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The History of Traffic Light Sizes

Traffic Light Sizes

The traffic light is one of the most commonly used devices to regulate the flow of traffic. It is estimated that there are more than three hundred thousand traffic lights in the United States alone.

The size of the traffic light has gone through many changes since its inception over one hundred years ago. Here is a brief history of how traffic light sizes have changed over time.

The Original Traffic Lights

The first Traffic lights were invented by J.P. Knight in 1868. His original design had two semaphore arms and two red lamps. The arms were symmetrical and both were the same size.

The red lamps were also the same size, but the upper lamp was larger than the lower lamp. This was done so that the light would be visible from a greater distance. The arms and lamps were mounted on a post that was approximately eight feet tall.

The Modern traffic Light

In 1923, Garrett Morgan patented the modern traffic light. His design had a T-shaped pole with three color-coded aspect lenses facing in each direction, arranged so that only one lens was lit at any time to indicate to drivers whether they could proceed (green), should prepare to stop (yellow), or must stop (red).

The advantage of Morgan’s design over Knight’s was that it was easier for police officers to control and more reliable due to its use of incandescent bulbs instead of gas lanterns.

However, his design did not catch on immediately, and it wasn’t until 1930 that Detroit became the first city in the United States to replace its manually operated semaphore traffic signals with electric-powered stoplights according to Morgan’s design.

Traffic Light Sizes Today

Nowadays, most traffic lights are between four and six feet tall. They generally have three aspects (red, yellow, and green) although some also have a fourth aspect (arrow) to indicate when turns are permitted.

The size of the traffic light varies depending on several factors such as the speed limit of the road, the average number of vehicles on the road, and the visibility conditions (e.g., whether there are trees or buildings blocking visibility).

In general, though, most traffic lights are between four and six feet tall.


Today, almost all traffic lights are between four and six feet tall and have three aspects (red, yellow, green).

However, this has not always been the case. The size of traffic lights has changed throughout history due to various factors such as visibility conditions and police officer preference.

The next time you’re stopped at a red light, take a moment to appreciate how far these devices have come!