Why is red color used for "STOP" traffic signals and green color used for "GO" traffic signals?

Red color is the color of blood which can heighten our perception of danger just by seeing it, so 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.

Green color is a reassuring color in most cultures, and has a strong emotional correspondence with the idea of safety.

Green is the color of nature, growth, harmony, freshness and fertility.

Red color has the longest wavelength in the visible spectrum so we can see it from a distance especially if it was raining or full of dust or mist.

Yellow and green comes after red in order from longest wavelength to shortest wavelength.

Red color can be seen from far due its reflection and can detect by human eye any weather condition that’s was why it has been chosen for danger, so human can see and do the needful.

I believe green and yellow has chosen due to its representation in nature, for example green trees etc and yellow is sign of mild danger as we see human face yellow, we start to believe some wrong with person, or may be he sick.

by physics, wave length matters, as red is more hot and of shorter wave length so penetrate more and travels more in air ( i.e. can be seen from far distance) while green wave length is longer so travels less ( i.e. seen from short distance) simple isn't it ?

Because the red color can be seen afar for so it is clear enough for all.

But green color is suitable for its bright where the cars are near.

red color signal means to warning the drivers from dangers, so red sign for me is to stop from getting  accident. 

green color signal for me means your out of danger and ready to go... well,  that's my theory sir Salah. 

red naturally signifies danger, from experience when dealing with violent situations you notice common tell tale signs, one being the colouring up of the skin in the face like a "blushing" as the body forces adreneline and oxygenated blood cells to the major motor regions preparing to fight or flight. this is the body language telling its oponent "i am charged and i am ready!!" 

  this is a standard warning sign identified under the conflict resolution model use by the majority of western police forces .. next time someone is in heated argument just watch thier "blushing" as they are becoming more aggitated also accompanied by clenching and un clenching fists and changing stance.

There is something call a colors temperature meter goes by the name of Kelvin "K" based on the name of the founder  Lord Kelvin (William Thomson).

colors start from the HOT colors until it reaches the COLD colors in another word it start from RED till it reach the Dark BLUE, and these colors interfaces with our Vision and Physical actions.

the RED color usually present danger or such and thats for our eyes can catch RED colors easily.. and most of the warning sign goes with that color.

the GREEN is deep and gives a feelings of calm and piece and comes in the middle of the colors temperature... needless to say that Green is a mix between Yellow and light Blue.. but Yellow comes after RED in the Colors temperature scale, and it interfaces with our caution.. that for its also in the streets light.

RED also signifies for Danger or ALERT.....to be careful before moving I mean STOP

GREEN color signifies growth, prosperity and happiness............to move further .........GO and FLY

Secondly the color signs are Universal and acceptable, even if for those people, who are illiterate. 

Red light weakens the least in travelling in the air. That isWhy stop signs and other critical lights are red. Our retina is covered with light sensitive receptors known as cones (mostly in the centre of retina and responsible for colour sensing) and rods (mostly on the edge of retina andresponsible for perceiving shades, night vision, movement, but notColour). There are three types of cones, each sensitive to one of threecolours of red, blue, or green.

I understand it now:)

you are right  mr.Raafat