Traffic lights are a common thing these days, and you, like all other drivers, are required to follow the rules: stop at a red light, prepare for a yellow one, and pass on a green one.
There is no doubt that traffic lights should be in densely populated cities. Be that as it may, this is the only way to control traffic when there is no police nearby.
Riding every day from home to office, we can’t even imagine a road without at least one traffic light, but there were times when traffic lights didn’t exist at all. Of course, the roads were relatively free...
So, as already mentioned, when you get behind the wheel, you must adhere to certain rules. Traffic lights are the same all over the world and consist of three different colors that have their own specific purpose. But how did it happen that the traffic light is exactly red, yellow and green? Why isn't it purple, brown and grey? There are several suggestions on this topic, but first a little history.
It's no secret that the automotive industry pioneered many important things that are still used around the world today, but in turn, it had to borrow something from other industries. A good example is a traffic light.
The first traffic light saw the light in 1868 in London. It was used exclusively to manage rail traffic at the intersection of George and Bridge Streets. The design was quite simple, but performed its function very well. It was made up of two vertical switches that could change to a horizontal position to indicate to trains that they should stop. At a 45-degree angle, the system meant what yellow light does today: attention.
And now the most interesting thing: since the signaling device was completely invisible at night, the engineers decided to install primitive lights on it that would display the "stop" and "attention" modes. What was their color choice? Red for "stop" and green for "attention".
You are probably wondering how the green light became a signal for "attention"? Well, no one knows for sure, but that all changed a few years later when traffic lights made their way into the automotive industry.
A very important moment happened in 1912 in the USA (where else?) thanks to Lester Farnsworth Wire, in charge of traffic in the Salt Lake City Police Department. The first manually operated traffic light had only two colors: red and green. Although at that time there were practically no cars on the roads and the rules of the road had not yet been prescribed, the drivers were surprised by the new invention, so the presence of a policeman was necessary to force them to obey the device.
The first three-color traffic lights appeared again on the railway, but the trio was slightly different: red for "stop", green for "attention", white for "free". While the first two have a more or less obvious meaning, the white signal has become a headache for the authorities. Similar lights, whether they were stars or street lights, misled the drivers, leading to fatal collisions.
Why are traffic lights red, yellow and green
The color red is most often associated with blood and thus was chosen as a prohibitory signal. Symbolizing a dangerous situation leading to serious consequences, red has always been chosen as the color to encourage vehicles to stop and thus avoid accidents.
As for green, color symbolism also became the reason for its use. As with red, green is the source of human emotion. It is associated with something relaxing (such as nature) that will not have a powerful negative effect on drivers. In addition, the green color is easy to recognize at night.
The choice of yellow was surprising. Many believe that it symbolizes the sun, which is also considered a relaxing and at the same time attention-grabbing element.
Traffic lights have evolved over the years, especially in terms of their effectiveness for colorblind people. Commissioners in many countries have dealt with this issue in different ways, whether it was traffic lights with double red light or sections of different shapes. One way or another, the classic design had to be slightly changed.
Since color blindness is one of the most common forms of visual impairment, these days a little orange is mixed with red - in this case, color blind people are able to notice a brake light. For the same purpose, a shade of blue is added to green.
Why are traffic lights red, yellow and green
Why does a traffic light have these three colors - red, yellow and green!?
Why did the choice of colors for traffic lights fall on red, yellow and green? It is believed that this is due to two main reasons. One of them is in the field of phenomena of physics, the other in the field of human psychophysiology.
Let's first turn to the history of the creation of a traffic light, and so:
The inventor of the first electric traffic light is Lester Wire from Salt Lake City (Utah, USA). In 1912, he developed, but unfortunately did not patent his own, a traffic light with two round electrical signals, red and green.
On August 5, 1914, in Cleveland, Ohio, USA, the American Traffic Signal Company installed four electric traffic lights designed by James Hoag at the intersection of 105th Street and Euclid Avenue. They had a red and green signal and, when switched, emitted a sound signal. The system was controlled by a policeman sitting in a glass box at an intersection. Traffic lights set traffic rules similar to those adopted in modern America: a right turn was carried out at any time in the absence of interference, and a left turn was carried out on a green signal around the center of the intersection.
And only in 1918, to the two colors of the traffic light - red and green, another color was added - yellow. Tri-color traffic lights using a yellow signal have been installed in Detroit and New York.
James Hoag's traffic light system (drawing from patent)
In Europe, similar traffic lights were first installed in 1922 in Paris at the intersection of Rue de Rivoli and Sevastopol Boulevard. Back in Hamburg on the Stephansplatz square, as well as in England - in 1927 in the city of Wolverhampton.
