June 28, 2021

Traffic Lights: Did You Know …..?



Post by: Paul-Matthew Zamsky

Consider the traffic light, an ever-present piece of machinery that seemingly keeps our intersections safe. Why are there three colors vertically aligned? Who made these decisions? Today we share some tidbits of knowledge that we hope will make you look at traffic lights a little differently. 

Image Sourced from the Londonist

Traffic Lights: A History 

Where it all began:

At the start, traffic lights were dangerous – but not in the way you may think. The first traffic lights, installed outside the British Houses of Parliament on December 9, 1868, were gas-lit, adapted from railway signalling systems. They were a semaphore system, towers with movable arms that said Stop! (red light) and Caution! (green light). 

Their life was short. In January 1869 one of the gas lines underneath the pavement sprang a leak – and the resulting explosion fatally injured the policeman operating it. The system was then removed.

Why does the color red mean ‘stop’?   

Red light has the longest wavelength of any color in the visible spectrum, which means in general it can be seen from a greater distance than other colors. Red has meant “stop” long before traffic lights existed, dating back to red train signals. And yellow? Well, it’s second only to red in terms of visible wavelength – which is why school zones, school buses and crosswalks are often yellow.

Running the Red: 

Do you ever run a red light? More people than you may think do. One study showed that more than half – 56% of all drivers — admit to running red lights part of the time.  Most of the time – drivers run a light that has just barely turned red, or step on the gas and are in the intersection when it turns red, or when they try to “beat the amber”. This is probably a major irrational miscalculation of risk-reward – but our lives are full of those. In 2015, in the US, 60 people died each month from crashes involving running a red light, and an estimated 200,000 persons are injured each year in accidents involving red-light running. So this problem is no joke – it has serious consequences. 

Why the color yellow? 

In the early days of driving in the US, many conventional ‘stop’ signs (not traffic lights) were actually yellow. Why? Traditionally red signifies danger, however at night it was nearly impossible to see a red stop sign in a poorly lit area. Over time, materials changed to become more reflective and in 1954 red stop signs became the norm. 

In 1920, the first electric three-color traffic signal was developed in Detroit. It used the color yellow for the first time. Prior to then, only red and green traffic lights were used on the roads. A few years later, Garrett Morgan of Cleveland, Ohio, patented the three-position traffic signal. The patent was later purchased by General Electric for $40,000. 

Why the color green? 

The color green is synonymous with “go”.  We can thank the early design of the semaphore system for this association. In the 20th century, the word “go” replaced “caution” and was painted white on a green background. When the device was later electrified, the colors stayed but the words were removed.

Traffic Lights: Fun Facts and Recent Findings

What do you do when you’re Color Blind? 

Ever wonder how those who are color blind manage red-yellow-green traffic lights?  How can they tell when to stop and go?

We discovered that far more people than we thought have trouble distinguishing colors – in the US, one male in every 12, but only one woman in every 200. In total, there are about 15 million color-blind Americans.

There is no cure for color blindness and it varies in severity. In nearly every case, color-blind people retain blue-yellow discrimination, and many have some red-green discrimination. Color blind people of course ‘see’ red lights by their position – a bright top light of the three means ‘red’. In Eastern Canada, traffic lights are mounted horizontally and are purposely differentiated by shape to help those who are color blind (each light has its own shape). The US has not adopted this. There have been innovative ideas to help color-blind people in the context of ‘smart cities.”

The Disadvantages of Traffic Lights:

Traffic lights help create a more orderly flow of vehicles traveling through intersections, although they can have adverse effects on traffic safety, “While many people realize that traffic signals can reduce the number of angle collisions at an intersection, few realize that signals can also cause an increase in other types of accidents. For example, it has been well documented that other types of accidents, notably rear-end collisions, usually increase when a signal is installed.” 

In 1982,  Philadelphia removed traffic signals at 222 intersections that were not warranted, and cut crashes. By 1992, over 800 traffic lights had been removed, cutting crashes at these intersections by 60%. 

Smarter Traffic Signs?   

Traffic lights are obsolete; it is time to enter the digital age. Take Amsterdam for example, where sensors detect traffic volume and operate red-green lights accordingly to keep traffic moving.  

When all vehicles are capable of speaking to one another, in real-time, especially at intersections, we can begin to dismantle many thousands of traffic lights – and thank them for their 142 years of service. 


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