1914 is a reasonable guess. In the United States, cars were becoming popular, so traffic was increasing. In 1900 there were about 8,000 motor vehicles on the road. By 1910, there were 460,000 cars and trucks, and by 1920 more than 8 million.
But 1914 isn’t right. It was 1868. In London, England.
In 1868, London had lots of horse-drawn traffic (motorized vehicles were still in the future). There was so much traffic that a traffic signal called a semaphore was installed at the intersection of George Street and Bridge Street near the Houses of Parliament. The purpose was to provide a safe crossing for pedestrians, especially members of Parliament.
A semaphore is a tall post with moveable arms. The one at right is similar to the one installed in London in 1868. The arms sticking straight out sideways meant stop. At night a gas light at the top was lit. The light had a red lens for stop and a green lens for go.
Traffic police and early signals
Traffic police officers operated semaphores and early traffic lights by hand. City officials didn’t think drivers would obey the signals if traffic officers weren’t there to enforce them. The traffic officers judged the traffic and decided when to change the signal. To alert traffic that the signal was about to change, they blew a whistle.
Besides cars and trucks, traffic included street cars (vehicles traveling on rails) and horse-drawn vehicles. With all this traffic, one problem that officers had was being able to see and be seen by drivers, especially at congested intersections.
To give traffic officers a wider view, many cities in the United States started using traffic towers in the late 1910s and 1920s. These towers were small booths several feet above street level. Some towers were on street corners. Some were on concrete islands in the middle of a street or intersection. The officers inside the towers operated colored lights or semaphores or waved their arms.
The tower design in the top photo at right was used in Detroit, Michigan, in the 1920s. A traffic officer controlled signal lights at the top of the tower and at driver eye level.
Detroit was a hotbed of innovation for traffic signals. In 1917, Detroit installed the first traffic tower in the United States at the intersection of Woodward Avenue and Michigan Avenue. In 1920, Detroit became the first city to use red, green, and yellow lights to control traffic. And a Detroit police officer named William L. Potts invented the 4-way, 3-color traffic signal.
During the 1920s inventors came up with plenty of different designs for traffic signals.
One thing these signals usually had in common was that someone had to push a button or flip a switch to change the signal. Imagine the thousands of police officers whose job it was to operate signals and enforce traffic laws at intersections. Once automated signals were invented, traffic officers were freed up for other duties.
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