View Details

Did you ever wonder why our street stoplights designate red as &#;stop&#; and green as &#;go?&#;

Well, in the s the British railroads adopted a flag, lamp and semaphore signal system where red meant danger, white meant safety and green indicated proceed with caution. They took their inspiration from early industrialization where factory machines used red to indicate the equipment was off and green when turned on.

But one time the red glass lens on a signal lamp dropped out of its socket, showing a white light, which then caused a rail collision. Traditionally red has evoked danger and green, a more calming influence. But it was optical science that reinforced the choice.

Red has the longest wavelength in the visible spectrum and is less likely to be interfered with by other light sources in what&#;s known as &#;light scattering.&#;  Think of fog or dust in the air. Red light penetrates best.

By the s traffic conditions in London prompted officials to seek a way of controlling horse-drawn carriages with a signal system and opted for the railroad scheme of color-coded semaphores and lights controlled by a policeman, often perched on a raised kiosk in the middle of the intersection.

You can credit American police officer William Potts for the invention of the first traffic lights in Detroit in . But back then they were still sequenced by an officer, making traffic control expensive. Eventually, a timer system was introduced to sequence the flow. But there was also a system activated by sound.

A microphone was installed on the light pole and when a car approached it would honk its horn and the light would turn green&#; but just for ten seconds to allow that one car to get through. You can imagine the problem that was going to create.

Today we use not only timers but some sophisticated measuring devices to sequence traffic lights, including inductive loops.  You&#;ve probably seen signs of them, buried in the pavement, as you pull up to an intersection,.  They measure the metal in cars as they drive over them, allowing the system to know that a car is there waiting for a green signal.

Link to FAMA

Even the traffic lights themselves have improved.  They now measure either eight or 12 inches in diameter and must be visible in every lighting condition.  The older incandescent bulbs that illuminated them use to burn at 175 watts and needed constant replacement.  Now they&#;re being replaced with high endurance LED lamps which give as much light but only require 10 &#; 25 watts of electricity.

At many Connecticut intersections there are also sensors on the light poles detecting the strobe lights or special radio signals emitted by emergency vehicles, giving them the right of way.

To help the 13 million Americans who are color blind, stoplights are always arranged with red on top and green on the bottom.

Given the sophisticated technology and engineering time spent on designing a stoplight system for an intersection, they&#;re not cheap.  A fully equipped setup can cost between $250,000 and a half-million dollars with an annual maintenance cost of $8,000.  That&#;s why towns and CDOT are so reluctant to add new lights, despite requests.

Have you ever been puzzled with the thought as to why blue doesn&#;t indicate go and brown denotes a halt? More than simply traffic lights have been influenced by the concept that red indicates halt and green signifies go.From an early age, we&#;ve been taught that the color red denotes danger and the color green denotes that it&#;s safe to proceed. But why were those specific colors picked for traffic signals? It turns out there&#;s a perfectly reasonable answer.

The Early Traffic Lights

Because of an increase in traffic on the road, the first traffic lights were built in the United States. Concerned about traffic accidents, towns and cities would construct traffic towers to assist traffic flow. Officers stationed themselves in the towers, blowing whistles and flashing red, green, and yellow lights to alert traffic when it was time to stop and go.

William Potts invented the first tri-color, four-direction traffic light in . This made it easier for cars to stay safe at junctions. But, there were still a number of traffic signal and pattern systems in existence around the country. The Federal Highway Administration published &#;The Manual on Consistent Traffic Control Devices&#; in to define uniform standards for all road signs, pavement markings, and traffic signals, mandating them to all employ red, yellow, and green light colors.

History of the colors

There were traffic signals for trains before there were traffic lights for cars and other automobiles. Railroad firms used red to indicate stop, white to indicate move, and green to indicate caution at first. Train conductors, as you might imagine, had some issues with the color white indicating go &#; bright white could easily be confused for stars at night, leading train conductors to believe they were all clear when they weren&#;t.

Because it&#;s easy to differentiate from the other colors, railway companies finally adopted the color green to signify go, and the color yellow to imply continue with caution, and it&#;s been that way ever since, and when traffic lights were installed, it became standard for them as well.

Why are these colors chosen?

• We recall that the seven colors of the light spectrum are VIBGYOR (Violet&#;Indigo&#;Blue&#;Green&#;Yellow&#;Orange&#;Red), specified with the wavelengths increasing in order. Violet has the shortest wavelength, whereas Red has the longest. Also, longer wavelengths have shorter frequencies and tend to travel larger distances when encountering obstructions.
• If different colors are considered, red has the longest wavelength, followed by yellow, and finally green. The colors with the longest wavelengths are chosen for Signals because longer wavelengths may go a greater distance. Because Orange looks too much like Red in bright light, it might cause confusion. As a result, Red light can travel the greatest distance in rain, fog, and mist, and remains visible the majority of the time since it has a high priority, followed by Yellow, and finally Green.
• The three signs of traffic light: Stop. Caution and Go, were assigned in order of priority to be notified to the driver. Stop, for instance, should be alerted to a driver as soon as possible so that he may respond and come to a complete stop . As a result, it was assigned the red color, which has the longest wavelength and can thus be seen from a great distance. Similarly, the Caution sign was chosen next.Because yellow has a little shorter wavelength than red, it was used to warn drivers. School zones, some traffic signals, and school buses are still painted yellow since it is visible at all hours of the day. This was followed by the Go sign which was assigned green color , as per its wavelength, which comes after yellow color.

Long before vehicles were ever invented, the color red has always been associated with danger. Because red has the longest wavelength of all the colors, it can be seen from a longer distance than the others. Hence it has been assigned STOP signal, and other colors , Yellow and green are used to signify Caution and Go respectively as per their wavelengths. There&#;s science in everything, you know!

Want more information on traffic light red and green? Feel free to contact us.