Who came up with the colors for the traffic lights?

The history of the first traffic light goes back to December 9, 1868, in London. This traffic control tool, which is now essential for managing the amount of cars and pedestrians that move through cities, was inspired by the gas lamps that were already being used on the railways.

Colors of the traffic lights.
Colors of the traffic lights.
⬛ Red and green were already used on the railways because of their intensity and visibility.

John Peake Knight, a British railway engineer, proposed using two gas lamps, one green and one red, so that they could be seen in the dark. In fact, those colors were already used on the railroads because of their intensity and visibility. 

⬛ However, it was a difficult mechanism that, after two months of operation, on January 2, 1869, it exploded and caused the death of the operator in London.

Already in 1910, the engineer Earnest Sirrine made improvements in the traffic light of Peake Knight: he designed an automatic model with the words stop and proceed. 

The green and red automatic lights was a 1912 invention of Lester Wire, a policeman from Salt Lake City, and would be patented by William Ghiglieri and installed in the city of San Francisco five years later. 

The advantage is that the traffic light could be activated or deactivated on purpose by the police, for emergencies. It is worth mentioning that this invention was never patented.

The three lights that currently regulate urban traffic around the world were completed when, in 1914, the American police officer William Potts added the color amber, as a transition stage between movement and stop, in a traffic light in the city of Cleveland.

Finally, in 1936, Charles Marshall devised a rotating traffic light, which showed the seconds remaining before the green signal ended and the red one appeared. However, his invention was not successful: It looked like a clock whose handles ran along the green, red, and briefly the yellow signal.

⬛ It seems that this model was less intuitive and more difficult to understand.

Old traffic light model.
old traffic light model.
⬛ A model of a rotating traffic light (in the image) is preserved in the Melbourne Museum /WikiCommons.

How did the citizens welcome the arrival of the first traffic light?

Documented testimonies testify that the pedestrians, at the beginning, had a lot of difficulties to adapt to this new system of automatic lights. On the other hand, the opposite is not to be expected, as it happens every time a new device is installed among the population. 

It was not until the 1920s that the need for a traffic control system began to be considered, which would state that all road users had the same rights, whether they were on foot or in a car, and that human life was considered to be above the right to travel at a certain speed.

Throughout the 20th century, traffic lights evolved. Gas lamps were eventually replaced by LED lights, which were much more efficient and safe. 

In fact, they consume only 10% of the energy needed by old incandescent lamps. Now, the traffic light is an essential civic element in cities, and one that puts the rights and safety of pedestrians and car drivers on an equal footing.