June 13, 2018

Traffic Lights: A Short History

Posted By: Paul-Matthew Zamsky, Head of Strategic Partnerships at Waycare

Who invented traffic lights? 

The red-orange-green lights, so familiar on city streets, were preceded by police and traffic officers using hand signals.  

The first set of traffic lights were gas-lit and installed in London, outside the Houses of Parliament, on December 9, 1868, almost 150 years ago. The inventor was a railway engineer, J. P. Knight, who got the idea from his railway signal system. The system used three semaphore arms (a system of signaling, using flags or poles)  with red and green (no orange) gas lamps for night-time use on a pillar operated by a police constable. The system was short-lived and ended tragically when it exploded on 2 January 1869 as a result of a gas leak hurting the police officer operating it. [1] 

From 1900 through 1920,  semaphore traffic signals operated by police were used all over the U.S.  Each state had its own design but generally, they were white “stop” and “go” signs on a green background. At night, the system relied on kerosene lamps and a combination of red and green lenses. 

The modern electric version of traffic lights emerged in 1912 when a Salt Lake City Utah police officer developed red and green electric stoplights and in 1914 a similar system was installed in Cleveland.

In 1920, the first four-way three-color traffic light was invented in Detroit by another police officer, William Potts. A couple of years later automatic timers were introduced, and the traffic-light innovation spread quickly throughout the US in tandem with as the commercialization of the Model T Ford, the first middle-class accessible car.

The control of traffic lights leaped ahead when computers were put to use in the 1950s and the 1960s, a pressure plate was placed at intersections so that once a car was on the plate computers would know that a vehicle was waiting at the red light. An example of this computerized control of lights was developed in Denver as early as 1952.   One computer took control of 120 lights with six pressure-sensitive detectors measuring inbound and outbound traffic.

Today the city of Amsterdam has a sophisticated system of sensors, pressure plates and computer-controlled traffic lights, that change from red to green and back only when traffic flows warrant it. However today most traffic lights still remain controlled by a 30-second timer, despite this technology being prototyped as early as 1952.

Why have we not adopted such technology over the years? Traffic flow could be improved immensely.  

The answer is probably cost. The cost of poorly timed traffic lights is a hidden cost that currently falls on the driver. The driver’s time doesn’t translate to a specific line item, but if it were, perhaps we would see more ‘smart cities’ with ‘smart traffic lights’ that knew when to turn red based on traffic, rather than based on a clock or timer.

[1]  BBC. “The man who gave us traffic lights”.   September 2016.

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