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Why are traffic lights Red, Yellow and Green?

Published Thursday, October 27, 2005

Color is a silent language that affects our behavioral response in our daily lives. It can also be a learned response that can cause us to respond in a certain way based on our cultural background. For example, what would you think of a man in a pink outfit, underwear or shoes? A learned response is also responsible for the color preferences that we have through our experience of past events in our daily social life. A behavioral response on the other hand happens naturally without us being aware of it. For example, the color red can heighten our perception of danger just by seeing it - the color of blood. It can also cause sensations of excitement and warmth - which is a color used to express love such as valentines day and the red heart to represent love. Nevertheless, with regards to the traffic light, we all know that from our everyday experience - a learned response - that a red light means “STOP“ (and I really have to assume this since some people always fly across this red light at traffic intersection to the detriment of others), a yellow ( or amber) light means “ SLOW DOWN” - approach with caution and prepare to stop while green light means “GO” - if it is safe to do so. This weeks article will answer the question above and don’t go feeling that you know or have the answer (idea) to this question based on what you just read!

How It All Started

The colors used by automobile traffic light system was originally adopted from the color code system used by railroad engineers as a traffic signal devised to control the trains on the railroad. This color system was used on railroads to prevent fatal train collisions and thus this traffic signal device was implemented to reduce train collisions by providing trains with advance warning of danger.

The first choice of color that was selected to be used by the rail road engineers to represent a stop signal was the color red. This color - the color of blood - was selected because it symbolizes danger or warning thus, it was logically the most likely choice to get the attention of anyone. It sends the message that if ignored, there could be very serious consequences such as serious injuries or death. Therefore this color was selected to symbolize the signal stop.

For the other two colors, railway traffic light being a new system at the time, railroad engineers experimented with the colors green which was the color for "caution" and white (clear) which was the color for "go". However, in the 1830s, these traffic signals lights were colored by using red, green and clear filters. Due to the use of these filters some very serious train collisions would occur. This problem would stem from the fact that the street lights, distant stars, glare of the sunlight and other lights could easily be mistaken for the “go” light. In addition to this, sometimes the red filter of a "stop" traffic signal would fall out leaving the bulb emitting white light which in a sense would be signaling the message “go”. To correct this problem engineers made modifications where red light would be the signal “stop”, yellow light “caution” and green “go”. This move solved the problem of filters falling out. Whenever a white light signal is seen this indicates that something is wrong with its signal lamp and it needs to be corrected right away.

Traffic officials during the horse and buggy days, were facing heavy traffic in big cities which put great pressure on police officers who had to be stationed full time directing traffic at busy intersections. In addition to this, the situation was about to become worse with the coming of automobiles. Due to the fact that the railroad traffic color system worked so well with the railroad system, it was readily adopted for automobile traffic light system. This adoption came through a police officer name William Potts of Detroit, of Michigan. He came up with an idea to rectify this problem by using the railroad traffic signal system. This he achieved by using the same scheme of colors of the railroad traffic and using wires and electrical controls to make the world’s first 4-way three color traffic light. This was installed in Detroit (on the corner of Woodward and Michigan Avenues) in 1920.

During this time, African American Garrett Augustus Morgan (1877-1963), seeing the need of a control traffic flow invented the electric automatic traffic light. This was installed in Cleveland, Ohio in 1914 and had only two lights: red and green. However, the yellow light was added after the need for a "caution" light became crucial for the traffic signal to serve its purpose effectively. This set the foundation on which modern four-way traffic lights are built.

Garrett Augustus Morgan also invented the gas mask, in the early 1900s which was used by firemen and also by soldiers in World War I.

Did you know?

Color blindness
In order to help support people with red-green color blindness, red light contains some amount of orange in its hue, and the green light contains some amount of blue. This helps to identify the red and green light.

Related Articles:
How Rainbows Are Formed - What Causes a Rainbow?
The Meaning of Colors - Color Symbolism
Why leaves change color in fall?
What causes hair to turn gray?
Why do people have different colors of skin?
Why is the sky blue?

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Thats pretty interesting info....

The "Did you know?" part was the best... I didnt know there was orange hue to that red light...

Great stuff!

Now I can ask all my acquaintances tomorrow the same question (and let them think I'm a genius)! :D

Take care and have a great weekend!

Rather than color, wouldn't it be simpler to use alphabets instead? That would overcome the color blindness bit Enviroman Says

hi there...
came to know about your blog from amstaffie.

i must say the write up is great! so thats the origin for the colours!!

Cool. I never knew. Now can you please tell me how to get out of a completely bogus traffic ticket? I swear to G-D I didn't run that light!

Did you know that your very informative blog is currently "Blog Of Teh Day" at Teh Blogfather's corner? ;-)

Bubble Boy:

Thanks for visiting and I am thankful that you learn something here : )


Thank you for your compliment. Glad that I could help there : )

You have a great weekend also!


Very good reasoning there however, the alphabet would have to be universal and our letter of the alphabet are not the same for all countries. Color is universal in spite of one’s language or origin. Also, the letter sign would have to be very large (which might not be feasible for its size) to help those who specially suffer from shortsightedness! - another problem has a rise : )


Welcome! Thanks for the compliment and the visit : )

Genetic lorax:

Thanks for your comment and visit.

I wish I had the answer to that one : )

Teh Blog father:

Thank you for my site being blog of the day!!! I am so honored!!! Thanks also for the recent review and also for spicing it up with your sense of humor. I can never repay you for your kindness however, I will be providing a link to your site.

Thanks again, it is greatly appreciated : )

R. Edmondson:>Thank you for my site being blog of the day!!!

No worries. You have great content on there, so it's only right :-)

R. Edmondson:> I can never repay you for your kindness however, I will be providing a link to your site - so I am part of the family now!!

Good man. As soon as I can track your link via Technorati (I know you are on it) I'll add you to the family list.

PS: if you can use the "Approved By Teh Blogfather" image, that would be awesome.

Most people are impatient with traffic lights. When the road seems clear and the green light takes time in flashing, impatient drivers just go without the signal.
And in Nigeria, we only understand the "Red" and "Green".

Great post...sometimes, the red light does look more orangy than normal...and some green lights are quite blue-green.

The color red being the caution light makes sense, since the color red invokes certain emotions in us...it's a striking color.

Here's a quick "Did you know" for "Did you know"...Researches have found that atheletes that wear a uniform that's predominatnly red has a higher winning percentage than teams that wear other colors?

The color red is vivid, and can make an athlete seem more aggressive, and makes the athlete feel more invincible.

Tiger Woods used to wear red only on Fridays, but now he wears a red shirt all the time.

thanks for yr interesting topic to share with us ... wooof

Teh Blogfather:
An "Approved By Teh Blogfather" image could be added but at the moment I am finding creative ways to free up a lot of images and links on my right column. If I do find some way to add this creatively, then it will be done :)

Too often traffic signals are ignored which lead to serious casualties. Most drivers in these accidents are not color blind.

Thanks for that “Did You Know” info. :) very interesting indeed. Another example of how color affects our behavioral response.

Thanks for the visit and the compliment :)

Great site! I'll have to show it to my kids.



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Stephen Stapinski

Really your blog is very interesting.... it contains great and unique information. I enjoyed to visiting your blog. It's just amazing.... Thanks very much for the share.

Now I know where the colors on the traffic light came from. Well, we should be thankful to the person who created the traffic light cause without him, I'm pretty sure we are all be suffering from many traffic violations and road accidents. I must say, you've got an interesting topics for your blogs and it's been very enlightening.

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