“Red means stop, green means go” is a traffic rule common around the world. But few know that in the past, it was not always green for go, red for stop, and yellow for caution. Let’s explore the history of traffic lights that not everyone knows in the article below.
The History and Future of Traffic Lights
Why do we stop at red and go at green instead of the other way around? Why not choose other colors besides red and green? To find the answers, let’s go back to the 1830s.
The Origin of Traffic Lights
The current color signaling regulations for traffic originated from a system used in the railroad industry in the 1830s. At that time, railroad companies developed a signaling system for train operators to know when to stop or continue. Each color represented different actions: red signified stop, white indicated go, and green was a cautionary color.
Modern signaling post in the railroad industry
The reason red, the color of blood, was chosen as a danger signal dates back to ancient times. Some historians suggest that Roman legions used red flags as symbols of the god of war in battles over 2000 years ago. Clearly, red is an effective color for signaling to stop due to its high visual impact. However, using white to signal go created several issues.
For instance, in 1914, an accident occurred because the red filter had fallen off, exposing the white bulb inside. The signal operator thought the system was functioning normally, while the train driver saw the white light and assumed it was safe to proceed. As a result, the train collided with the car in front. In response to this situation, the railroad industry decided to change green to signify “go” and yellow was selected for caution. The railroad industry believed that the three colors—red, yellow, and green—were distinctly different and easily recognizable by the human eye.
How was the Signaling System Adapted from Railroads to Roads?
In 1865, in London, England, concerns arose within the community due to the rapidly increasing number of horse-drawn vehicles, which posed dangers to pedestrians crossing the streets. At that time, an engineer and railway manager named John Peake Knight, who played a vital role in designing the railway system in England, approached the London police and proposed the idea of using the semaphore signal system from the railways to regulate normal traffic.
Traffic signal post proposed by John Peake Knight in 1868
Semaphore Signal.
According to John’s idea, the traffic signal would have one or more arms that could be raised and lowered horizontally to block the road. During the day, police officers would control it to signal horse-drawn vehicles when to stop and pull aside. At night, the post was equipped with red and green lights to inform drivers when to go or stop. This event marked the transition of traffic signals from railways to regular roadways.
Soon after, John’s proposal was quickly accepted, and on December 10, 1868, the first signal post was installed at the intersection of Great George and Bridge Street in London. The system worked effectively… until a few months later: one of the gas pipes supplying the lights leaked. Unfortunately, the police officer controlling the post did not notice the gas leak, resulting in the bulb exploding and the officer being burned. Therefore, despite its initial success, the traffic signal post was immediately discontinued in England.
The Development of Traffic Signals in the United States
Traffic towers used in several countries in the 1910s
Across the ocean in the 1910s and 1920s, police in the United States also used tall towers to oversee traffic more effectively. During this time, officers could use the green and red lights from the railroad system to signal vehicles when to go or stop. Another method involved officers waving their arms to control traffic.
In 1920 in Detroit, Michigan, a police officer named William L. Potts invented a four-faced, three-color traffic signal, using all three colors—red, yellow, and green—to control traffic at intersections. This marked Detroit as the first city in the world to use a three-color traffic light system, which is still widely applied today. Following this, numerous inventors continued to redesign various traffic light models, some retaining the three-color system while others opted for different colors. At that time, traffic signal posts required a person to operate the switch, press buttons, etc., to change the light colors. Naturally, the costs of implementing and operating traffic lights through this method were quite high.
William L. Potts’ four-faced, three-color traffic signal model
By the late 1920s, some automatic traffic lights began to be invented. The first model simply changed light colors at specific time intervals. However, the drawback of this method was that some vehicles had to stop while no vehicles crossed the intersection. At that time, an inventor named Charles Adler Jr proposed an idea to address this issue.
Adler invented a traffic light system that could detect car horns. A microphone was installed at the intersection of two roads. When a vehicle stopped, all the driver needed to do was honk the horn to change the traffic light. To prevent drivers from continuously honking and causing rapid light changes, Adler stipulated that once the light changed, it could only change again after 10 seconds. He believed this time period would allow at least one vehicle to safely cross the road. Of course, this system also caused significant annoyance for pedestrians and nearby households due to the constant honking.
Inside a traffic signal control center in the 1970s
At the same time, inventor Henry A. Haugh proposed a new traffic light system to address previous shortcomings. Haugh’s system utilized two metal strips to detect when a vehicle approached. When a vehicle passed over and made the two metal strips come into contact, the light would soon change color to allow the vehicle to continue moving forward. However, Haugh’s model revealed a flaw: in some cases, vehicles did not pass over the required point, causing the light change system to malfunction.
It wasn’t until the 1950s, with the development of computers, that traffic light color changes saw significant improvement. Traffic lights began to operate more accurately and quickly. In 1952, 120 traffic lights in Denver were controlled by computers. Following that, in 1967, the cities of Toronto and Ontario officially adopted dedicated computer systems to control traffic signals. Not long after, computer systems were able to manage traffic signals in 159 cities across the United States via telephone lines. At the same time, operators could quickly adjust the timing of green and red lights using computers.
Over time, traffic regulation via signals has become increasingly refined thanks to advancements in technology and computer support. Although methods may vary, green, red, and yellow remain the three primary colors used for traffic signals in most countries worldwide.
The Future of Traffic Lights: Adding a Fourth Color, Integrating AI?
Modern traffic lights have 3 colors. (Photo: Shutterstock).
Different colors, sometimes flashing, have the best effect on the human brain, while self-driving cars operate better with a single light.
Professor Ali Hajbabaie at North Carolina State University (NCSU) is leading a team designing a traffic system related to autonomous vehicles.
As a result, it is very likely that white will be the fourth color added to traffic lights as self-driving cars become more prevalent. The white light will be understood by autonomous vehicles as a directive to “proceed unless otherwise instructed.”
Despite various types of traffic signal technologies, most traffic light systems fall into two categories: fixed-time signals and adjustable-time signals based on traffic flow.
Professor Henry Liu at the University of Michigan has proposed a different approach to addressing traffic congestion using artificial intelligence (AI). Liu and his team are experimenting with using real-time speed and location data from vehicles equipped with Global Positioning System (GPS) to adjust traffic lights. They are conducting tests in the suburb of Birmingham, Michigan.
Professor Liu explains that there is no need for information from cameras or sensors to adjust traffic flow, meaning that traffic lights can receive information solely from vehicles to make adjustments without any external intervention.
