Traffic lights are red, orange, and green because these colors are easily distinguishable by drivers and have universal meanings: red for stop, orange for caution, and green for permission to proceed.
First, the choice of red to indicate stop comes from the railway domain, long before the existence of cars. In the era of steam railways, a clear signal was crucial: it needed to be visible from a distance and without confusion. The red, associated with danger and blood, immediately attracts the human eye: perfect for stopping any movement abruptly. The green, on the other hand, was practical because it was very different from red, easy to discern, and already well established in railway codes. It meant "clear track" – all is well, off we go. The orange or amber-yellow came later, around the early 20th century, because there was a need for an intermediate color to clearly indicate "caution, changes are coming soon." It quickly became clear that the human eye easily spots these three distinct colors, even from a distance or in difficult conditions. The red-orange-green combo was therefore ideal for effectively regulating the growing traffic of motorized vehicles.
The choice of the colors red, orange, and green is based on their instinctive meaning easily grasped by our brain. Red automatically evokes an alert and danger. This is due to its powerful wavelength that makes it immediately visible and quickly attracts our attention, as the human brain is, in a way, wired to notice it first. In contrast, green conveys a spontaneous idea of safety, freedom, or a clear path, particularly associated with nature and calmness. Between the two, orange naturally positions itself as a middle ground that expresses a transition, a clear warning encouraging caution without necessarily stopping abruptly. This instinctive interpretation, shared across cultures, allows these colors to effectively communicate an instant, intuitive, and universal message—there's no need to think for ages when you see the light turn red!
Traffic light colors are not chosen at random: they follow an international standard defined by the Vienna Convention on Road Signs and Signals of 1968. This document specifies that red always requires a complete stop, green explicitly allows passage, and amber asks drivers to slow down, unless they are already too committed to stop safely. Each shade is coded to avoid confusion, regardless of the country. Moreover, these rules are regularly checked to ensure that the color is always clear, well-visible, and identical wherever one drives, so that no one ever wonders: "Is this one dark green or light green?"
The choice of red, orange, and green is also rooted in our social habits and cultural codes. Red, for example, is everywhere associated with danger: it immediately grabs attention because our brain is accustomed to spontaneously linking it to risk or prohibition, like a "stop" sign or a fire alarm. Green, on the other hand, is generally perceived as positive: associated with safety, nature, or free movement, it is intuitive to assign it the notion of an open passage. Orange, in between, has this intermediate aspect: it suggests caution, slowing down, or vigilance, without really prohibiting. These color codes are so embedded in our daily lives that they become almost automatic; they are culturally established, implicit, and deeply rooted in our spontaneous way of perceiving the environment around us.
The red and green colors were initially chosen for railway signals due to their maximum visibility at long distances. Today, these colors have become universal for road traffic.
Nearly 1 in 12 people in the global population suffers from color blindness, having difficulty distinguishing these colors. That’s why the position of traffic lights (red at the top, amber in the middle, green at the bottom) remains unchanged to ensure safety even in cases of difficulty identifying colors.
In Japan, the green light is often described by the word 'ao', which means blue? This description stems from a historical linguistic peculiarities of Japanese, distinguishing colors differently compared to Western languages.
In some countries, countdown timers are integrated directly into traffic lights to clearly indicate the remaining waiting time. This initiative could help reduce driver frustration and improve traffic flow.
The colors red, orange, and green are standardized almost everywhere, according to international recommendations. However, in some rare cases, such as in Japan, green may have a slightly bluish hue for specific cultural and linguistic reasons.
Colorblind individuals often have difficulty distinguishing certain colors, particularly red and green. To address this issue, traffic lights are always installed in a predefined order (red on top, orange in the middle, green on the bottom or horizontally in that order) so that colorblind people can clearly differentiate the phases of the light.
These standards are defined and recommended by international organizations such as the UN (Vienna Convention on Road Signs and Signals) and ISO (International Organization for Standardization). Each country then commits to applying these standards in accordance with its local legislation.
Modern electric traffic lights were introduced in the early 20th century. In particular, the first traffic light of this type was installed in 1914 in Cleveland, United States, gradually setting the standards that are still in effect today.
Historically, red is associated with alertness and danger due to its high visibility. It is also linked to blood, passion, and urgency in many cultures, which reinforces its immediate interpretation as a safe stop signal.
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