The first traffic light with red and green light was installed in front of the London Parliament in 1868. J. P. Knight , who was an expert in the railway signalling, designed this traffic light as a rather outmoded railway semaphore with two arms and two gas lamps – red and green. A policeman was changing the lights manually and the signalling served mainly for stopping the traffic, to allow the pedestrians to cross the street. But the traffic light was standing on its place for only a year. Then one of the lamps exploded and injured the policeman who was attending it. A modern type of traffic lights was introduced in 1914 in Cleveland in Ohio. It had red and green light and a warning sound signal, which was always set off when the lights were changing. Three-colour traffic lights with red, green and yellow lights were installed in New York in 1918 and were attended by an assistant seated in a box high above the crossroad. The French installed traffic lights in Paris in 1923 and completed them with a gong, which was there to draw the drivers´ attention to the fact, that the lights would be changed. The semaphores came back to London in 1926. All these traffic lights were still attended manually. The first automatic traffic light could be seen in Wolverhampton, England in 1927.

A four-way version of a traffic light from the 40s (Crouse-Hinds)

A four-way  traffic light from the 60s

(all figg from  http://www.geocities.com/CapeCanaveral/Launchpad/1552/signalfan.html)