Racing the Yellow - A brief history of traffic lights

The first traffic signal, as we would recognize it, was not installed in the United States. In fact, it was placed outside the Parliament building in London, England in 1868. This signal was what is known as a semaphore signal, with arms that read "Stop" and "Go". It was operated by hand by a police officer who was stationed at the intersection.

While this is a newer example of a semaphore traffic signal, it still shows the arms which tell traffic to either stop or proceed.


 The first electric traffic lights in the United States were installed in Salt Lake City, Utah in 1912. These were the first to use the now familiar red and green lights. These signals, however, did not use the modern amber light that we have become accustomed to. These signals contained only red and green lights, forgoing the middle amber.

This is an example of an early traffic light. Instead of containing the three-light system that we are used to today, it uses only red and green.

The yellow light that we are used to was not introduced until much later in traffic signal usage. Even then, amber lights did not have the same meaning as they do today. Proposed meanings for the yellow light included using that color as a cue to clear the intersection, signal for left-hand turns, signal pedestrians to go in all directions, as well as it as used today - as a warning that the light is about to change. Early on, the meanings of the colors of traffic lights were not standardized. Relatively quickly, there was a push to standardize the meanings of the colors, in order to prevent accidents. There were even concerns over the use of yellow lights. It was believed that if drivers knew when the light was going to change, they would try to anticipate the light, which would cause accidents. This is somewhat surprising, as a similar phenomenon occurs at modern intersections with modern lights.


The push to use automatic traffic lights was sparked to free up police officers. Prior to automatic signals, signals had to be operated by a police officer by hand. This caused many intersections to be unattended during an emergency situation. If the lights were controlled automatically, the intersection wouldn't be insecure. Another reason automatic signals became popular over manned intersections were that they were cheaper, per year, than a manned one.

The synchronization of lights was also seen as important very early on. They knew that if timed lights were used, they would eventually slow down traffic unnecessarily. They realized that if the lights were synchronized, a driver could continue down a road unimpeded. This is interesting because the synchronizations of lights is still used, as is seen in downtown Buffalo.