The zipper machine at work on the Golden Gate Bridge. (Peretz Partensky/Flickr)
Stephanie Schmidt lives in San Francisco and works north of the city, in Marin County. For years, she's had to drive across the Golden Gate Bridge twice a day, every day.
"I've been crossing that thing probably near on 10,000 times, easily," she said.
Crossing the bridge used to be a semi-terrifying experience — not just for her, but for most drivers. The lanes on the historic Golden Gate Bridge are narrow, and for decades there was very little separating the traffic heading in opposite directions — just flimsy yellow plastic tubes placed every few feet. If you happened to be driving in the center lane, it could feel like you were going to collide head-on with oncoming traffic.
"There’s a reason why it was nicknamed a suicide lane, because you were very exposed," said Schmidt.
It wasn't just terrifying for drivers, but for bridge workers, too. Several times each day, to help with traffic flow, they would move the plastic tubes to change the number of lanes in each direction. It was a fairly low-tech process.
"They had a guy hanging out of the back of a pickup truck moving the pegs," said Schmidt, "which just didn't look safe."
All that is why, just over two years ago, in January 2015, something on Schmidt's drive changed.
Now, instead of flimsy tubes, there's a big steel-and-concrete barrier. But moving a big heavy barrier like that can’t be done by a few workers in a pickup truck anymore. Now they have a special, custom-made vehicle, dubbed “the zipper machine.” (It's actually called a "barrier transfer machine," but even the bridge officials refer to it as the zipper machine, so we'll go with it.)
That zipper machine raised a number of questions for our commuter.
Is it faster for the technicians now to move the lanes? What's the etiquette of driving around those machines? Why do they have two machines? And why or what dictates when the barrier gets moved on the Golden Gate Bridge?
To answer all those questions, we went to the bridge to talk to Bill San Gregory, who supervises road services. He met us during a morning lane change, as the machine traveled across the bridge, changing the number of lanes back to the default set-up: three headed in each direction.
"Well, the machine drives along. It's already on the wall, so it just picks the wall up about 4 inches and moves it over one lane exactly," he said.
The machine isn't automated. A worker has to drive it, following blue guidelines that have been painted on the road in order to stay in a straight line. (Bonus answer: That's why there are blue lines painted on the road.)
At the front-left corner of the machine, the heavy barrier gets picked up, then it snakes through the machine, and comes out the back — moved to the right by one lane.
It can sound complicated, but it's easier to understand if you see it.
And just like that, the number of lanes in each direction has changed — and no one had to hang out the back of a truck. Plus, it's virtually impossible to have a head-on collision now; you'll just hit the barrier instead.
"It was simply a safety factor. That’s why we have that barrier," said Lisa Locati, the bridge patrol caption.
From 1971 to 2007, 16 people died from head-on collisions on the bridge. And how many have died since the new barrier went in? None, said Locati.
But it's not like this was suddenly a new problem two years ago, when the barrier finally went in. Bridge officials have actually been trying to get a moveable barrier in place since 1982.
"There was nothing that would work for our roadway because the lanes are so narrow," Locati said.
The center lanes on the Golden Gate Bridge are just 10 feet wide — whereas regular traffic lanes are usually 12 or 13 feet wide — and a regular moveable barrier is 2 feet across. That didn't leave a lot of room for cars, so something special had to be constructed.
"They designed this wall specifically for our bridge," said Locati. "It’s only one foot at its widest point."
That's how it works, but, per Schmidt's first question: Is it faster than the old system?
"By the time the guys get on the machine and start it up and do all their system checks, to moving the barrier, to then powering down the machine, it takes about an hour," said Locati. The zipper machine tops out at 7 to 8 mph.
The old system took about an hour, too, so it's actually not any faster.
And what if you drive past it while the change is happening? San Gregory said: Don't overthink it.
"Just act normal, drive right by the machine. You don't have to move or adjust your speed or anything like that," he said.
If you need to move over because the number of lanes in your direction is changing, then you'll see a big flashing traffic arrow anyway. The machine can move the barrier only to the right, which means that when it travels south into the city it's always decreasing the number of lanes traveling into San Francisco — but because it's fewer lanes from the start of your drive across the bridge, you'll always feel like you get an additional lane after you pass the zipper machine. So, you will never be driving in a lane and suddenly have it end — that would be unsafe.
You can watch this video from the company that designed the barrier:
That's also why there are two machines. When it's three lanes in each direction, there's a machine at each end, so the traffic flow could be shifted either way. But once one of the machines travels one way, then there are two machines at that end and four lanes of traffic traveling toward the machines. It could then be easily switched back to three and three.
And that brings us to Schmidt's final question: "What makes them change the lanes, because it seems really inconsistent?"
When the barrier first went in, they'd move it whenever the flow of traffic hit a trigger point -- "3,500 vehicles per lane of traffic per hour," said Locati. But drivers didn't like the inconsistency of not knowing exactly when the barrier would move.
"We realized the public wanted a more concrete schedule, so that it could be predictable," she said. For about a year now, they've been pretty set in their schedule.
Basically, they move the barrier at commute time to accommodate traffic flow. To be more specific: Every weekday around 4:30 a.m., they change to four lanes traveling into the city until 9 a.m., when they move back to three in each direction. Then on Tuesdays through Fridays, they switch to four lanes traveling in the outbound direction from 3:30 to 5 p.m. (On Mondays, traffic is lighter, so the number of lanes stays equal in each direction.)
This also sounds more complicated than it is. But overall most drivers think the zipper machine is much better than the old system -- including Schmidt.
"I like the zipper machine, because those pegs, sometimes they would miss a hole and they would just throw it, and it would be laying in the lane. And I would be terrified of running over it and popping my tire," she said.
Fear no more, Schmidt.
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