Who invented traffic lights?

It was a man from Nottingham who created the first road traffic management system. 

Engineer John Peake Knight was a railway manager. He specialised in developing signalling systems for Britain’s growing railway network. During the early 1860s there was growing concern about the amount of horse-drawn traffic on the streets of London, which was becoming increasingly dangerous for pedestrians crossing the roads. It was clear that a traffic management solution was needed. 

Knight proposed adapting the gas lamp system used in signalling on the railway for traffic management on roads. He approached the Metropolitan police and suggested using a semaphore/lighting system to control road traffic. The semaphore system would have an ‘arm’ or arms that could be raised and lowered by police to indicate the flow and stop of traffic during daylight hours, along with a green (for go) and a red (for stop) gas lamp - for use at night. These two colours were suggested because they could be clearly seen in the dark and were already being successfully used on the railway. 

It took three years for Knight’s suggestions to be implemented but on 9 December 1868, the system was put in place at the junction of Great George and Bridge Street in London, near the Houses of Parliament. The traffic system initially worked well. Unfortunately after just over a month, one of the gas lines that supplied the lights began to leak. A policeman who was operating the system at the time was unaware of the leak and was severely burned when one of the lamps exploded. This system was immediately withdrawn from use. 

By 1910 an American engineer, Ernest Sirrine, made some significant improvements to Knight’s preliminary traffic light system. Sirrine designed an automatically controlled traffic signal in Chicago. His system used two non-illuminated display arms arranged as a cross that rotated on an axis, according to Inventor Spot. The signs said "stop" and "proceed."

The first electric traffic light using red and green lights was invented in 1912 by Lester Farnsworth Wire, a police officer in Salt Lake City, Utah. Wire's traffic signal looked similar to a four-sided bird-box mounted on a tall pole. It was placed in the middle of an intersection and was powered by overhead trolley wires. A police officer was required to manually switch the direction of the lights. 

The three light system that currently regulates traffic around the world was first introduced in 1914, when the American police officer William Potts added the colour amber, as a transition stage between movement and stop, in a traffic light in the city of Cleveland.

The first electric traffic light in Europe was installed in 1924 at Potsdamer Platz in Berlin, according to Marcus Welz, CEO of Siemens ITS (Intelligent Traffic Systems) USA. The five-sided traffic light was mounted on a tower and was primarily manual with some automation. This system only required one police officer to manage it. 

In 1936, the Australian inventor Charles Marshall created the first rotating traffic light, known as the Marshalite. This system looked like a clock, but was ultimately a failure. It seems that this model was confusing and difficult to interpret. 

Pedestrian signals began to be included on traffic signals in the 1930s, according to the US Department of Transportation. A "Walk/Don't Walk" signal was first tested in New York in 1934.

As the 20th century progressed, as did traffic light technology. Gas lamps were replaced by LED lights, which provide a safer and more energy efficient system of traffic control. Traffic signals continue to improve. Many traffic signals are now classified as 'intelligent' and can monitor real-time traffic situations, including direction, volume and density, as well as prioritising public transportation systems.