Who invented the traffic light?
TRAFFIC lights were first used before the cars we most associate them with today even existed.
Signalling lights were used on railways during the 19th century - but the first patent for the three-light traffic light system was not given until the 1920s. So who came up with it?
Who invented the traffic light?
Nottingham railway engineer J P Knight invented a traffic light which was used in London outside the Houses of Parliament on December 10, 1868.
While motor cars did not hit the streets of the UK until later in the 19th century, Knight’s system was put in place to regulate horse-drawn carriages.
Red and green signalling arms were operated by a policeman during the day, and gas-lit lanterns were used at night.
But only a month after Knight’s lights were installed, a policeman was killed when a lamp exploded, in early 1869.
The next British traffic lights were not seen until 1925, at the junction of St James’ Street and Piccadilly. These were also manually operated by a policeman.
Meanwhile, in the USA, American policeman Lester Wire designed the first two-colour, red/green electric traffic light system, in 1912.
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It was installed in Salt Lake City in Utah on August 5, 1914.
Six connected intersections were controlled simultaneously in the first interconnected traffic signalling system, also in Salt Lake City, in 1917.
But it was James Hoge who was given the patent for his own system which was installed in Cleveland, Ohio, in 1917.
His traffic system used the illuminated words "Stop" and "Move" alternately, on each of the four corners of an intersection, to control the flow of traffic.
William Potts, a police officer from Detroit, invented the first three-colour traffic light, also in 1917, followed by the four-way light in 1920.
The first three-colour system was used in New York in 1918.
Potts’ four-way signal, with an electric light, was installed on the corner of Woodward and Michigan Avenues, Detroit, in 1920.
Meanwhile, Garrett Morgan, a sewing machine repairman and hair-care product designer from Ohio, was granted the patent for his three-light electric automatic system on November 20, 1923.
The system was installed in Cleveland, Ohio, and Morgan also invented a firehood, which was a forerunner to the gas mask.
In 1928, American engineer Charles Adler Jr invented the first sonically-activated traffic light, which was installed in Baltimore, Maryland, in the same year.
Adler's system involved drivers pulling up to a red light and honking their horn to activate it.
Adler also invented the pedestrian push button in 1929, which was installed in Baltimore.
Computerised traffic detection systems emerged in the 1950s, and computer monitoring and automatic adjustment became possible in the 1960s.
The pedestrian countdown timer was introduced in the 1990s, and by 2010, connected vehicles could connect via a wireless network to traffic lights.
Future conversations have included the possibility of adding a blue light, to mean follow the car in front.
Why was the traffic light invented?
Traffic signalling systems were introduced to avoid collisions and ease congestion, and lights were used because they were more effective than coloured objects in previous systems.
The traffic lights introduced to London in 1868 were installed to control the congestion of horse-drawn vehicles.
William Potts designed his traffic lights because he realised the streets were becoming so busy with cars.
His main concern was intersections where four-lane road traffic crossed railways at right angles.
And Garrett Morgan was inspired to design his traffic light system after he was left distressed when he witnessed a crash between a car and a horse-drawn carriage.
Decades before, traffic signalling was introduced on the first railways, where trains going in both directions shared a single track.
They used a system with a ball and a kite - the ball was in the air if it was safe to go, and the kite signalled stop.
Coloured oil lamps, red for stop and white for go, were used on railway signal arms at night as early as the 1840s.
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After a massive train crash in 1876, the yellow light was added to indicate "proceed with caution".
And in 1893 green lights replaced the white light, as lights from housing and streets made it difficult for drivers to see the white.