Red, yellow and green are the colors of traffic lights today, but it wasn’t always like that. The first (and disastrous) attempt to install a traffic light was on December 10, 1868, which is also the official date of installation of the first traffic light in the world. He was in London, in front of the British Parliament, and he worked on gas. It consisted of two movable signs attached to lever-operated arms, and was illuminated at the top to ensure visibility even at night. However, the unfortunate scoreboard did not last long. Less than two months later, it exploded and killed a policeman who was putting up signs.
The world only became ready for traffic lights after electricity became common in cities. Cleveland (America) had the honor of becoming the home of the first two-color traffic light that worked on electricity. Detroit and New York added yellow between red and green in 1920. In Europe, the first traffic light appeared in Paris in 1923, followed by other major cities: Berlin installed traffic lights a year later, followed by Milan, Rome, London, Prague and Barcelona.
The first convention for the unification of road signaling was signed in Geneva in 1931. Its goal was to increase road traffic safety and facilitate international traffic on roads with uniform signaling. Most of the signs we see on the streets today were determined by that agreement, and traffic lights with three colors (red, yellow, green) became standard. The colors of the traffic lights are taken from the railway traffic. At first, the railroad used red to indicate stop, white to indicate movement, and green to indicate caution.
However, white color did not prove to be a good solution as it could be easily confused with the starlight at night. Thus, the color yellow was introduced. When it comes to color perception, red has the longest wavelength, followed by yellow and green. Colors with the longest wavelengths are chosen for signaling because longer wavelengths can travel a greater distance. As a result, red light can travel the greatest distance in rain and fog.
Source: dnevnik.hr