The first 3-colored traffic signal

[tradephoric]

How would you like this traffic signal for the man cave?  It is supposedly the first 3-colored traffic signal in the nation and is on display at the Henry Ford Museum.  Detroit traffic officer William Potts created this three-color, four-way traffic signal in 1920. Previous illuminated signals used only red and green lights. The addition of an amber "caution" light made driving safer and the three-color signal became the standard by the mid-1930s. This first traffic light was installed at Woodward Avenue and Fort Street in Detroit, Michigan.



Because the four lenses in each compartment of Potts' signal were lit by a single bulb, two sides of the signal facing the main road had to be provided with red on the top section and green on the bottom while the cross street had to have green on the top and red on the bottom. Since at the time there were no standards as to where different colors were located, the positions of the red and green lenses were not confusing to motorists.

[M3019C LPS20]

I know a signal collector outside of this club that made a replica of the Potts signal, and he currently displays it in his collection.

As a correction, the uniform three-color system for traffic signals came about in 1925. While it is true many municipalities adopted the amber indication, some cities declined, like New York City. Interestingly enough, in the 1920s decade, the city had the amber signal in use for archaic traffic towers at busy intersections, but the meaning was entirely different than what we know of it today. Then, amber meant northbound and southbound traffic had the right-of-way, while eastbound and westbound traffic waited. The green signal was the total opposite of amber's original meaning.

[roadman]

Various toy battery-powered traffic lights made in the 1960s, the Buddy-L "Auto Action" traffic light being the best known of them, used the 'one bulb' per indication principle of the Potts signal.  RYG facing one direction, GYR facing the other.

[M3019C LPS20]

Two traffic signal manufacturers, W.S. Darley and Harrington Seaberg, implemented the same configuration in the production of traffic signals in the early 20th century.

Probably an economical way at the time than to use 12 lamps (assuming one traffic signal was four directions).