New Jersey drivers complain about traffic the way other people complain about weather: constantly, specifically, and with the quiet assumption that nobody outside the state could possibly understand how bad it really is. This summer gives the state a fresh and very public excuse, since MetLife Stadium, temporarily renamed New York New Jersey Stadium because FIFA doesn't allow sponsor names anywhere near the World Cup, is hosting eight matches over six weeks.1 Officials are planning to move more than 78,000 spectators per match through the Meadowlands using a coordinated network of shuttle buses, rail service, and rideshare drop-offs, with no general parking allowed at the stadium at all.2
Underneath all the complaining about Jersey traffic specifically is a genuinely hard, genuinely interesting computer science problem, one that's been quietly evolving for over a century, and it's worth taking seriously for a second before going back to complaining about it.
The problem existed before the technology did
Traffic lights weren't invented because someone thought intersections needed decoration. They were invented because cities were, in the words of one 1920s report, "unbearable, unendurable, uncontrollable."3 By the early 1920s automobiles had started outnumbering horse-drawn wagons in major cities, and the resulting mix of cars, streetcars, pedestrians, and horses all fighting for the same intersections at the same time produced exactly the chaos you'd expect.4
The earliest fixes were entirely human. A traffic officer stood in a booth or a tower and manually flipped switches or waved semaphore arms.3 It worked, sort of, but it scaled terribly, since it meant a dedicated person at every busy corner in a growing city, all day, making judgment calls under pressure with no way to coordinate with the officer at the next intersection over.
The shift toward automation came from a Detroit police officer named William Potts, who in 1920 built the first four-way, three-color traffic signal, adding the amber light specifically because he was frustrated that police at different intersections couldn't change their lights at exactly the same moment.5 He attached a timer to coordinate it. The economic case for doing this was immediate and enormous: automating signal timing in New York City let the department reassign all but 500 of its 6,000 traffic officers, saving the city an estimated $12.5 million.5
That's the first version of the core tradeoff this whole post is actually about. A human directing traffic can react to what's actually happening in front of them, but doesn't scale. A timer scales effortlessly across an entire city, but has no idea what's actually happening in front of it. Nearly every advance in traffic engineering since 1920 has been an attempt to get the responsiveness of the first approach without losing the scalability of the second.
Why a fixed timer alone was never going to be enough
For decades, that's basically all traffic lights were: fixed interval timers, running the same preset schedule regardless of what traffic actually looked like at any given moment.6 This is precisely why it's possible to sit at a red light at 2am with zero cross traffic in sight and just wait anyway. The signal isn't responding to reality. It's running a script written in advance, based on average conditions, applied uniformly whether it's the dead of night or the exact moment 78,000 World Cup fans are all trying to leave the Meadowlands at once.
The first real attempt to make signals actually sense the world came in the 1950s. In 1952, Denver installed a single computer that controlled 120 traffic lights citywide, fed by six pressure-sensitive detectors that measured inbound and outbound traffic, with the entire control room housed in the basement of the City and County Building.7 By the 1960s, cities like Toronto were running even more advanced detection across 159 signals through ordinary telephone lines.7 The 1970s introduced vehicle sensors directly into the pavement itself, which finally let signals adjust their timing based on whether anyone was actually there, rather than running the exact same plan at 3am and 3pm alike.8
What it actually takes to make a light "smart" today
Modern adaptive systems are the direct descendants of that 1950s Denver experiment, just dramatically more capable. Sensors at intersections and along corridors continuously monitor traffic volume, speed, occupancy, and queue length, using inductive loops embedded in the pavement, video detection cameras, radar, or data pulled directly from connected vehicles.9 An adaptive system detects a heavy queue building in one direction, extends the green light for that approach, and shortens it for the less busy directions, continuously, rather than running the same fixed plan all day regardless of what's actually happening.9
That alone is already a meaningfully harder problem than it sounds like, because it means weighing competing demands in real time. Extend the green for the backed-up direction too long, and the side street that was previously moving fine now backs up instead. Every adjustment at one intersection changes the conditions feeding into the next one down the road, which is exactly the kind of problem that gets harder, not easier, as you add more intersections to coordinate.
The part that's genuinely elegant: green waves
Here's the concept that made me actually respect traffic engineering as a discipline, and it's older than you'd think. New York City pioneered synchronized traffic lights as early as the 1920s, building systems that coordinated signal timing across multiple intersections at once so vehicles could move smoothly along major streets without stopping at every block.10
When a series of intersections coordinate their timing so a driver moving at the expected speed hits green light after green light continuously, it's called a green wave.11 The signal phases and periods across multiple lights get chosen specifically so that a stream of traffic can flow continuously through several intersections in a row, typically along one or two directions.11
This only works under certain conditions. Green waves are most effective when traffic velocity is relatively constant, and when most traffic is heading in the same direction at the same time, which is exactly why a perfectly synchronized green wave during a normal Tuesday afternoon commute can completely fall apart the moment something abnormal happens, like, for instance, tens of thousands of soccer fans converging on a single stadium from every direction at once. There are real mathematical constraints on achieving full coordination across all directions simultaneously, which means a system tuned for smooth north-south flow during rush hour has to make tradeoffs that get exposed the instant traffic patterns change.11
This is, fundamentally, a distributed coordination problem. No single intersection has full visibility into the entire network's state. Each one makes local decisions based on local sensor data, while ideally still contributing to a coherent pattern across the whole corridor, which sounds a lot like the kind of distributed systems challenge that shows up constantly in software, just with the added twist that a wrong decision here doesn't throw an error, it throws an extra fifteen minutes onto someone's commute.
