The first question is why is the red color for stopping while green is for a clear line? Initially, red was embraced by ships as a symbol of danger. Ships had red flags placed at the top to signal other ships not to come closer. At the beginning of the 19th century, Britain started the system of signaling in the railways. The train used to run on a single track; therefore, it was essential to have a system to avoid unnecessary trouble. The red color was accepted as a symbol of danger by that time.
Because green color was picked as the color of a clear line, it was placed at the top. There was another thought linked with it that the height of the signal will be good enough, red will also be seen.
Otherwise also, the signal in that era used to go down and up. They would have a colored plate of glass and lanterns used to be kept behind them at night. The colored plate of glass used to flitter during the day. On 10th December 1868, a railway engineer named JP Night placed a traffic light in front of the British Parliament so that the traffic can be managed well.
This signal was exactly the same as it was there in railway but this system did not work out. The systematic traffic signal on the roads came into the existence in the year 1912 in the Salt Lake City Utah in America. While setting the traffic signals, it was thought that the signals will not be very high, and thus, we better keep the red at the top. Later, it was found in various researches that the color, which draws the attention most is not red, it’s either yellow or saffron with some reddish tinge.
This color was also included in the traffic signals. Most of the signals in the world at the moment have yellow. The color of the life jackets used in ships is also yellow. The flare pistols, which indicate danger also dish out yellow-orange smoke.