Traffic signals invented
Traffic signals were invented in response to the rise of automobile traffic in urban areas during the 1920s, necessitating a system to enhance safety and improve traffic flow at busy intersections. Before their invention, traffic management relied on police officers using manual signals, which often led to accidents due to a lack of sufficient warning. The first mechanized traffic signal was patented by African American inventor Garrett Morgan in 1923, introducing a system that allowed for an all-directional stop to improve pedestrian safety. Meanwhile, William L. Potts developed the first four-sided traffic signal in Detroit in 1920, which laid the groundwork for automated systems. By 1928, traffic signals had evolved to include timers and sensors, leading to the fully automated systems we see today. The standard colors of red, amber, and green, initiated by Potts, have been in use since 1935, with enhancements made for visibility and safety. Overall, the invention of traffic signals marked a significant advancement in urban traffic management, responding to the complexities of mixed transportation modes on city streets.
Traffic signals invented
The invention of the traffic signal was prompted by the increase in automobile traffic in cities during the 1920s. With pedestrians, horse-drawn carriages, and automobiles often sharing the same roadways, the new technology enhanced safety and improved traffic flow while reducing congestion at busy city intersections.
From the late 1800s to the early 1900s, traffic was regulated by police officers who would manually rotate a semaphore to indicate either “stop” or “go.” Because there was little warning given to motorists, collisions and accidents were common, and police officers were often injured.
By the early 1920s, automobiles began to outnumber horse-drawn wagons in many urban areas, and with this increase came an even greater increase in traffic accidents. Traffic towers were used to help regulate congested intersections, and although the police officers were safer in the towers, colored lights or flags were still operated manually, and collisions and injuries at busy intersections continued to be a problem.
African American inventor Garrett Morgan was the first to receive a patent for a mechanized traffic signal. Granted in 1923, the patent called for flags to rotate on a three-position traffic pole. The third position on the pole allowed for an all-directional stop, which meant traffic could be halted in all directions and pedestrians could cross more safely through intersections.
William L. Potts, a police officer from Detroit, Michigan, is credited with developing the first four-sided traffic signal, which was installed at a busy Detroit intersection in October of 1920. The manually operated signal was constructed from wood with a metal shell and had lights made from four-inch green, amber, and red lenses. Within a year, the city had installed the first automated light system, which Potts also designed, that accommodated traffic signals at fifteen separate intersections to be controlled from one location. Some of the signals were installed on top of manned traffic towers; others were suspended over intersections, much like modern traffic lights.
Impact
Late in the decade, traffic signals became fully automated. Until that time, signals required someone to flip a switch, pull a lever, or push a button. By 1928, however, traffic signal design had progressed to include timers or sound and pressure sensors that regulated the timing of the lights. Modern traffic signals, though fully automated, still employ the original red, amber, and green colors introduced by William Potts, and although these three colors have been standardized in the United States since 1935, the size of the lenses has increased two to three times their original diameter, making them more visible at night and in most weather conditions
Bibliography
Barnett, LeRoy. “Michigan Gives the Green Light to Traffic Safety.” Michigan History Magazine 86, no. 4 (July–August, 2002): 22–25.
Challoner, Jack, ed. 1001 Inventions that Changed the World. Hauppauge, N.Y.: Barron’s, 2009.
Packer, Jeremy. Mobility Without Mayhem: Safety, Cars, and Citizenship. Durham, N.C.: Duke University Press, 2008.