Why this summer is the system's actual stress test
Officials are well aware that this particular stress test is coming. The coordination plan for World Cup matchdays spans NJ Transit, the Port Authority, the MTA, the New Jersey Department of Transportation, the New Jersey Turnpike Authority, and Amtrak, all working together to move spectators in and out of a stadium that explicitly will not allow general parking on its own property.2 Rail service to the stadium will run on a matchday-only schedule, requiring fans to transfer through Secaucus Junction, while regular commuters not attending matches get rerouted through entirely different paths just to avoid colliding with the surge.12
It's worth pointing out that the actual cost of moving all these people has become its own minor political dispute, with the state pushing back on FIFA over who foots a roughly $48 million transportation bill for the event.2 Whatever gets decided, the underlying engineering challenge doesn't change: a transportation network tuned for ordinary commuting patterns has to absorb eight days, spread across six weeks, of wildly atypical demand, concentrated at one location, arriving and leaving within tight windows around kickoff.12
Modern adaptive traffic systems are explicitly designed to flex with real-time conditions instead of running a fixed script, which is exactly the kind of flexibility a one-off mass event actually needs.6 But there's a meaningful difference between handling the normal daily variance of a commute and handling a sudden, massive, geographically concentrated spike that doesn't match any pattern the system has tuned itself against before. Sensors and adaptive algorithms can react to what they're currently seeing, but a green wave optimized for typical traffic flow doesn't automatically know what to do when typical stops applying for one Saturday afternoon, eight separate times, between June and July.
Why New Jersey drivers are right to complain, just maybe not for the reason they think
The instinct to blame "Jersey traffic" specifically, as if the state has uniquely bad luck or uniquely bad drivers, misses the more interesting truth: this is a hard coordination problem everywhere, with a hundred-year history of incremental fixes, each one solving the limitation of the last one while introducing a new one. A timer fixed the scaling problem an officer couldn't solve. A sensor fixed the responsiveness problem a timer couldn't solve. A green wave fixed the single-intersection myopia a lone sensor couldn't solve. And a sudden, massive, atypical event is exactly the failure mode none of those previous fixes were built to anticipate.
New Jersey just happens to be running one of the more demanding live versions of that century-long problem this summer, with one of the densest, most interconnected transit and roadway systems in the country trying to absorb an unusually concentrated load. It is, in the end, the same basic problem any distributed system runs into under unexpected load: a network that's well-tuned for its normal traffic pattern gets stress-tested the moment something abnormal and large arrives all at once, and the seams show up exactly where the system wasn't designed to flex. New Jersey is about to find out, eight times, over six weeks, exactly where those seams are.
Footnotes
1 On MetLife Stadium being temporarily renamed for the 2026 World Cup and the match schedule. ABC7 New York: Take a tour of New York New Jersey Stadium
2 On the regional mobility plan, spectator volume, and the transportation cost dispute with FIFA. ROI-NJ: World Cup Host Committee and NJ Transit Announce Regional Stadium Mobility Plan
3 On the urban chaos that prompted the invention of automated traffic signals in the 1920s. OPTraffic: The Evolution of USA Automatic Traffic Light Signal Timing
4 On the rise of automobile traffic in the 1920s and the resulting safety problems at intersections. EBSCO Research Starters: Traffic Signals Invented
5 On William Potts's 1920 four-way, three-color traffic signal and its economic impact on New York City's police department. Wikipedia: History of Traffic Lights
6 On the limitations of fixed-time traffic signal systems compared to adaptive ones. Omnisight: What Is Adaptive Signal Control and How Does It Improve Traffic Flow
7 On the 1952 Denver computerized traffic control system and Toronto's 1967 telephone-line-based signal network. Wikipedia: History of Traffic Lights
8 On the introduction of vehicle sensors in the 1970s, enabling real-time signal adjustment. OPTraffic: The Evolution of USA Traffic Lights in the Past Century
9 On the sensors and real-time decision-making behind adaptive traffic signal systems. Eltec: Adaptive Traffic Signal Control Systems Explained
10 On New York City's early synchronization of traffic signals across multiple intersections in the 1920s. OPTraffic: The Evolution of USA Automatic Traffic Light Signal Timing
11 On the concept of green waves and the mathematical constraints on coordinating traffic across multiple intersections. arXiv: Self-Organization in Traffic Lights
12 On the specific matchday rail service adjustments and rerouting for World Cup 2026 at MetLife Stadium. NJ Transit World Cup: Commuters
