More Traffic Light History
London, 1868. This is believed to be the first traffic light ever invented. Built to provide a safe crossing for pedestrians against the heavy flow of horse drawn traffc at the time. It had both a red light and green light, as well as an arm indicator to indicate stop. Police officers would have to change the light manually. (ukroads.org)
The intersection of the first traffic light today. The approach to Westminster Bridge in the background. (Google streets).
The light worked quite well for about a year until disaster struck …. a problem with the gas flow caused an explosion and took out the light as well its accompanying operating officer. Further efforts to revive the light were thwarted by a sudden lack of volunteers to operate it . (photo http://iconicphotos.wordpress.com/2010/02/ )
In 1921 William L Potts, a police officer in Detroit conceived the basic electric traffic light. The lenses and sun visors were small, its design simple, but it is regarded as basis for the first ever self operating electric traffic light.
Based on Potts original traffic light, this is a simple 3 bulb light (model Darcy C811) . You can see it operate here http://www.youtube.com/watch?v=VWcvTErt1YA. Since it only used 3 bulbs, the same bulb lit the red in one direction and green in the other, (and one for yellow for both ways). (http://www.kbrhorse.net/signals/old_sequences.html)
New York City stayed with the two light design for some time. There were still some of these around less than 10 years ago.
Traffic Light Oddity …
Probably the world’s only green on top traffic light. Located in a heavily Irish suburb of Syracuse, the towns Irish population refused to allow green to be in any other place than on top of the signal.