In 1912, Lester Wire of Salt Lake City, Utah invented an electric traffic light that used red and green lights. However, he did not apply for a patent. The next year, James Hoge received patent no 1,251,666 for a manually controlled traffic light system using electric lights. It was installed in Cleveland, Ohio in 1914, displaying the words STOP and MOVE.
The first traffic light system to use red and green lights were patented by William Ghiglieri of San Francisco, California in 1917 (patented no 1,224,632). His design could be operated manually or in automatic.
The amber light was added in 1920 by William Potts, a Detroit policeman. He actually invented several traffic light systems, including the overhang four-way system, but did not apply for patents. The first person to apply for a patent to produce inexpensive traffic lights was Garrett Morgan, who received his patent in 1923
Automatic control of interconnected traffic lights was introduced March 1922 in
Houston, Texas.
Ashville, Ohio claims to be the location of the oldest working traffic light in the United States, used at an intersection of public roads until 1982 when it was moved to a local museum.
The first interconnected traffic signal system was installed in
Salt Lake City in 1917,[
citation needed] with six connected intersections controlled simultaneously from a manual switch.