In the USSR, the first traffic light was installed on January 15, 1930 in Leningrad at the intersection of avenues on October 25 and Volodarsky, now Nevsky and Liteiny avenues. And the first traffic light in Moscow appeared on December 30 of the same year at the corner of Petrovka and Kuznetsky Most streets.
In connection with the history of the traffic light, the name of the American inventor Garrett Morgan is often mentioned, who patented an original traffic light in 1922. There is a persistent myth about Morgan's great influence on the development of traffic lights, but in reality he is only one of many inventors of various traffic lights of the early 20th century.
Well, that's why Lester Vayre chose these colors, perhaps, first of all, he was guided, of course, by the psycho-physiological perception of color by a person - red as a danger and prohibition, and green as calmness and resolution. But is this really so, let's turn again to the history and research of many inventors of the first traffic lights and their observations of the propagation of light, of different spectra, in the air.
Let's consider all the factors on which these three colors were chosen - red, yellow and green!
PSYCHOPHYSIOLOGY.
As already mentioned, the first is psychophysiology - colors affect differently in their expressiveness.
In many publications on this topic, and even on the Internet, statements are published that the red color is often in nature for many living beings a signal of a very close danger. This is very strange - because scientists have proven that most animals are color blind and do not distinguish colors. Well, further - according to these "publications" that the opportunity to run over a pedestrian is a dangerous situation for two participants on the road and the red signal excites the nerve centers of the driver and the pedestrian, indicating the presence of an imminent danger! Perhaps, but still, let's explore this topic further.
It is further stated that it is these three colors that are most well perceived by the human eye in terms of their physical parameters and the wavelength inherent in them. Yes, this is exactly so, because these three colors have the largest, if I may say so, wavelength. Here's a look at the visible spectrum of colors.
From the above figure, we see that our - red, yellow and green colors are at the very beginning of the visible spectrum, respectively, have the longest wavelength.
Next, we will tell you what we brought this example to, but for now we will continue to consider further explanations of what the publications write. Further, it is explained to us that the color perception of red and green signals, as forbidding and forbidding movement, must be clearly identified without the possibility of error. What is observed. Even color-blind people who do not understand colors by the tone of gray can accurately react to the color of a traffic light red or green! Hm! Why, then, is it forbidden to have a driver's license with such a disease!? - the question immediately arises! But the articles are quickly rehabilitated and explain it in such a way that - “... although this definition of a person’s physical defect of vision is greatly weakened. Therefore, there is a ban on driving with such a disease ... ".
Well, the following explanation about the green color: “... it should be clearly understood that a person’s vision of light of different wavelengths of light reacts with greater or lesser sensitivity. The choice of resolving green light is due to the maximum approximation of this color to the level of the most clearly perceived part of the spectrum. It is visible in contrast to other traffic light colors from the greatest possible distance, because the highest sensitivity of the eye is at 555 nm. And the perception of green color, which has a range of values of 500-550 nm of the spectrum, at different times of the day does not fall below 0.5 of the maximum sensitivity value, both in daytime and twilight observation ... "
Here we disagree a little and explain why we gave the above example with the visible color spectrum.
PHYSICS OF COLOR. DIFFUSION.
In fact, the colors green, yellow and red were chosen in the design of the traffic light in part because red is perceived as danger, yellow as focus, and green as permission. The question was in the range of visibility under different weather conditions. And such a concept as light scattering was taken into account.
Such a concept as Rayleigh scattering was taken into account. What it is!? It is the elastic scattering of light or other electromagnetic radiation by objects or surfaces much smaller than the wavelength of the incident light. This can often occur on clear solids and liquids, but is more common in gases. This type of scattering occurs in the blue of the sky during the day. Rayleigh scattering is inversely proportional to the fourth power of the wavelength, meaning that shorter wavelength blue light will be scattered more strongly than longer wavelengths (such as green and red). which was taken into account. This dependence was deduced by the British physicist John Rayleigh back in 1871. All the inventors of traffic lights based their choice on this dependence, because we know the air both day and night contains drops of suspended liquid. For this reason, Rayleigh scattering was taken into account.
