99% Invisible
Hosted by Roman Mars
What the world's most advanced traffic system can—and can't—do for the city that invented gridlock.
5,477 words · 7 speakers
Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.
Insurance may all seem the same on the surface, but having insurance isn't the same as having State Farm. It's like getting a granola bar with a candle in it when you wanted a three-layer birthday cake. You wouldn't settle for just any dessert on your birthday. So don't settle for just any insurance. When it comes to getting the help you need, State Farm is the real deal. Like a good neighbor, State Farm is there.
Meeting new people just got way more fun because now you don't have to do it alone. With Tinder's new Double Date feature, you and your bestie can match together. Tap the Double Date icon to see profiles built for two. When two pairs match, the group chat kicks off. Scope the profiles, send memes, keep the chat fun, hype each other up, flirt a little, maybe plan a hang. It's always better when you're in it together. Try the new Tinder Double Date. Explore all the possibilities. Tinder: It starts with a swipe. Download Tinder today.
99% Invisible is presented by Acura. Curating and designing the perfect experience takes meticulous craft, an obsession with detail, and a love for innovation. Just like museum designers, Acura carefully considers every detail to curate the most engaging, exhilarating, and rewarding experience for drivers. That craft isn't always something you can see, but it's something you'll feel. That flutter in your heart, the engine roars. Every Acura is designed with deliberate intention around how people actually use the vehicles. And that is precision-crafted performance.
So we are driving around Los Angeles at the best time of day, 5:41 PM.
Vivian Lee works with me at 99% Invisible, and she's on her way out for after-work drinks at one of her favorite bars in L.A.
And my husband Cody is driving us. I'd like to say because I'm recording, but you're driving me because what?
Because you're a passenger princess.
That's exactly correct.
Some people enjoy driving. Some people, like Vivian, really do not. But nobody enjoys being stuck in traffic.
No one's moving. What are they doing? Want to burn the intersection to the ground and piss on the ashes.
Oh, my God.
L.A. is famously a car town, known for its endless freeways and its soul-crushing rush-hour traffic. And in a city full of bad intersections, Vivian and Cody are headed towards one that many consider to be the worst. It's where three roads, Fairfax, Olympic, and San Vicente, all intersect.
I think it's technically called the Fairfax asterisk, but I like to think of it as the Devil's Three Way because you have this weird triangle in the middle, and there are like one, two, three, four, five traffic lights.
To navigate this intersection, Vivian and Cody have to make it through two traffic lights in quick succession, only a couple hundred feet apart.
Oh, God.
Is it a bit caught right in the middle of...
Oh, no. We are stuck in the middle.
They make it through one traffic light, but then get stopped at the next one. And now they're stuck right in the middle of the triangle.
So there are... Oh, God. We're... Oh, boy. We are in between... Oh, my God.
I'm Delaney Hall, and this is Service Request from 99% Invisible and Campside Media. We rarely think about infrastructure until it breaks, and then suddenly, it is all we can think about. So every week, we're diving into your burning questions about the invisible systems all around us. We're exploring how infrastructure works and how it's designed and maintained. Today, traffic lights in L.A. We're looking at the system behind them, meeting the people who decide when they flip from one color to another, and trying to answer the question on every L.A. driver's mind. Why is this red light so damn long?
Oh, you son of a bitch.
The roots of LA's modern traffic system go back to 1984, when the city was preparing to host the Olympic Games. LA was expecting more than a million visitors and thousands of athletes. Traffic in LA was bad, and all these people would be flooding into a city that was already pretty maxed out. City leaders were worried that athletes and spectators wouldn't be able to make it to their events.
You're going to the 1984 Olympics in Los Angeles, and some of your friends are asking you questions. Aren't those freeways congested? Can you find your way around? What about the smog?
