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Invention:	Traffic Light
Function:	noun / trsffic signal / stoplight
Definition:	A road signal for directing vehicular traffic by means of colored lights, typically red for stop, green for go, and yellow for proceed with caution.
Patent:	As a government emplyee Potts could not patent his invention.

Inventor:	William L. Potts
Criteria:	First practical. Modern prototype.

Story:
Even during the horse and buggy days, traffic in big cities was often heavy. Police officers had to be stationed full time directing traffic at busy intersections.
 
The world’s first traffic light came into being before the automobile was in use, and traffic consisted only of pedestrians, buggies, and wagons.  Installed at an intersection in London in 1868, it was a revolving lantern with red and green signals.  Red meant "stop" and green meant "caution."  The lantern, illuminated by gas, was turned by means of a lever at its base so that the appropriate light faced traffic.  On January 2, 1869, this crude traffic light exploded, injuring the policeman who was operating it.

With the coming of automobiles, the situation got even worse. Police Officer William L.  Potts of Detroit, Michigan, decided to do something about the problem.  What he had in mind was figuring out a way to adapt railroad signals for street use.  The railroads were already utilizing automatic controls. But railroad traffic traveled along parallel lines.  Street traffic traveled at right angles. Potts used red, amber, and green railroad lights and about thirty-seven dollars worth of wire and electrical controls to make the world’s first 4-way three color traffic light. It was installed in 1920 on the corner of Woodward and Michigan Avenues in Detroit. Within a year, Detroit had installed a total of fifteen of the new automatic lights.

At about the same time, Garrett Morgan of Cleveland, Ohio realized the need to control the flow of traffic. A gifted inventor and reportedly the first African American to own an automobile in Cleveland, Ohio, he invented the electric automatic traffic light. Though it looked more like the semaphore signals you see at train crossings today.

Many others had obtained US Patents for Traffic Signals, some as early as 1918. But Morgan's Patent was purchased by General Electric Corporation and provided the protection they needed to begin building a monopoly on traffic light manufacture.

Milestones:
1918 U.S.Patent # 1,251,666 issued January 1, to J.B. Hoge of Cleveland, OH
1919 U.S.Patent # 1,307,544 issued June 24,  to Oscar A. Erdmann of Detroit, MI
1920 William Potts invents and installs a three color, four direction taffic light in Detroit, MI
1923 U.S.Patent # 1,475,024 issued November 20, 1923 to Garrett Morgan for traffic signal
ARYs: traffic light, traffic signal, stop light, William Potts, Garrett Morgan, J Hoge, Oscar Erdmann, history, invention, stroy, facts, biography, inventor.