Those. everything is much simpler than the perception of colors. It's all about the physics of color. From the figure, we can see that the red, yellow, and green colors scatter less than the other colors. From this we can conclude that in bad weather - fog or rain, the red color of the traffic light will be visible the farthest, the yellow will dissipate a little faster, and the green will be visible at a lesser distance than its two "older brothers". Personally, as a person who is simply interested in everything, I was very surprised by the many publications on the Internet that I initially read when preparing this article, stating that it is the green color that will be seen the farthest! But based on the physics of color and John Rayleigh's dependency, we see that it will be quite the opposite!
So the reason for choosing these three traffic light colors turns out to be much more mundane than others imagine - namely, in the properties of different colors and their dispersion in the air! People were worried about road safety and the visibility of traffic signals over a longer distance under various weather conditions - whether it be clear weather, fog or rain (which England is rich in), snow, hail and other weather phenomena, the light from the "traffic controller" of the traffic light should be seen as far as possible!
I think if the blue color - the color of calmness, dissipated the worst of all and was visible at a longer distance, then the choice would have fallen on this color, and not on red. And here the formula of "color danger" would not fit.
The order of alternation of traffic lights corresponds to the international Convention on Road Signs and Signals. Traffic lights alternate in the following sequence: red - red with yellow - green - yellow - red. Alternation of signals red - green - yellow - red or red - yellow - green - yellow is allowed.
A red solid signal prohibits movement across the entire width of the carriageway. Varieties of the red signal:
A contour black arrow on a red background of a round shape prohibits movement in the direction of the arrow;
An oblique red cross prohibits movement along the lane over which it is installed;
The red silhouette of a man forbids pedestrian traffic;
Red flashing prohibits entry to a railway crossing, bridge, pier, etc.
A yellow solid signal obliges all drivers to stop before the stop line, with the exception of those who could not stop before the intersection.
Yellow connected to red warns that the green signal is on.
A yellow flashing signal warns of the presence of an intersection and does not prohibit movement.
A green steady signal in the absence of any additional sections of the traffic light allows movement along the entire width of the carriageway in all directions.
Varieties of green signal:
A black arrow on a green background of a square, round shape, as well as a green arrow on a black background of a round shape - permission to move in the direction of the arrow;
A green arrow on a black background of a square shape, pointing down, allows movement in the lane over which it is installed;
A signal in the form of a green silhouette of a person allows pedestrian traffic;
The green arrow of the additional section of the traffic light allows movement in the direction of the arrow, regardless of the signal of the main traffic light;
A flashing green signal warns of the end of the enable signal.
Permission for the movement of public transport depends on the combination of the included signals of the upper and lower rows of a special traffic light. Turning on the lower signals movement is prohibited in all directions.
Studies have shown that there is a so-called critical section before the intersection and, being within this section, the driver cannot stop in time in front of the stop line when changing the permissive signal to prohibitive.
The critical section is defined as the distance from the stop lines to the point where 10% of drivers cannot stop. The length of the critical section depends on the speed of movement. So, at a speed of 50 km/h, the length of this section is 43 m and the travel time for this section is 3.1 s; at a speed of 60 km - the length of the section is 58 m and the travel time is 3.5 s; at a speed of 80 km - the length of the section is 91 m and the travel time is 4.1 s.
Hence, the travel time of the critical section at different speeds varies within 3-4 s. This prompted us to use a flashing green signal as a warning and take the flashing time equal to the time of passage of the critical section. In order not to reduce the throughput of the intersection. with a permission signal, a green flashing signal is introduced in part at the expense of the duration of the yellow, which will allow you to safely pass the intersection.
Types of traffic lights. Traffic lights are classified according to their functional purpose - transport and pedestrian; by design - one, two-section, three-section and three-section with additional sections; according to the role performed in the process of motion control - the main ones, backups and repeaters.
The main two groups of traffic lights: transport and pedestrian, which in turn are divided into types. There are 8 types of traffic lights and 2 types of pedestrian ones. The first traffic light number means the group, the second number - the traffic light type.
traffic lights Type 1 have three round signals with a diameter of 200 or 300 mm, arranged vertically or horizontally.
The first type is used with additional sections, in which arrows indicate the direction of movement (arrows on a black background). Traffic lights of this type are used to regulate all directions of traffic at intersections. Their use is allowed at railway crossings, intersections with tram and trolleybus lines, in narrowings of the carriageway, etc.
Traffic lights 2 types. On the lenses of the traffic light, the contours of the arrows are applied. indicating permitted or prohibited movement. In this case, the green signal (arrow) is applied on a black background. Type 2 traffic lights are used to regulate traffic in certain directions (indications on the arrow lens).
Traffic lights type 3. They are used as repeaters and in conjunction with type 1 traffic lights.
