History of traffic light

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Picture of a traffic light in the US state of Maryland

The History of Traffic Lights.


A traffic light is a device that is designed to control the flow of traffic by using three colored lights. These lights are mainly green, yellow, and red. In 1860s London, the first traffic control device had arms that extended out to command drivers on how to react at an intersection .[1] The first four way three color traffic light did not come until December 1920 in Detroit .[2]

The first methods used for traffic control[edit]

The true origins of traffic control are unknown to us but historical evidence has proven that traffic problems started when highways came into existence. Man has always had problems with streets filled to the breaking point with travelers. Some of the first strategies for traffic control were not a device but regulations made by governments. One of the earliest examples was in Rome. During the days of Julius Caesar the streets of Rome were so clogged with chariots the government made certain areas off limits to all vehicles except those belonging to people who were public officials and high-ranking citizens.[3] The best historical example of traffic control that relates towards a traffic light is the use of traffic cops to control the flow of traffic on London Bridge in 1722.[4] Three men were given the task of directing traffic coming in and out of either London or Southwark. Each officer would help direct traffic coming out of Southwark into London and he made sure all traffic stayed on the west end of the bridge. A second officer would direct traffic on the east end of the bridge to control the flow of people leaving London and going into Southwark.[5] The first traffic control device that was not human nor an act of regulation appeared in 1868 in London outside the House of Parliament.[6]


The traffic control devices in late 1860s to early 1900s[edit]

The first traffic control device appeared near the British House of Parliament at the intersection of George and Bridge Streets. The device was made in response to the desire by a Select Committee to use railway signals on highways. The device had lights and it used arms which extended outwards. It was operated manually by a police officer. The signal was 22 feet high and crowned with a gas light. The light was called the semaphore and had arms that would extend horizontally that commanded drivers to "Stop" and then the arms would lower to a 45 degrees angle to tell drivers to proceed with "Caution". At night a red light would command "Stop" and a green light would mean use "Caution".[7] The man behind this new and different invention was John Peake Knight a railroad engineer. The main reason for the traffic light was that there was an overflow of horse-drawn traffic over Westminster Bridge which forced thousands of pedestrians to walk next to the house of Parliament.[8] But Knight’s invention was not to last long. After only a month of use the device exploded and injured the police officer who was operating the light. In the first two decades of the 20th century semaphore traffic signals, like the one in London, were in use all over the United States with each state having its own design of the device. One good example was from Toledo, Ohio in 1908. The words “Stop” and “Go” were in white on a green background and the lights had red and green lenses illuminated by kerosene lamps for night travelers and the arms where eight feet above ground.[9] Controlled by a traffic officer who would blow a whistle before changing the commands on this signal to help alert travelers of the change, the design was also used in Philadelphia and Detroit.[10] The example in Ohio was the first time America tried to use a more visible form of traffic control that evolved the use of semaphore. The device that was used in Ohio was designed based on the use of railroad signals.[11]

The first three-colored signal and the traffic tower[edit]

In 1912 a traffic control device was placed on top a tower in Paris at the Rue Montmartre and Grande Boulevard. This tower signal was manned by a police woman and she operated a revolving four-sided metal box on top of a glass showcase where the word “Stop” was painted in red and the word “Go” painted in white. The traffic tower was featured in The Rider and Driver Magazine and soon the United States started to develop their own traffic control towers.[12] The tower was the first innovation that used the three-colored traffic signal and appeared first in the City of Detroit, where the first three-colored traffic light was built at the intersection of Michigan and Woodward Avenues in 1920. The man behind this three-color traffic light was police officer William Potts of Detroit. He was concerned about how police officers at four different lights signals could not change their lights all at the same time. The answer was a third light that was colored amber, which was the same color used on the railroad.[13] Potts also placed a timer with the light to help coordinate a four-way set of lights in the city. The traffic tower soon used twelve floodlights to control traffic and the reason for a tower in the first place was that at the time the intersection was one of the busiest in world, with over 20,000 vehicles daily.[14] The twelve-light system did not become available until 1928 and another feature of the light system was that hoods were placed over the light and each lens was sun-blasted to increase daytime visibility.[15] The popularity of the traffic tower, like the semaphore in the past decade, caught on in other states. Once again different states released their own design for the new traffic tower, and it was popular in places like New York and Detroit. In 1922 traffic towers were beginning to be controlled by automatic timers. The first company to add timers in traffic lights was Crouse Hinds. They built railroad signals and were the first company to place timers in traffic lights in Houston, which was their home city.[16] The main advantage for the use of the timer was that it saved cities money by replacing traffic officers. The city of New York was able to reassign all but 500 of its 6,000 officers working on the traffic squad; this saved the city $12,500,000.[17] The use of both the tower and the semaphores were done by 1930. The tower was great with starting innovation but they were too big and obstructed traffic and the semaphores were too small and drivers could not see them at night.[18]

Traffic light controlled by computer[edit]

The traffic light underwent many evolutions from a manually operated arm extending outwards in 1860s London to being controlled by a timer in a tower at an intersection. The control of traffic lights made a big turn with the rise of computers in America in the 1950s. Thanks to computers, the changing of lights made traffic flow even quicker thanks to computerized detection. A pressure plate was placed at intersections so once a car was on the plate computers would know that a car was waiting at the red light.[19] Some of this detection included knowing the number of waiting cars against the red light and the length of time waited by the first vehicle at the red.[20] One of the best historical examples of computerized control of lights was in Denver in 1952. One computer took control of 120 lights with six pressure-sensitive detectors measuring inbound and outbound traffic. The system was in place at the central business district, where the most traffic was between the downtown area and the north and northeastern parts of the city. The control room that housed the computer in charge of the system was in the basement of the City and County Building.[21] As computers started to evolve, traffic light control also improved and became easier. In 1967 the cities of Toronto and Ontario were the first to use more advanced computers that were better at vehicle detection.[22] Thanks to the new and better computers traffic flow moved even quicker than with the use of the tower. The computers maintained control over 159 signals in the cities through telephone lines. People praised the computers for their detection abilities. Thanks to detection computers could change the length of the green light based on the volume of waiting cars.[23] The rise of computers is the model of traffic control which is now used in the 21st century.


  1. ^ Sessions, Gordon M. Traffic Devices: Historical Aspects Thereof. Washington: Institute of Traffic Engineers, 1971. Page 8
  2. ^ Sessions, 43
  3. ^ Sessions,2
  4. ^ Sessions,3
  5. ^ Sessions, 3
  6. ^ Sessions,5
  7. ^ Sessions,8
  8. ^ Pollard, JustinTHE ECCENTRIC ENGINEER: The history of traffic lights is full of twists and turns". 2008. ENGINEERING AND TECHNOLOGY -IET-. 3 (15): 93. Page 93
  9. ^ Sessions,22
  10. ^ Sessions, 23
  11. ^ McShane, C. 1999. "The Origins and Globalization of Traffic Control Signals". JOURNAL OF URBAN HISTORY. 25 (3): 379-404. Page 382
  12. ^ Sessions,33
  13. ^ Pollard,93
  14. ^ Sessions,35
  15. ^ McShane, 383
  16. ^ Mcshane, 385
  17. ^ McShane, 385
  18. ^ McShane, 382
  19. ^ Sessions, 135
  20. ^ Sessions, 141
  21. ^ Sessions,141
  22. ^ Sessions,141
  23. ^ Sessions, 143