As early as 1722, the city of London had a system of traffic police to control the flow of vehicles. These officers were given the task of directing traffic in and out of London and Southwark.
Before traffic signals, these officials controlled the movement of vehicles using semaphore arms and red and green lamps. These were designed for night-time travel and were 8 feet tall with a warning sound to alert travelers that a signal was in effect.
In 1868, John Peake Knight filed a patent for a new type of traffic light that would help trains pass safely through an intersection. The signal had three semaphore arms, each equipped with a red and green lamp operated by gas for nighttime use.
Today, traffic lights are used at all types of intersections around the world. They are a major contributor to the safety of motorists, pedestrians, and cyclists.
One of the most important features of these signals is their "mapping." These are programmable visibility devices that only display certain light patterns to specific lanes of traffic. A 12" Fresnel lens, tinted to ITE chromaticity and luminance standards, collimates the output of each light so that it shows up uniformly on the front of the signal for each lane.
Besides the traditional red, yellow, and green lights, modern signals can also be programmed to emit a signal that is intended for deaf and blind people who cannot hear or see the lights. This can help those with limited vision or hearing to know when it is safe to cross.