They are installed under the main traffic light at a height of 1.5-2 m from the roadway. The diameter of the signals is 100 mm. If the main one has an additional section, then the repeater will be equipped with an additional section. Traffic lights of this type can be installed to control cycling.
Traffic lights type 4. They are used to control entrances to separate traffic lanes, with reverse traffic.
They are installed above each lane at its beginning. They have a horizontal arrangement of signals; on the left - in the form of an oblique red cross, on the right - in the form of a green arrow pointing downwards. Both signals are performed on a black rectangular background. Overall dimensions 450 x 500 mm.
These traffic lights can be used together with type 1 traffic lights if the reverse traffic is not organized across the entire width of the carriageway. In this case, the type 1 traffic light does not apply to lanes with reverse traffic. This lane may be delimited by a double broken line 1.9 when the type 4 traffic light is turned off.
Traffic light type 5. Has 4 signals of pale moon color of a round form with a diameter of 100 mm. This traffic light is used in cases of conflict-free regulation of the movement of trams, shuttle buses, trolleybuses moving along a specially allocated lane. In the scheme of organizing traffic at the intersection, a conflict-free passage is provided, i.e., the indicated types together with the general flow, therefore, there is no need to use this type at the intersection.
Traffic light type 6. It has two (or one) round red signals with a diameter of 200 or 300 mm, located horizontally and operating in the alternate flashing mode. When the signals are off, movement is allowed. They are installed in front of railway crossings, drawbridges, berths, ferry crossings, in places where special vehicles enter the road.
Traffic light type 7. It has one yellow signal, constantly working in flashing mode. It is used at unregulated intersections of increased danger.
Type 8 traffic lights. They have two vertical signals of red and green colors of round shape W 200 or W 300 mm. They are used for temporary narrowing of the carriageway, when alternate traffic is organized along one lane. They are also used to control low-intensity traffic in the internal territories of garages, enterprises and organizations where a speed limit has been introduced.
Pedestrians have two vertically arranged signals of a round or square shape with a circle diameter or a square side of 200 mm or 300 mm. All pedestrian crossings at the intersection controlled by traffic lights are equipped.
Traffic lights with a large size are installed on the main streets, squares, on roads with the speed of T.S. 60 km/h
Traffic light design. The traffic light consists of separate sections (Fig. 1) and each section is designed for a specific signal. Depending on the type of traffic light, the sections have different shapes, symbols, light sources, etc. Common to all sections is the presence of an optical device placed in a separate housing.
Figure 15 - Traffic light device
The sections are interconnected by threaded hollow bushings 1, through which the supply wires are passed. The section consists of a body 8, a sun visor 4 and a cover 6. They are made of sheet steel or plastic. An optical device is mounted in the cover, which consists of a reflector 7, a colored diffuser lens 3 and a movable glass 10 with an electric lamp. When the glass is moved, the filament of the lamp is set at the focus of the reflector. To connect the current supply at the bottom of the section there is a block 9.
Light source.
As a light source, incandescent lamps are used, both for general and special purposes. So, gas-light tubes or emitting diodes are used as a light source. The main disadvantage of an incandescent lamp - for general use - is the large length of the filament, which is difficult to focus, low vibration resistance of the lamps, and also have a short service life (500-800 hours):
It has been proven that filament burnout occurs mainly due to inhomogeneity in wire diameter, helix pitch, electrical resistance and evaporation rate.
In some traffic light designs, halogen lamps are used. At small sizes, they have an increased specific light output and a compact filament, and these lamps focus well. However, these lamps were not widely used due to their high cost.
Two simultaneously working lamps can be used in one section, but this requires the installation of a special reflector and a bifocal lens. Such a solution is associated with a complication of the design and an increase in cost.
Abroad, a curved gas-light tube has found application as a light source. The tubes contain a filler of red, yellow or green colors, which eliminates the need for a colored lens. For the glow of the tubes, a voltage of over 2000 V is required, so a transformer is required. They have a long service life, but in terms of signal strength they are 5-6 times inferior to modern traffic lights with incandescent lamps.
Traffic light lenses.
In recent years, plastic lenses have become widespread in our country and abroad. They have advantages over glass ones in ease of manufacture, higher strength under impact and vibration loads, as well as less weight (about 3 times). These lenses are usually made from polycarbonate.
Diffuser lenses are designed to redistribute the light flux into space. To do this, a patterned, rhombic, prismatic or drop-shaped pattern is formed on their inner side. For modern lenses, this angle is in the range of 5-15°, which ensures normal visibility of the signal on multi-lane roads (100 m).
