A Traffic Cop with a manually operated traffic signal, Philadelphia, 1922.
Shortly after the automobile first hit the streets, cars started crashing into each other. Very quickly, it became clear that there needed to be rules and systems in place to make sure people weren’t driving their cars into other cars or people or buildings. Traffic signals were invented to tell motorists when to stop and when to proceed through an intersection. In the days before electric traffic signals, the only option was to have manual signals, like the one shown here, that were changed from ‘stop’ to ‘go’ by a traffic stop operator.
end quote from:
http://historydaily.org/30-rare-historical-photos-and-the-story-behind-them/5
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