Who Invented the Traffic Signal?

Early Traffic Signals


Traffic lights had been in use even before cars were invented. In those days, people used horses, wagons and other means of transport. But the traffic was still horrible. So in 1868 in London, England, traffic enforcers came up with a basic device: A lantern with two lights – red and green. Green stood for “caution” and red for “stop.” A policeman would turn the lights regularly with a lever. Unfortunately this early traffic light proved unsafe. One model exploded a year later and hurt the operator.

Automobiles and the Invention of the Modern Traffic Signals

Things made a turn for the worse when cars were invented. In the early 20th century, transportation was in transition. Some people were using the new automobiles, others were still riding horses, wagons or bicycles. They all shared the same roads and streets with pedestrians. A lot of accidents took place as a result.


A traffic police officer named William L. Potts, from Detroit, Michigan knew something had to be done. He saw as automated railroad signals as a model for street traffic signals. But the difference was railroads went on a straight path; streets were at right angles. So Potts designed a traffic signal device that could service four-way streets. He used three colors red, yellow (or amber) and green. He put the signal together with electric controls and wires. In 1920, he had it installed on the Michigan Avenue – Woodward corner street. These were the first automatic traffic signals. Detroit police went on to add fourteen more of these in twelve months.

Patent for the Invention of the Traffic Signal

As useful as Police Officer Potts’ invention was, he was not the first nor the last to have thought of making a traffic signal. Other men had applied for patents to similar designs before. These were J.B. Hoge of Cleveland, Ohio in 1918; and Oscar A. Erdsman also of Detroit, Michigan in 1919.

Then came 1923, three years after Potts’ team installed their first traffic signals in Detroit streets. Garrett Morgan of Cleveland, Ohio applied and got a patent for his own traffic signal. Morgan had invented the gas mask in 1916. Now he designed a traffic signal that was a t-shaped rod with three actions: stop, go and “all stop” for all directions. The last one was for pedestrians to cross safely. This, too, was manually operated. Morgan sold the rights to his invention to General Electric Corporation for $40,000.