Road traffic signals are made up of red lights, green lights and yellow lights. A red light means a ban, a green light is allowed and a yellow light is a warning.

Road traffic signals are divided into: light motor vehicles, non-motor vehicles lights, pedestrian signal lights, direction indicator lamp (arrow lights), driveway lights, flashing warning lights, road and rail light plane crossing.

At the crossroads, red, yellow, green, and tri-colored traffic lights were hung on all sides, and it was the silent "traffic policeman". The traffic light is the international uniform road traffic light. The red light is the stop signal and the green light is the signal. At the intersection, the cars that come in several directions are gathered here, some to go straight, some to turn, who to walk first, which is to obey the traffic light. Red light, no direct or left turn, in the case of pedestrians and vehicles, allow the right turn of the vehicle; Green light to allow the vehicle to go straight or turn; Yellow light, more than stop line or pedestrian crossing line, can continue to pass; When the yellow light flashes, alert the vehicle to safety.

According to the principle of optics, the wavelength of red light is very long, penetrating air capability is strong, and more attention than other signals, signals, as no thoroughfare by using green as announcement signals, because of the difference between red and green is the most big, easy to distinguish (red green color blindness is minority after all). In addition, color can also express some specific meaning, to express hot or intense words, the strongest is red, followed by yellow. Green has a cold and calm meaning. Therefore, people often represent danger in red, yellow stands for warning, green is safe

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