At this time, all of the traffic lights in LA operated independently from each other. Each one had a timing mechanism that would flip the light from green to yellow to red on a regular cadence. If a traffic light broke, or if an intersection got extra congested, engineers would likely find out about it from angry phone calls. And then, someone from the city would have to drive out to that intersection to manually reprogram the timing mechanism of the traffic light. In the process, they would often get stuck in the same congestion they were trying to fix. But the Olympics gave city engineers the motivation and the funding to try something new. With the Games looming,
a transportation official named Ed Rowey assembled a small team, and they started tinkering. And what they came up with was a network that connected 118 traffic lights around the LA Coliseum into a single system. For the first time, instead of sending someone out to every congested intersection, engineers could see what was happening across a whole area and then adjust signal timing remotely, in real time. The system went online just before the Games started.
It was an experiment, and it worked.
This is Salita Reynolds. She is the Chief Innovation Officer at LA Metro, and for eight years she ran LA's traffic light system, trying to make traffic a little bit better in one of the most trafficky cities in the world.
There are a lot of other really interesting things that happened during the 84 Games to make it such a success, but if you ask anybody who was here at the time, they will say, wow, they really solved traffic.
The first full day of Olympic competition saw a few hurdles on the massive LA freeway system. The Games not only avoided gridlock, but the sea breezes also cooperated.
And sort of famously, when the Games were over, the mayor at the time, Tom Bradley, at the closing sort of press conference said, "The Games are over. Let the traffic begin." So, you know, there was this sort of feeling that everybody had kind of made it work for the period of the Games, and now we were going to be back to our old ways.
It reminds me a little of the extraordinary measures you hear every city taking, like Beijing firing particulate into the air to make the smog, like, rain away before the crowds came for the Olympics. So it's interesting to me that, in many ways, it was one of these extraordinary measures that was taken to try to solve a problem temporarily for the Olympics, but then it continued. Why did it continue?
I think the engineers at the time were very excited by the improvements that they had seen, and they were real and measurable. They had reduced people's delay by about 30, 35%, which in turn improved emissions, right, because you didn't have as many people idling, because you were just moving the most efficient way possible.
L.A.'s success with traffic during the Olympics made a big impact. Cities planning future Olympics called them for advice. And in the years that followed, officials from Salt Lake City and Sydney and Beijing all wanted to study what L.A.'s transit leaders had built. As the system continued to expand, it got even more sophisticated, with new high-tech tools that could sense the conditions on the roads and then respond automatically.
Los Angeles is now trying to unsnarl its traffic by applying some very advanced technology. The city has begun to plant electronic sensors beneath major downtown intersections. Those sensors determine the speed and density of traffic and feed that information to a computer beneath City Hall. The computer analyzes the information and automatically operates traffic lights to relieve congestion and speed up traffic flow. We reduced delay at intersections by about 20%. We reduced stops by 35%.
By the way, that last voice was Ed Rowey, who died in 2023. When we come back, we'll learn about how L.A.'s traffic system has grown since the Olympics and why it is now known as the eighth wonder of the transportation world. That's after the break.
Sonos is a sound system engineered to make you feel. Sound is part of the design of a home, right alongside the furniture and the lighting and the art. Sonos can give ordinary rituals a little more personality. Making coffee can feel like opening credits. Dinner prep can feel like a cooking show. Or for me, I like to make it sound like a mosh pit. And tidying up can at least have a better soundtrack. Because Sonos works as a system, the mood can move with you from the kitchen to the living room to wherever the day happens next. It's not about making every moment louder. It's about making more moments feel like yours. Whatever you want to feel, Sonos can help set the scene. Every night, I play the ambient sleep music channel on the Sonos in my bedroom, and it helps me relax, it helps me sleep better.
The Sonos is on almost 24 hours a day when I'm not recording. Love the sound, feel the system. Visit sonos.com to build your system.
T-Mobile has an exclusive bundle for customers 55 and up. I'm Sarah Bull. Yeah, I'm Frank Bull.
Reliable network is key for us. And with T-Mobile, it's been wonderful. And going to the 55-plus plan saved us so much money.
A lot.
And that's important, trying to keep costs down. The home internet's been perfect. It's fast, it's quick. The setup was so easy, it took less than 15 minutes.
