You’re sitting at a red light, tapping your fingers on the steering wheel, maybe checking the clock because you're running five minutes late. It's a universal experience. But have you ever actually wondered about the person who decided that red means "stop" and green means "go"? Most people think there’s a single name—a lone genius in a workshop—who solved the chaos of early 20th-century traffic. The truth about who created the stop light is actually way more complicated, a bit more dramatic, and involves a gas-lit explosion that almost killed a guy in London.
History is rarely a straight line.
🔗 Read more: YouTube TV Set Up Explained: What Most People Get Wrong About Switching to Streaming
Before cars even existed, cities were nightmares of horse-drawn carriages, bicycles, and confused pedestrians all fighting for the same ten feet of dirt road. It was total mayhem. If you want to get technical, the first attempt at a traffic signal happened in 1868 in London, near the Houses of Parliament. A railway engineer named J.P. Knight took the "semaphore" system used on trains—those big mechanical arms that flip up and down—and stuck it on a pole. At night, it used red and green gas lamps.
It worked. Sorta.
Then it exploded. A gas leak caused the whole thing to blow up in a policeman's face, and London decided maybe traffic lights weren't such a great idea after all. They didn't try again for decades.
The Men Who Tamed the T-Model Ford
Fast forward to early 1900s America. Henry Ford’s assembly line started pumping out cars like crazy, and suddenly every intersection in Detroit and Cleveland was a death trap. This is where the debate over who created the stop light really heats up because three different men hold a piece of the crown.
First, there’s Lester Wire. He was a Salt Lake City detective who, in 1912, got tired of seeing his colleagues standing in the middle of intersections dodging carriages. He built a wooden box with a slanted roof—it looked like a birdhouse—and dipped light bulbs in red and green paint. He didn't patent it. He just wanted to save lives. People actually mocked him for it. They called it "Wire’s birdhouse" and would purposely ignore it.
Imagine being the guy who invents the future and everyone just laughs at you.
Then came James Hoge. In 1914, he installed a system in Cleveland at Euclid Avenue and East 105th Street. This was a big deal. It was the first "electric" signal that actually used words. Instead of just colors, it had "STOP" and "MOVE" lit up. It was connected to a switch inside a little booth where a police officer sat. If an emergency vehicle was coming, the officer could flip a switch and clear the path.
Garrett Morgan and the Three-Way Revolution
If you went to school in the U.S., you probably heard that Garrett Morgan is the answer to the question of who created the stop light. He is a massive part of the story, but not for the reason most people think.
Morgan didn’t invent the "stop" or "go."
📖 Related: Why What is a Test Still Confuses Everyone in Tech and Education
What he did was realize that the jump from "Go" to "Stop" was terrifyingly dangerous. In the early 1920s, signals just flipped instantly. One second you're cruising, the next second the cross-traffic is T-boning you. After witnessing a horrific carriage accident in Cleveland, Morgan realized we needed a "warning" position.
He patented a T-shaped pole with three positions. It wasn't just on or off; it had a neutral state that stopped traffic in all directions so people could clear the intersection. This is the ancestor of our yellow light. Morgan was a brilliant businessman and an African American inventor who faced immense systemic hurdles. He eventually sold his patent to General Electric for $40,000, which was a fortune back then.
Why Red, Green, and Yellow?
It feels natural now, doesn't it? Red is blood, danger, stop. Green is... well, what? It wasn't always that way.
The colors actually come from the maritime and railroad industries. Originally, railroads used red for stop, white for go, and green for caution. You can see the problem immediately. A white light at night could be anything—a streetlamp, a house window, or a star. In one famous (and tragic) railway incident, a red lens fell out of its lantern, leaving the white bulb exposed. The engineer thought it was a "go" signal and crashed.
The industry pivoted. Green became "go" and yellow became "caution" because it was the most distinct color against the others.
- Red: High frequency, stays visible through fog and dust.
- Green: Highly visible contrast to red.
- Yellow: Picked because its wavelength is close to red but distinct enough to signify a transition.
