Puzzle 5 Answer

     The first traffic light was installed in London, England in 1868, long before the invention of cars.  It was used to prevent pedestrians from being trampled by the horses.  The device looked like railway signals.  Semaphore arms were used in the days, but green and red lamps were used at night to represent "caution" and "stop".   A policeman had to turn a lever to change the light.  The first automatic traffic lights like those we are using were installed in the 1920's in Detroit, Michigan, USA.

Source of information: Extraordinary Stories Behind the Invention of Ordinary Things* by Don L. Wulffson

*This book is out of print.  You may look for it in your local library.

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