but it kept going. So then he thought it was a carpet cleaning machine operating somewhere in his neighborhood.
“I’m on the upslope of Lone Mountain,” Trevino said. “Our house and our land is literally tilted toward the bridge. That may be one reason why,”
And the sound just went on and on and on.
“It literally went on all day long,” he said. “It’s like when you get a bunch of metronomes in the room and they all play at the same time, you get all of them playing together.”
The noise has been heard since the installation of a “suicide deterrent” net which is strung up under it to try to dissuade people from jumping off the bridge to their deaths.
The noise can also be attributed to structural engineering measures designed to make the bridge more stable in high winds.
As it stands now, the bridge is only rated to handle sustained winds of 68 mph, according to Paolo Cosulich-Schwartz, spokesperson for the Golden Gate Bridge Authority. For quite a while, plans have been in place to bump that up to at least 100 mph.
“The project was necessary, and we were going to do it before the suicide deterrent system was approved and construction started on that project,” Cosulich-Schwartz said. “It was only made more urgent and necessary because of the suicide deterrent. We are adding quite a bit of metal to both sides of the bridge as part of that suicide deterrent project and the wind retrofit will ensure that the bridge will maintain its structural stability.
According to Cosulich-Schwartz, engineers predict that the metal net under the bridge will pick up the wind and act like a big, long sail, pulling on the bridge with a pressure that the iconic structure was never designed to handle. So, new railings and fairings, which are structures added to increase streamlining and reduce drag, are being installed on the west side of the bridge to deflect the wind from the roadway in the hope that this will counteract the extra drag produced by the west winds blowing on the net.
The new railings are located along the west sidewalk between the towers. As of late July, their installation was about 75% complete. These new railings are the source of the sound, resonating under certain wind conditions much like the reeds of a giant harmonica.
Just below the new railings, are wind fairings.
“That’s a metal, quarter-arc circle that sits just below the sidewalk, that is designed to deflect wind up and above, over the sidewalk and roadway to insure that the bridge can withstand sustained high winds without risking its structural stability,” Cosulich-Schwartz explained. “That work is happening a little slower. It started later than the installation of the railings, so that is about 10% complete.”
He is well aware that the newest siren of San Francisco is getting mixed reviews from the locals.
“We’ve received some concern from community members about the sound. We’ve also received feedback that people enjoy it and find it pleasing or meditative or a curiosity that they are really enjoying amid news stories that are rather grim,” he said. “We are studying it further to better understand precisely how the sound is being created and in what specific conditions, because it happens infrequently, only when the winds are very high and, we understand, from specific angles. We’re studying it more closely to understand the exact effect, so that we might be able to look at implementing measures that might dampen or eliminate the noise.”
He admits, however, that they might not be able to cut the noise if they want to keep the net. On the other hand, it seems that only certain conditions, like extremely powerful winds coming in from the west at an angle to the bay, can make the bridge sound like a giant harmonica.
“We don’t know the specific angles but it looks like it happens when there’s a little north or a little south to the strong westerly winds,” he said.
Cosulich-Schwartz also acknowledged that the district studied the impacts of the project, including wind tunnel testing of a scale model under high winds, and that those tests, as previously reported in other media, showed the bridge “would begin to hum” when air passed through, describing this as “a known and inevitable phenomenon.”
But he later walked that back a bit.
“There were no indications from the testing or the analysis that we did that it would create the sound that we heard starting in early June,” he said. “There were people that thought something like this could happen, but no one thought that it would make the level of noise that it did. So it wasn’t revealed in any studies or tests. There were predictions that something like this could happen, but it was a limit of the testing that we were doing that this wasn’t revealed.”
They did several wind-tunnel tests with scale models of the bridge using different materials “and at that scale, it’s not the same as having tons of steel out suspended over the windy entrance to the bay. There’s no substitute. We don’t understand the mechanics fully yet.”
Categories: Golden Gate Bridge