The William Potts Contribution
We can't talk about who created the stop light without mentioning William Potts. He was a Detroit police officer in 1920. While others were working on two-color systems or manual arms, Potts decided to use railroad lights to create the first four-way, three-color traffic light.
He didn't patent it.
Because he was a government employee, he didn't think he could. That’s why you don’t see the "Potts Signal Company" on every street corner today. He basically gave his invention to the world for free. Detroit became the testing ground for the modern grid we know today. By 1920, the city had 15 of these towers.
The Evolution of the "Brain" Inside the Light
Early lights were dumb. Honestly, they were just timers.
If you were sitting at a light at 3:00 AM with no one around, you just had to wait for the clock to tick down. That changed with Charles Adler Jr. He was an eccentric inventor who thought, "Why can't the car tell the light it's there?"
In 1928, he invented a "sonic" detector. You literally had to honk your horn to make the light change. Can you imagine the noise in a modern city if we still did that? Neighbors hated it. Eventually, we moved to pressure plates in the road, and now we use inductive loops (the wires you see buried in the pavement) or cameras with AI to detect vehicles.
What Most People Get Wrong
The biggest misconception is that there is "one" inventor.
If you say "Garrett Morgan invented the stop light," you're technically wrong, but you're also right about his contribution to the safety interval. If you say "Lester Wire did it," you're ignoring the fact that his version was basically a home DIY project that didn't scale.
History is a relay race.
- J.P. Knight (1868): The gas-powered failure that proved we needed something.
- Lester Wire (1912): The first electric two-color attempt.
- James Hoge (1914): The first municipal electric system.
- William Potts (1920): The three-color, four-way setup.
- Garrett Morgan (1923): The patented three-position safety signal.
How to Spot the History in Your Own City
Next time you’re driving, look at the lights. You can actually see the evolution of this technology if you know where to look.
Most modern lights are shifting to LEDs. They don’t burn out as often, but they have a weird side effect: they don't get hot. In snowy cities like Chicago or Minneapolis, the old incandescent bulbs used to melt the snow off the lens. With LEDs, the snow just piles up until the light is invisible. Engineers are literally having to add heating elements back into the "high-tech" lights to fix a problem we solved in 1920.
Also, look for the "Opticom" sensors—those little black tubes on top of the light. They’re looking for a specific strobe frequency from ambulances. It’s the high-tech version of James Hoge’s 1914 manual switch.
Practical Takeaways for the Curious Mind
If you're researching who created the stop light for a project or just because you’re a trivia nerd, here is the nuance you need to sound like an expert:
- Specify the Type: Are you talking about the first gas signal (Knight), the first electric signal (Wire/Hoge), or the first three-color signal (Potts)?
- Acknowledge Garrett Morgan: His contribution wasn't just a light; it was a system of safety that General Electric used to standardize traffic across the country.
- Check Local History: Many cities claim they had the "first" light. Usually, they just mean they were the first to buy a specific patent.
The stop light wasn't an "Aha!" moment. It was a desperate response to the chaos of the industrial revolution. It was born out of blood, literal explosions, and a few guys in Cleveland and Detroit who were tired of seeing horses and cars smash into each other.
✨ Don't miss: When Was the Machine Gun Invented? The Messy History of Rapid Fire
To dig deeper into this, check out the patent records for Garrett Morgan (U.S. Patent 1,475,024) or look into the Detroit Historical Society’s archives on William Potts. You'll find that the "simple" red light is anything but.
Actionable Next Steps:
- Audit Your Commute: Notice the sensors at your local intersections. If you see a line cut into the asphalt in a square shape, that’s an inductive loop based on the tech Charles Adler Jr. pioneered.
- Verify the Sources: If you're writing a paper, don't just credit one person. Reference the transition from the 1868 London gas-lamp to the 1923 Morgan patent to show a complete understanding of the timeline.
- Support Local Museums: Many "first" traffic lights are housed in local history museums, like the Henry Ford Museum in Dearborn, Michigan, which holds an original Potts signal.