this was very confusing,so in 1924 the city adopted the system used in railroads:red for stop,green for go,and yellow for slow.this system became standard all over the world.
the first automatic traffic lights were installed in wolverhampton, england,in 1927. today computers control traffic lights, and road conditions are much better than they used to be.the only problem is when there is a power outage. the result is often confusion on the streets because the traffic lights don't work.