You're sitting at a red light on a Tuesday morning, probably late for work, tapping your fingers on the steering wheel. It’s such a mundane part of life that we don't even think about it. But have you ever wondered who made the stoplight?
If you ask a history textbook, you might get one name. If you ask a proud Clevelander, you’ll get another. The truth is, the traffic signal wasn’t some "Eureka!" moment in a lab. It was a desperate, messy response to the absolute chaos of early 20th-century streets. Imagine horses, early Fords, streetcars, and pedestrians all fighting for the same inch of mud and cobblestone. It was a bloodbath.
Before we had the three-color electric glow we know today, the world’s first "stoplight" was actually a terrifying explosion waiting to happen. In 1868, a guy named John Peake Knight set up a gas-lit signaling tower outside the Houses of Parliament in London. It used semaphore arms—basically big wooden planks—to tell horse carriages what to do. At night, it used red and green gas lamps.
It lasted about a month.
Then it leaked, exploded, and seriously injured the police officer operating it. London decided they were better off with the chaos, and the idea of a "stoplight" basically went dormant for nearly fifty years.
The American Chaos and the Rise of Garrett Morgan
Fast forward to the early 1900s in America. Detroit was cranking out cars. People were buying them faster than the government could pave roads. There were no lanes. No speed limits. No stop signs.
By the 1920s, the intersection was the most dangerous place on earth.
This is where Garrett Morgan enters the frame. Morgan was a brilliant Black inventor in Cleveland who had already made a name for himself with a "safety hood" (an early gas mask) and hair-straightening products. Legend has it that Morgan witnessed a horrific carriage-and-auto collision at an intersection. He realized the problem wasn't just "stop" and "go."
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The problem was the transition.
In 1923, Morgan patented a T-shaped signal. It didn't have lights; it had positions. But here was the genius part: it had a "third position." Before this, signals just flipped from GO to STOP instantly. Morgan’s device allowed the whole intersection to pause, giving everyone time to clear out before the other side started moving. It was the mechanical ancestor of the yellow light.
Morgan eventually sold his patent to General Electric for $40,000. That was a massive sum back then. GE took his "all-stop" concept and integrated it into the electric systems they were developing.
Wait, What About Lester Wire and William Potts?
If you're looking for who made the stoplight in its electric form, you have to talk about Salt Lake City and Detroit.
Lester Wire was a detective in Salt Lake City in 1912. He was tired of seeing his fellow officers standing in the middle of freezing intersections, waving their arms like madmen. He built a wooden box with two colored lights—red and green—and dipped the bulbs in paint. He mounted it on a pole and ran it off the overhead trolley wires. People hated it at first. They used to pull over and yell at the "birdhouse" because they didn't want a machine telling them when to drive.
Then there’s William Potts.
Potts was a Detroit police officer. In 1920, he took the red, green, and amber lights used by railroads and figured out how to make them work for street traffic. He’s often credited with the first actual four-way, three-color traffic signal.
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Wait. Why did he use red, green, and yellow?
It wasn't random. We owe that to the shipping and railroad industries. For centuries, red has meant danger. It has the longest wavelength in the visible spectrum, meaning you can see it from further away, even through fog or rain. Green originally meant "caution" on railroads, and white meant "go."
That caused a lot of deaths.
Sometimes the red lens on a railroad signal would fall out, leaving the white bulb exposed. An engineer would see the white light, think it was the "go" signal, and plow straight into another train. Eventually, they shifted green to "go" and brought in yellow for "caution."
The Evolution of the "Smart" Signal
The stoplight didn't stay a dumb timer for long.
By the late 1920s, an inventor named Charles Adler Jr. came up with a signal that responded to sound. If you wanted the light to turn green, you had to honk your horn. This was hilarious for about five minutes until residents living near intersections realized they were living in a permanent cacophony of car horns.
Thankfully, we moved to pressure plates. You might remember these from the 90s—those big rectangular cuts in the asphalt near the stop line. These were induction loops. Basically, when a big hunk of metal (your car) sits over the loop, it changes the magnetic field, telling the computer "Hey, someone is waiting here."
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Today, it's all about computer vision and AI.
In cities like Pittsburgh and San Francisco, companies like NoTraffic are installing sensors that don't just "see" cars, but can tell the difference between a bus, a cyclist, and a pedestrian. If a group of kids is walking to school, the AI can actually hold the red light longer to make sure they get across safely.
Why the Invention of the Stoplight Actually Matters
It’s easy to dismiss this as "just a box with lights," but the stoplight changed the shape of our world. Without it, the "suburban dream" couldn't exist. You can't have millions of people commuting into a city center every morning if the intersections are blocked by five-way fender benders.
It also created a new kind of social contract. Think about it. We all agree to stop our 4,000-pound machines just because a little red bulb tells us to. It’s one of the few times every single day where we all collectively agree to follow a rule for the sake of the person next to us.
Garrett Morgan’s contribution, specifically, was about empathy. He didn't just want traffic to move; he wanted the "little guy"—the pedestrian and the horse-drawn carriage—to have a window of safety.
How to navigate the history of the stoplight
If you’re researching this for a project or just a bar bet, here’s how to categorize the "inventors" so you don't get corrected:
- The First Concept: John Peake Knight (1868, London). Gas-powered, exploded.
- The First Electric Two-Color: Lester Wire (1912, Salt Lake City). Hand-painted bulbs.
- The First Four-Way Three-Color: William Potts (1920, Detroit). The railroad adaptation.
- The Essential Patent: Garrett Morgan (1923, Cleveland). Introduced the "all-stop" interval that led to the yellow light.
The next time you’re stuck at a red light that feels like it’s lasting an eternity, remember William Potts and Garrett Morgan. It beats dodging a runaway horse and carriage in the middle of a muddy Detroit street.
Actionable Insight: If you feel like your local traffic lights are timed poorly, you don't have to just complain. Most city planning departments take public feedback on signal timing. You can actually request a "Traffic Engineering Study" for a specific intersection. Modern "smart" signals often need recalibration as traffic patterns change after new construction or school openings. Check your city's Department of Transportation website for a "Request for Service" or "Signal Timing" form.