It was like, "Ah!" If you want simplicity, coverage, reliability, you want the whole package, T-Mobile has it. Right now, T-Mobile customers 55 and up can get two phone lines on America's best network. Plus, America's fastest 5G home internet for just $30 each.
$30 per month each line with autopay plus taxes and fees. Minimum age 55. Pricing for home internet rely on two lines of essentials. Choice 55. $35 connection charge per line required. Best mobile network and fastest 5G home internet based on analysis by Oklahoma Speed Test Intelligence Data, 2H 2025. All rights reserved.
Insurance may all seem the same on the surface, but having insurance isn't the same as having State Farm. It's like getting a granola bar with a candle in it when you wanted a three-layer birthday cake. You wouldn't settle for just any dessert on your birthday. So don't settle for just any insurance. When it comes to getting the help you need, State Farm is the real deal. Like a good neighbor, State Farm is there. Meeting new people just got way more fun because now you don't have to do it alone. With Tinder's new Double Date feature, you and your bestie can match together. Tap the Double Date icon to see profiles built for two. When two pairs match, the group chat kicks off. Scope the profiles, send memes, keep the chat fun, hype each other up, flirt a little, maybe plan a hang.
It's always better when you're in it together. Try the new Tinder Double Date. Explore all the possibilities. Tinder, it starts with a swipe. Download Tinder today.
Since 1984, the small, scrappy system that started with the Olympics has grown into one of the most sophisticated traffic management operations in the world. Today, it's known as ATSAK, Advanced Transportation System and Coordination. And it controls almost all of the city's 5,000 traffic signals. And while it would be malpractice to say that the system has solved LA's traffic issues, it has made traffic a little... Little less bad. Believe it or not, without this system, the streets of LA would be even more clogged. The way it works is that there are sensors buried in the pavement at most intersections
across the city, and they count cars as they pass. The sensors feed a constant stream of data back to a control room in downtown LA where engineers can watch a live map of LA traffic. When a street starts to back up, the system automatically responds. It can extend a green light, or make one shorter, nudging timing across the whole system of intersections to help traffic flow more smoothly.
And there are traffic engineers, transportation engineers, and planners and other folks that are sitting in an office in downtown Los Angeles. They have hundreds of cameras that give them basically a 360-degree view of the city at any time. And they also have a landscape view of what's happening with every single transportation signal at all of the 5,000-plus intersections that they're monitoring at any given time.
So these various signals run into ATSAQ, which I am imagining as sort of the NASA Mission Control Center. Is that what it looks like?
Kind of, yes. Houston, we have our truck. It is number 128.
Selena told me the ATSAQ control room has become legendary among traffic nerds, and it's been featured in a couple of movies, including a 2003 heist film called "The Italian Job."
We're moving out.
There's this scene where someone hacks into the ATSAQ system to create a huge traffic jam in the middle of LA. We're locked on.
We've crashed. It's not a crash. We've got power.
I can't log in.
And there's a shot of the ATSAQ control room in the movie with engineers holding their heads in their hands, staring at these enormous screens that show intersections across the city. They're totally freaking out as cars smash into each other and traffic descends into chaos.
So in that control room, you're saying it's a mix of technology and human intervention to make the signals change. So in some cases, there's a person pressing buttons, flipping switches, and making the lights change?
They can do that in extraordinary circumstances. So when I first got to Los Angeles, there was actually a giant sinkhole that opened up in the ground over by UCLA. Less dramatic than that, there's spontaneous protests or other things happening. At that point, they're making decisions about, okay, we're going to leave this light on green for longer and clear people out of a space when they need to be redirected or rerouted.
But these are mostly extraordinary circumstances. For the most part, it sounds like there are computers that are making decisions about when to flip from green to yellow.
Yeah, think about the way that we're managing movement through a city. You know, we're managing it in space and time. And the space is limited, right? We have 7,500 miles of streets in the city of Los Angeles. So there's a lot, but we have what we have. It's fixed. So that congestion that you experience, that's too much demand for a fixed amount of space.
