The History and Meaning of Colored Traffic Lights

Traffic lights might be the bane of bottlenecking traffic in the inner city. This is especially true if it seems like you’re just hitting the reds all the way to work. But let’s face it, the traffic light provides that extra layer of safety.

Thanks to the traffic light, we’ve managed to associate colors with responses. Red with stop or danger, amber with caution, and green with go. But who conceptualized those colors in the first place?

The Origin of the Traffic Light

Prior to automated traffic lights, pedestrians, bicycles, street cars, horses, and motorcars made for dangerously chaotic congestion.

When Was the First Traffic Light Installed?

The first traffic light invented was in London in the 1860s, but it was hardly recognizable—or effective. It had been adapted from the railroad signal system by a railway manager, John Peak Knight, in 1868. The railroads used red gas lights at night to signal stops and green gas lights during the daytime. Knight installed a similar gas light, semaphore system near London’s Westminster Bridge in December of 1868. 

The life of the first traffic light signal was short-lived. A gas leak caused one of the signal lights to explode on its police officer operator within a month of being installed. It took 40 years for the United States to adopt the system, albeit with better safety standards.

The First Traffic Lights in the United States

In the early 1900s, the first types of traffic lights stuck with the semaphore design, which used moving arms to indicate the “stop” and “move” commands. These were popular in cities such as Chicago, where traffic was on a sharp rise.

San Francisco adopted the red and green colored lights of the railways, and it also introduced the first automatic option.

The History of The Yellow Traffic Light

In Detroit, the running of red lights became a glaring problem. There were simply too many cars, horses, and carts on the road to safely bring traffic to a halt. A policeman, William Potts, designed the first three-way and four-way colored traffic signs. This allowed for an extra signal, proceed with caution, to be displayed. This design was adopted in future traffic light designs across the world.

Traffic direction used to require police officers to stand in busy intersections.

The 1920s saw traffic lights pop up at major intersections across the United States and Europe. Bustling roads and bottlenecking traffic caused delays. They were also becoming increasingly dangerous for pointsmen.

Birdhouse traffic light designs and manually operated electric ones were some of the early designs. The race was on to find a solution to the increasing traffic problem. Europe was especially hard hit as the infrastructure was not designed to accommodate motorcars. Think cities like Milan and Paris, which still have traffic problems to this day.

The First Traffic Light Patent

In 1923, inventor Garrett Morgan designed an affordable, modern solution to the traffic light. It would irrevocably change the manufacturing process of traffic lights. The T-pole design meant that it was visible and safe. He registered the patent in Canada and Great Britain, too.

Automatic Light Changes

A microphone that was programmed to trigger a switch when it picked up upcoming traffic was popular for a while. This was until motorists simply honked their horns to get the green-all-the-way. The lights had to be reprogrammed to only change after a 10-second period after the first change to avoid accidents.

Modern-Day Traffic Lights

It’s not something you think about every day, but have you ever wondered how the traffic light changes when you’re pulling up a quiet intersection? The traffic lights rely on sensors that tell it that cars are approaching. Traffic lights are programmed to give the right of way, which is essential to proper flow, especially in busy city intersections. 

Adaptive traffic control systems are already making a mark in cities such as Pittsburgh, where wait time at intersections is believed to have dropped by 40%. The system relies on video feed and makes autonomous, real-time decisions based on the traffic flow at any given time. This is all done with the help of artificial intelligence (AI).

Apart from railway and industry heritage, traffic lights also follow an international standard. Well, mostly. The Vienna Convention on Road Signs and Signals Treaty encourages countries to sign a treaty. Countries such as the United States of America and Japan haven’t signed the treaty, so slight deviations from the international standards might occur. 

Green Traffic Lights

Here’s a quick rundown of what green lights mean:

• Solid Green: We know green as go. A green light means you may proceed through the intersection. However, pedestrians and cyclists need to pass through the intersection first. If you happen to be turning left, you need to yield to traffic that’s moving straight through the intersection. 

• Green Arrow: The green arrow allows you to turn into the intersection once it’s cleared of pedestrians, cyclists, and other traffic. When the traffic light is red for oncoming traffic and you have a green light, you don’t need to yield. 

So why are green lights, well, green? Green has a shorter visual wavelength, which means it’s easy to spot. We also inherited the green light from the railways, as it happened to be an easy color to spot at night. 

Before that, white was used to signal “go” and green “proceed with caution,” but this proved disastrous as the white light was easily confused with stars and other lights. Since then, green has become a symbol of movement and getting the “go ahead.”

On a more technical side, the green light isn’t fully green. It often contains blue bulbs to help those with colorblindness. The green light has also evolved across the world from the standard solid color to arrows, even flashing ones. Unless you’re going to Japan, that is, where blue is the standard.

Yellow Traffic Lights

Yellow lights can be more confusing for drivers! Here’s what they mean:

• Steady Yellow: This light tells us that the signal is about to turn red. If you’re already in the intersection, proceed with caution. However, if you’re not in the intersection yet and it’s safe to stop, then do so. 

• Flashing Yellow: This light indicates that you may enter the intersection, but proceed slowly and with caution. 

• Steady Yellow Arrow: Approach the intersection with caution, as there may not be enough time before the light changes. You may proceed through the intersection once it’s clear. This signal is not used in all states. It’s important to know that oncoming traffic may have the green light, as this is a permissive traffic light.

• Flashing Yellow Arrow: This is a fairly new addition to traffic lights and has been introduced to certain cities in New York, Texas, and California. This is a permissive signal which allows motorists to proceed through the intersection without stopping, but yielding to oncoming traffic and pedestrians. It’s followed by a steady yellow arrow or a steady green arrow.

An interesting fact is that the timing of the yellow determines its efficacy in preventing an accident. A stretch of road that has a 45 mph speed limit should not have the same timing on the yellow light as a road with a 55 mph speed limit. The higher the speed limit, the longer the transition from green to yellow to red. 

If the timing is under, it might cause rear-ending and the running of red lights. Considering that more than 20% of traffic accidents occur at intersections, this timing is essential in curbing accidents. 

Traffic centers across the world are tasked with finding the sweet spot where deceleration can take place safely. Busy city centers, for instance, should have different timing in place than a road on the outskirts of the city that doesn’t see much traffic. 

Red Traffic Lights

Red is a pretty clear signal to stop. But there are different variations. Here is what they mean:

• Steady Red: A steady red light means you need to come to a complete stop. If you cross the intersection after the light turns red, you risk endangering others and yourself. You may also get a ticket, as running a red light is considered a traffic violation. Most states allow you to make a right turn after a complete halt if the intersection is clear. 

• Flashing Red: Flashing red lights need to be treated like a stop sign. Motorists should not sit and wait for the green light, but rather, proceed on their way as soon as the coast is clear.

• Red Arrows: A red arrow that’s not flashing may also be treated as a stop sign in some states. In other states, the car should come to a complete halt until the light changes to green. Also, refer to your state driver’s handbook to ensure you’re following the rules of that particular state. 

• Flashing Red Arrows: A flashing red arrow indicates you need to stop before proceeding to take your turn when safe to do so.

Stay Safe With Traffic Light Knowledge

Traffic light meaning is fairly consistent across the board and various deviations. Green means it’s safe to proceed (though you should still exercise caution). Yellow means caution and yield. Red means danger and stop. Always drive defensively and obey traffic signals.

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Updated 12/13/2021