Reflector.
The reflector is characterized by two main internal surfaces: paraboloid, which provides the concentration of the light flux, and conical (or cylindrical), designed to increase the depth of the reflector and thereby reduce the burnout of the lens dye.
With a short focal length, there is a danger of a false traffic signal (phantom effect), when the beam from an extraneous light source, hitting the reflector, returns to the observer again.
In the designs of modern reflectors, the focal plane AA is brought as close as possible to the plane of the light hole, behind which the non-working conical surface begins.
As a rule, the condition is met:
(13)
where: is the diameter of the light aperture of the reflector, mm.
Reflectors are made of steel, aluminum alloys or plastics with subsequent processing of the inner surface. Plastic reflectors with a working surface obtained by vacuum deposition are widely used.
Anti-phantom devices.
An anti-phantom device in a traffic light is a sun visor, but at a low position of the sun (for example, east-west, west-east), all traffic lights may glow.
There are several methods to eliminate the phantom effect, but they require a change in the design of the reflector or traffic light lens.
The reflector with the so-called anti-phantom cross consists of mutually perpendicular segmented plates with slots for the location of a halogen lamp (Fig. 1).
A beam of light falling from an external light source onto the reflector is deflected and absorbed by the surface of the plates. Another solution is carried out by installing a special anti-phantom lens in front of the light filter 1, consisting of two parts 2, 3, each of which has a sawtooth profile (Fig. 2). A ray of the sun, falling on an inclined surface, is thrown onto a horizontal blackened step and absorbed by it.
Rice. 16 - Anti-Phantom Cross
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Fig. 17 - Lens that absorbs the sun's rays
A modern person in his life is surrounded by many everyday objects that seem so familiar and unchanging to him that he does not even think about the fact that they once did not exist, and that someone created them. The foregoing fully applies to such a familiar device as a traffic light. His story began a long time ago, and while he acquired a familiar look to all of us, a lot of time passed.
The appearance of the first traffic light
The first device designed to regulate traffic by giving its participants special signals appeared back in 1868. It was then that such an apparatus was installed near the building of the English Parliament in London.
It was created by railway engineer John Peak Knight, who used for this his experience with railway semaphores, which worked on a principle similar to a traffic light.
Naturally, the first copy of the traffic light was not like its modern counterparts. So it was controlled manually, and its design was the simplest: two semaphore arrows that could move freely in a vertical plane.
At the same time, the arrow in a horizontal position indicated the requirement to stop, and if it rose up to 45 degrees, this meant a warning that road users would move with the utmost care.
At night, the traffic light used a gas lamp with colored illumination for its work, while the red light meant the order to stop, and the green light meant permission to continue further movement.
The first traffic light in the history of mankind was installed on a pole six meters long and was intended to facilitate the crossing of the road for pedestrians and its signals were not intended for them, but for vehicles traveling on the roadway.
Unfortunately, the fate of the first traffic light was unsuccessful: in 1869, the gas lamp in it exploded and injured the policeman who was driving it. After this incident, it was dismantled and for the next 50 years not a single traffic light was installed in London.
Creation of automatic traffic lights
The main drawback of the first traffic lights was the fact that a person was required to control them. It is clear that under such circumstances it was impossible to provide a large number of streets in cities with traffic lights. Therefore, the inventors directed their efforts to the creation of automatic devices for traffic control.
It is believed that the first such system was created by Ernst Sirin, who received it in 1910. At the same time, she used a system of signs with the inscriptions “Stop” and “Proceed”, which, respectively, prohibited and allowed movement. This system did not use backlighting, which made it difficult to use at night.
In its modern form, the traffic light was created in 1912 by an inventor from Utah, Lester Weir. He already worked on electricity and had two round lamps of green and red. True, Vayr did not patent his design.
However, the massive use of traffic lights on city streets began when four traffic lights were installed at once in Cleveland, Ohio, on August 5, 1914, by the American Traffic Light Company. They were located at the intersection of 105th Street and Euclid Avenue, and their creator was James Hogue.
These devices also had two electric lights, and when switched, they emitted a sound signal. The work of the apparatus was controlled by a policeman, who was in a special glass booth, standing at the crossroads.
Devices that have the familiar three-color color scheme appeared much later, in 1920, on the streets of New York and Detroit. Their creators were John F. Harris and William Potts.
Europe was somewhat behind the United States in the process of "traffic lights" and the first electric traffic light appeared there in France in 1922, and in England this device was installed only in 1927.
