Next time you are sitting at a traffic light you will know much more about them. Read the whole article at mental_floss.
Long before the invention of the internal combustion engine, horses and people were already having so much trouble yielding to each other at intersections that, in 1868, a British railroad engineer designed the first traffic signal to help them out. Oddly, the contraption only featured two settings: “stop” and “caution,” indicated by a bar held horizontally or lowered to a 45-degree angle. At night, red and green lights were used to make the bar visible, meaning that, in this case, “green” meant “slow down.” A proclamation issued by London’s police commissioner in 1868 explained the system as well as the then-novel concept of pedestrian right-of-way, and for the first time, cities had a way to keep people from constantly running into each other.