Even if the road signs are as old as the roads (the Romans had already erected stone column markers along them to indicate the distances to Rome), the establishment of a real signaling system does not begin until the end of the 19th century. That is almost a century after the invention of the first “automobile” vehicle (which “moves by itself”) by the Frenchman Joseph Cugnot, in 1771.
From the gas lantern ...
As drivers do not all know how to read or do not read the language of the country they are crossing, it is necessary to put in place signage without text, made up of pictograms and colors. The very first red light was erected in London on December 10, 1868. It was in fact a gas lantern mounted on a steel foot 7 meters high. On the one hand, it is red to say "stop", on the other it is green for "attention". It is turned with a lever. For the anecdote, the agent in charge of its operation was seriously injured when it exploded fifteen days later.
... at the traffic lights
But it was in 1914, in Cleveland, United States, that the first electric red light was installed. It is visible from a distance and from any point of the intersection that it regulates, and functions rather summarily: in red we stop, at the bell we start. It was Garrett Augustus Morgan, a sort of “Geo Trouvetout” and inventor, among other things, of the gas mask that saved so many lives during the Great War, who developed it. He also sold his patent to the General Electric Company for 40,000 dollars at the time. On May 5, 1923, this electric red light was installed in Paris at the crossroads of Saint-Denis and Sébastopol boulevards, before the green and orange lights - the traffic light that we know - appeared. It has since been one of the major elements in the regulation of automobile, rail and river traffic.