Before traffic lights, traffic police controlled the flow of traffic. A well-documented example is that on London Bridge in 1722.^:3 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.

On 9 December 1868, the first non-electric gas-lit traffic lights were installed outside the Houses of Parliament in London to control the traffic in Bridge Street, Great George Street, and Parliament Street. They were proposed by the railway engineer J. P. Knight of Nottingham who had adapted this idea from his design of railway signalling systems and constructed by the railway signal engineers of Saxby & Farmer. 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 Houses of Parliament. The design combined three semaphore arms with red and green gas lamps for night-time use, on a pillar, operated by a police constable. The gas lantern was manually turned by a traffic police officer with a lever at its base so that the appropriate light faced traffic. The signal was 22 feet (6.7 m) high. 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".

Although it was said to be successful at controlling traffic, its operational life was brief. It exploded on 2 January 1869 as a result of a leak in one of the gas lines underneath the pavement and injured the policeman who was operating it.

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 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 were 8 feet (2.4 m) above ground.^:22 It was 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.^:23 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.

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.^:33

An electric traffic light was developed in 1912 by Lester Wire, a policeman in Salt Lake City, Utah, who also used red-green lights. On 5 August 1914, the American Traffic Signal Company installed a traffic signal system on the corner of East 105th Street and Euclid Avenue in Cleveland, Ohio.^:27–28 It had two colours, red and green, and a buzzer, based on the design of James Hoge, to provide a warning for colour changes. The design by James Hoge allowed police and fire stations to control the signals in case of emergency. The first four-way, three-colour traffic light was created by police officer William Potts in Detroit, Michigan in 1920. Ashville, Ohio claims to be the home of the oldest working traffic light in the United States, used at an intersection of public roads from 1932 to 1982 when it was moved to a local museum. Many pictures of historical traffic lights appear at a Traffic Signal Trivia page.

The tower was the first innovation that used the three-coloured traffic signal and appeared first in the City of Detroit, where the first three-coloured traffic light was built at the intersection of Michigan and Woodward Avenues in 1920. The man behind this three-colour 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 coloured amber, which was the same colour used on the railroad.^:93 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 the world, with over 20,000 vehicles daily.^:35

Los Angeles installed its first automated traffic signals in October 1920 at five locations on Broadway. These early signals, manufactured by the Acme Traffic Signal Co., paired "Stop" and "Go" semaphore arms with small red and green lights. Bells played the role of today's amber or yellow lights, ringing when the flags changed—a process that took five seconds. By 1923 the city had installed 31 Acme traffic control devices. The Acme semaphore traffic lights were often used in Warner Bros. Looney Tunes and Merrie Melodies cartoons for comedic effect due to their loud bell.

The first interconnected traffic signal system was installed in Salt Lake City in 1917, with six connected intersections controlled simultaneously from a manual switch.^:32 Automatic control of interconnected traffic lights was introduced March 1922 in Houston, Texas.

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.^:385 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.^:385

After witnessing an accident between an automobile and a horse-drawn carriage, African American inventor, Garrett Morgan, filed a U.S. patent for a traffic signal. Patent No. 1,475,024 was granted on 20 November 1923 for Morgan's three-position traffic signal.

The first traffic lights in Britain were deployed in Piccadilly Circus in 1926. Wolverhampton was the first British town to introduce automated traffic lights in 1927 in Princes Square at the junction of Lichfield Street and Princess Street.

Melbourne was the first city in Australia to install traffic lights in 1928 on the intersection of Collins and Swanston Street.

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 sand-blasted to increase daytime visibility.^:383

Both the tower and semaphores were phased out by 1930. Towers were too big and obstructed traffic; semaphores were too small and drivers could not see them at night.^:382

The first traffic light in South India was installed at Egmore Junction, Chennai in 1953. The city of Bangalore installed its first traffic light at Corporation Circle in 1963.

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 Crosby's 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.^:135 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.^:141 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