I like this idea that traffic engineering is all about space and time, because it elevates what seems like a mundane discipline into something a little more epic. The space part is pretty simple. Basically, every car, bus, bicycle, and pedestrian is competing for the same fixed space on the roads. And the reality is that engineers cannot do much to expand that space. But they can work with time.
And that's where their special algorithms come in. There is so much data collected from those sensors embedded in the pavement. And it reveals stuff like rush hour patterns and holiday surges and what a Wednesday on the road looks like versus a Sunday. And the algorithms crunch through all that information and then translate it into precisely timed traffic lights.
For the most part, those algorithmic sort of calculations for how much green time one street gets versus the other and that balancing, it's pretty fixed by the time of day and the day of the week and so on and so forth. But there are moments when unpredictable things happen and the sensors have a certain amount of intelligence and they're able to perceive those changes and reallocate things in real time. And then sometimes the system becomes so strained that it breaks and you have to have a human in the loop to intervene and actually manage it manually. And that human needs to be connected to all of the other humans that are there to make things work.
But to move this many cars and this large of a system that has this much complexity and variation, you have to have all of those things at the same time.
That sounds like this increasingly sort of brain breaking math problem. Like how you synchronize across that many signals and how you make this intersection flow smoothly without creating chaos in an intersection somewhere else. That sounds so hard.
It is. And it's also, we're talking about people's lives, right? That's one of the reasons why people love transportation is because it has such an immediate effect on people's lives. And so part of what you're also doing is Trying to figure out the tolerance that exists across the system for delay or frustration. And so you're having to sort of consider how pain is being spread around. And you're having to sort of accept that in order to balance things, everybody has to share the pain a little bit. And you're also making a judgment call. So on the main drag, there may be, let's say,
forty five or fifty thousand people a day that are driving on that main street. On the cross streets, you have a much smaller number of people. And so you're going to privilege the greatest good for the greatest number, right? You're going to privilege the fifty thousand people on the main line. And the people on the side streets are going to experience more pain because they're going to have to wait a little bit longer. But eventually you're going to get to go.
Right. What I hear you saying is that it's collective. And there's also something a bit utilitarian about it.
Yeah. And that goes for everybody who's using the street, right? People biking and walking as well. If there's a bus, right, that's coming along or a train that needs to make it across the street, there's a lot more people moving much more efficiently in the train or on the bus or even on a bike, taking up a lot less space, which again is one of our most precious resources. And so figuring out how to, how to balance safety, efficiency, delay and the sort of quality of people's lives are all the ingredients that have to go into the creativity with which the system gets managed.
Yeah, it's interesting to think about this as it's this highly engineered system. There's algorithms, there's lights, there's wires. But ultimately it is about people's time. It's actually very human.
It is. I consider it as much of an art as it is a science. You know, when we move a little white line on the street, you know, six inches this way or six inches that way, we know that it changes how fast people drive or how they behave. And so it's a lot more about human behavior than it is about.
A math equation.
Yeah, exactly.
When we come back, 99PI producer Vivian Lea visits the ATSEC control room. Once she's there, she hacks into the system and screws up traffic across LA in order to facilitate the movement of a huge amount of stolen gold. Just kidding. She just wants to figure out what's up with her least favorite intersection, the Fairfax asterisk. That's when we return.
T-Mobile has an exclusive bundle for customers 55 and up.
I'm Sarah Bull. Yeah, I'm Frank Bull. A reliable network is key for us. And with T-Mobile, it's been wonderful. And going to the 55-plus plan saved us so much money. A lot. And that's important, trying to keep costs down. The home internet's been perfect. It's fast, it's quick. The setup was so easy, it took less than 15 minutes. It was like, "Ah!" If you want simplicity, coverage, reliability, you want the whole package, T-Mobile has it.
Right now, T-Mobile customers 55 and up can get two phone lines on America's best network, plus America's fastest 5G home internet for just $30 each. $30 per month each line with autopay plus taxes and fees. Minimum age 55. Pricing for home internet rely on two lines of essentials. Choice 55. $35 connection charge per line required. Best mobile network and fastest 5G home internet based on analysis by Ookla of speed test intelligence data 2H 2025. All rights reserved.
