Have you ever stopped to wonder why traffic lights use red, yellow, and green? The choice wasn’t arbitrary. It was carefully selected based on existing signals in the railroad industry. Let’s dive into the history and logic behind these colorful cues that govern our roads.
The Railroad Roots
Before cars clogged city streets, trains ruled the rails. Railroads in the mid-19th century faced the challenge of coordinating train movements to prevent collisions. Early signaling systems relied on simple color-coded flags and lamps. By the late 1830s, a basic system was in place using red to signal “stop” and green to indicate “proceed with caution”. There was no yellow at this point.
Red was chosen for its long-standing association with danger, a universal warning recognizable even then. Green, on the other hand, was a natural choice for safety and clearance.
The Problem with Green
The initial two-color system worked… until it didn’t. Accidents occurred when red lenses broke or fell out, leaving a white light shining. Engineers, seeing white, mistakenly thought the track was clear and proceeded, sometimes with disastrous consequences. The solution? Introduce a third color: green would be used to indicate “clear” and white was removed from use entirely. But that still left the need for a ‘caution’ signal.
Enter Yellow
The addition of yellow as a warning signal came later, adapted from railroad practices. Yellow provided an intermediary stage, alerting engineers (and eventually drivers) to prepare to stop. The first electric traffic light, installed in London in 1868, actually followed this red and green railway model and sadly exploded after only a month, injuring the police officer operating it.
From Rails to Roads
As automobiles gained popularity in the early 20th century, the need for traffic control in urban areas grew. Early traffic lights mimicked the railroad signals, adopting red for stop and green for go. Yellow was gradually integrated as the standard caution signal. One of the first electric traffic lights in the U.S. was installed in Salt Lake City in 1912, using red and green lights. The yellow light followed a few years later.
Why These Colors?
Beyond historical precedent, the choice of colors also considers human perception. Red has the longest wavelength and thus is most easily seen from a distance, even in fog or rain. Green and yellow offer sufficient contrast and visibility, making them suitable for clear signals. Interestingly, some studies suggest that our sensitivity to green light is higher than to other colors, which might contribute to its association with “go.”
Traffic Light Trivia
- The first traffic lights weren’t electric; they were gas-powered.
- Garrett Morgan, an African American inventor, patented a traffic signal with a third position – an early version of the yellow light.
- Some cities experimented with blue lights instead of green, but the idea didn’t catch on due to visibility issues.
The Takeaway
The next time you’re waiting at a red light, remember that the colors aren’t random. They’re the result of a long evolution, shaped by railway history, safety concerns, and even a bit of trial and error. From trains to automobiles, the familiar red, yellow, and green guide us safely on our way.