In the Land of Soviets, the first traffic light was installed on January 15, 1930 in Leningrad. They put it at the intersection of Nevsky and Liteiny avenues. In the capital of the country, this traffic control system was installed a little later - on December 30 of the same 1930. They placed it at the corner of Petrovka and Kuznetsky Most. The third city equipped with a traffic light was Rostov-on-Don.
All these traffic lights were installed as an experiment, and after its completion in Moscow alone, by the end of 1933, about a hundred such devices were installed.
At the same time, the traffic lights of that time differed from those familiar to us in that they used the principle of operation of a mechanical clock, where the arrow did not point to the time, but to a colored field indicating the mode of movement. They were quickly replaced with electric lamps familiar to us with a vertical arrangement of lamps, however, they were not the same as we are used to. The fact is that the arrangement of colors in this design was not usual, but inverted: green came on top, then yellow and red.
The very word "traffic light" entered the Russian language in 1932, when it was included in the Great Soviet Encyclopedia.
The device of modern traffic lights
Modern traffic lights are quite complex devices and consist of a traffic light itself with lamps, a traffic signal controller, as well as vehicle sensors. They are installed on special poles and supports at intersections and along highways.
A modern traffic light is controlled by a computer that selects and synchronizes traffic directions according to constantly changing traffic conditions. At the same time, motion sensors record vehicles moving along the highway, setting their driving rhythm with the help of light signals.
In large cities, traffic lights are combined into large automated traffic control systems that can create such rather complex effects as, for example, a “green wave”.
Further ways of developing a traffic light as a means of traffic control will lie in the field of artificial intelligence, which, over time, will be able to take over all the functions of regulating traffic flows, completely excluding a person from this process.
Why are the colors of the traffic lights the way they are? and got the best answer
Answer from Natalya Buldina (Mortisss)[guru]
Source: => Vita pulchra et necessaria. (lat.)
Answer from Iy[guru]
Some countries use orange instead of yellow. Signals can be placed both vertically (with the red signal always on top and green on the bottom) and horizontally (with the red signal always on the left and green on the right) . In the absence of other, special traffic lights, they regulate the movement of all types of vehicles and pedestrians. Sometimes traffic lights are supplemented with a special countdown display, which shows how long the signal will be on. Most often, the countdown board is made for a green traffic light, but in some cases, the board also displays the remaining time of the red signal.
Almost everywhere, a red traffic light signal prohibits movement, a yellow one prohibits leaving the area protected by a traffic light, but allows the completion of its passage, and a green one allows movement. It is common, but not universal, to use a combination of red and yellow signals to indicate that the green signal is about to turn on. Sometimes a green signal turns on immediately after a red one without an intermediate yellow, but not vice versa. The details of the use of signals differ depending on the traffic regulations adopted in a particular country.
There are two sections of traffic lights - red and green. Such traffic lights are usually installed at points where cars are allowed to pass on an individual basis, for example, at border crossings, at the entrance or exit from a parking lot, a protected area, etc.
Flashing signals may also be given, the meaning of which depends on local legislation. In Russia and in many European countries, a flashing green signal indicates an upcoming switch to yellow. Cars approaching a traffic light with a flashing green signal can take timely braking measures to avoid entering the intersection guarded by the traffic light or crossing the prohibitory signal. A flashing yellow signal requires you to slow down to pass an intersection or pedestrian crossing as unregulated (for example, at night, when regulation is not required due to low traffic) . Sometimes special traffic lights are used for these purposes, consisting of one flashing or alternately flashing two yellow sections.
Answer from Anastasia churilova[newbie]
Three colors are used in the light signaling of road transport - red, yellow and green.
For a person from time immemorial, it has developed that the color red is a signal of danger, alarm. It was fire that was always such a sign for him. Red has become a universally recognized hazard warning signal. And vice versa, the green signal has always been personified with safety, calmness, so it was natural to use it as a permissive traffic light signal.
Red rays have the longest wavelength and propagate with the least loss. Therefore, the red color is visible the farthest. The red signal is more visible and it is he who is accepted as a danger signal. This is especially important, for example, in low visibility conditions. For example, fog absorbs blue and green rays, so green in fog can be perceived as yellow, and yellow as red. If a driver in fog mistook yellow for red and green for yellow, then such errors would not pose a danger to traffic.
In the beginning, traffic lights had a green signal at the top, but then it was agreed that the red signal was more important for drivers and pedestrians and therefore it should be more visible. It is no coincidence that recently they even began to make lenses for this signal larger than the others.