Insurance may all seem the same on the surface, but having insurance isn't the same as having State Farm. It's like getting a granola bar with a candle in it. When you wanted a three-layer birthday cake, you wouldn't settle for just any dessert on your birthday. So don't settle for just any insurance. When it comes to getting the help you need, State Farm is the real deal. Like a good neighbor, State Farm is there.
Think GLP-1s are too expensive? On Ro, you can access FDA-approved GLP-1 weight loss treatment at your lowest possible price if you're covered. Start with Ro's free insurance
Just upload your insurance card to see if you're covered for certain GLP-1 shots. Whether you use insurance or pay cash, Ro helps you find an option that works best for you. Plus, Ro's membership plans help you save even more. See if you qualify at ro.co/health. Rx only. For side effects of GLP-1 medications, including boxed warning, go to ro.co/safety. Additional Ro membership fee required. Meeting new people just got way more fun because now you don't have to do it alone. With Tinder's new Double Date feature, you and your bestie can match together. Tap the Double Date icon to see profiles built for two. When two pairs match, the group chat kicks off. Scope the profiles, send memes, keep the chat fun, hype each other up, flirt a little, maybe plan a hang. It's always better when you're in it together. Try the new Tinder Double Date.
Explore all the possibilities. Tinder: It starts with a swipe. Download Tinder today.
Hi, good morning. Hi, good morning. The ATSAAC Control Room is located in downtown LA in a huge glass building around the corner from City Hall. It's a big space that looks kind of like a corporate meeting room with blue-gray carpet and a wall of glass windows where you can see traffic down below. But the main attraction is the huge block of screens that stretches across the front of the room. It displays live camera feeds of intersections across the city so that engineers can keep an eye on where congestion is building up and why it's building up. The cameras show me why it's congested. This is Eric Zambon, a transportation engineer in charge of the ATSAAC Center.
He gave Vivian a tour last month and talked her through the big screen and what it allows the engineers to see. Is there an emergency vehicle that's blocking a lane, causing congestion? Or is there even a crash in the middle of the intersection? And at that point, we jump on our system and we would modify signal timing parameters to best help people get around those locations. Gotcha. On that same big screen, there's also a map of every traffic signal in LA. They show up as multicolored dots of light. So that's the graphic of all the traffic signals. Every dot is a node or a traffic signal, and that's our signal network.
This shows in real time. Status of the signals in the city. Every color represents something to us. And although it just looks like a Christmas tree to some people, it tells us the operation of the signals just at quick glance.
We're looking at, you know, the layout of Los Angeles, mostly green. Could you explain to me, like, what patterns you see? When you look at this, what does this actually mean to you?
Okay, so green means it's online, good communication. It's running a cycle length. Right now, we're coming up on just past the AM peak traffic period. All right, so things are starting to slow down. As Eric explained, most of the traffic lights were working well, and they were running their usual timing. As the cars start to congest, it ramps up the green time to help provide throughput to get people through that area. So these are the smartest. The ones with the pink in the middle are the smartest intersections that we operate.
Could I ask you about one intersection in particular that really grinds my gears?
Of course, are you from LA?
I am from LA. It's pretty close to me. Do you know what the Fairfax asterisk is?
Uh, that's Olympic Fairfax San Vicente?
Yeah.
Yeah, so that was designed well before we had our current...
Eyeballs.
Yes, it's so bad, and there's nothing I can do about that. We've viewed that through the lens of 50, 60 years of traffic. We have put that into traffic signal modeling software. We've done everything we can, and I hate to say this, but the confluence of three major streets during peak hours leads to nothing but frustration, and signal timing can't fix it. And we just inherited that very bizarre, geometrically bizarre intersection that has traffic signals, and we have to assign right away two different streets going east-west and one going north-south. And it's proven to be a very difficult thing. I don't know that it'll get better.
Do you feel like you have to kind of just do what you can with, like, the mess that you've been given?
That's exactly how I feel, yeah, yeah. I'm only laughing because you described... Describe what goes on in my mind every day.
