Fact of the Matter: Traffic Lights

By: C.G. Hoffman

Red light, green light, one two three… The three colors of traffic lights seem to be universal, but who decided which colors they would be? And how long have they been around?

Traffic control is not a new problem; it’s as old as transportation itself. As soon as people stop using their feet as their primary mode of getting around, problems arise, namely, traffic. Ancient Rome dealt with congestion in the capitol by forbidding the use of chariots in the city during daytime hours. Charioteers, no matter how important their passengers, had to park their chariots at the city gates. They did have slaves to shlep them around on hand-carried litters, though. (So Governor Hochul and her Midtown congestion plan is not that original after all!)

The first traffic light was a total bust: literally! It was installed at a busy intersection in London in 1868, but the gas-lit apparatus exploded, killing the police officer who operated it.

The first electric traffic lights were invented in 1912 by a police officer in Salt Lake City. He simply dipped light bulbs in red and green paint, mimicking the colors used for railroad lights, and attached them to a wooden box. The box was then attached to a pole and connected to the existing wires used for the trolley system. A policeman nearby controlled the lights with a switch.

In the early 20th century, New York City had become a traffic nightmare. Horses, carriages, pedestrians, street cars, bicycles, and the new automobiles all competed aggressively in the heavily congested streets. Accidents were a common occurrence, and for the high end department stores that started cropping up, bad traffic meant bad business.

In 1920 NYC received its first traffic light, on 42nd Street and Fifth Avenue. It boasted two colors, using green for “Stop” and white for “Go!”

Early traffic lights used a variety of colors for their signals, but the red-green system that has been almost universally adopted all over the world is largely based on railroad signals.

How did yellow lights come to be? The two light system didn’t give drivers any warning, and accidents were common on busy city roads. The yellow light was first added in Denver in 1920 and was quickly popularized worldwide as the number of accidents dropped sharply.

Red light has a longer wavelength than other colors, so it can be seen from farther away.

The green light isn’t fully green; it can contain blue bulbs to help those with color blindness. Unless you’re planning a trip to Japan, where blue is standard.

Today’s urban traffic lights are controlled by a sophisticated computer system that uses cameras and sensors embedded in the pavement to transmit real-time data across the network, so red lights can be adjusted for rush hour or to improve traffic flow. New York City has a total of 7,660 (out of 12,460) signalized intersections that are controlled and managed by traffic management centers.

According to the AAA, the average American spends 58.6 hours each year waiting at red lights.