It's that space-time problem again, as Salita Reynolds described it. The ATSAQ system has improved traffic in LA, but it can't control the fundamental layout of the streets or the number of people using them. It can't control the fact that LA was built as one of the most car-centric cities in the world. Engineers can play with time, coaxing millions of people through various bottlenecks. But sometimes, no matter how advanced their algorithms, it's still kind of lipstick on a pig. And they're still left with something like the Fairfax asterisk, an intersection that just was not designed to handle so many cars.
So I just want to understand sort of how much what we've learned about ATSAQ might apply to another city. So if someone's sitting at a red light in another city, you know, Des Moines, Miami, how much of what's happening is basically the same? And how much is really unique to the ATSAQ system itself?
A lot of other cities will have maybe part of the city on a connected traffic management system. And most other major metropolitan areas will have a centralized traffic management center, where there'll be the same kind of setup. There'll be some cameras, there'll be some video. But it's usually for some subset of their city, some smaller, you know, maybe it's the downtown and it's a sort of a smaller scale kind of place where things are being managed. And so it is a repeatable sort of blueprint that has become kind of state of the practice.
OK, and then finally, another Olympics are coming. It's 44 years after ATSAQ was born.
Is it going to play a similar role this time around? Is it going to expand again?
Yes, absolutely. It's going to play a similar role and we have some more tricks up our sleeve in terms of what does ATSAK 3.0 look like for the 28 games? And how can we make sure that we're moving the trains and the buses and keeping people on foot safe and getting around by bike or scooter? One of the most fun and attractive ways to do so.
Well, thank you so much, Salita. It was really fun to learn about this system. We really appreciate having you on.
Yeah, my pleasure.
We're about to go through the intersection.
Back at that terrible intersection, Vivian and Cody are waiting.
We're just sitting at a red light, so this might be a lot of dead air for a while.
Someone's crossing this intersection on roller blades.
Are they crazy?
In the dark, too.
In the dark?
But pretty soon, the light changes and they start to move.
Okay, we are turning left on Fairfax. Here we go. Oh, green lights. Oh, boy. All right, that's it. Not so bad, right?
That wasn't so bad.
Not the worst traffic we've ever been in.
We started with the question, how do LA's traffic lights actually work? And the answer is that the whole city is wired up. There are sensors embedded in the pavement at many traffic lights, and they connect through miles of underground fiber optic cables to a centralized control room. In that control room, engineers monitor traffic flow and make adjustments in real time. It's a system that started very small when Ed Rowey and his team faced this impossible task, which was to keep traffic moving smoothly during the 1984 Olympic Games. And since then, the system has grown and ATSAK now manages nearly 5,000 traffic lights at intersections across the city.
With that, consider this service request resolved.
Today on the show, you heard Salita Reynolds, the Chief Innovation Officer at LA Metro, and Eric Zambon, a transportation engineer in charge of the ATSAK Traffic Management Center for LADOT. You also heard Vivian Le, supervising producer at 99PI, and her husband, Cody Franklin. We're going to go to our pub now.
Bye.
What infrastructure mystery keeps you up at night? Is there something in your life that you use every day, but you don't actually understand how it works? Submit your service request by recording a voice memo with your question and emailing it to [email protected]. And remember, the next time you're stuck in traffic and you are cursing the lights, know that somewhere there's an engineer who has spent years trying to steal back seconds on your behalf, one green light at a time. I'm Delaney Hall. Infrastructure is everywhere, and we are here to help you decode it.
Service Request is a production of 99% Invisible and Campside Media. The show is produced and fact-checked by Julia K. Slavine and edited by Shoshi Shmulevitz. Mix by Ewen Lai Trumewen. Theme song and music by Swan Real. Show arts by Aaron Nestor. Roman Mars is our boss at 99PI. Kathy Tu is 99PI's executive producer. Matt Share is the executive producer at Campside. We are part of the SiriusXM Podcast family. You can find us on all the usual social media sites as well as our Discord server. There's a link to that, as well as every past episode of 99PI at 99pi.org.
Page updated October 31, 2026 · transcript and summary are machine-generated
