How do traffic signals develop?

With the appearance and development of automobiles, it is becoming more and more important for automobiles, people and other vehicles to drive scientifically, reasonably, safely and orderly on the road. In this process, traffic signals have developed. The original traffic controller was a foot patrolman. They use gestures to direct traffic. Then there were manual traffic lights. It was not until the early 1920s that automatic traffic lights came into use.

But there is still an important problem that cannot be solved, that is, the traffic flow at an intersection will change many times a day. 1927 two people obtained the patent of "flow-adjusting lamp" traffic control device. This device can adjust the traffic lights according to the traffic volume at the intersection at that time. One of the devices, invented by Professor Huo of Yale University, was first put into use in New Haven, Connecticut in April 1928. This device is controlled by a detector placed on the road and can feel the pressure. If a car runs over the detector, the electrode that controls the signal lamp will receive the signal immediately, and the signal lamp will give a green light to the oncoming car. We still use this traffic light today, but we have made some changes.

Also in 1928, Adler invented another kind of signal lamp. It uses a microphone to send out signals. When the driver stops at the red light and rings the car horn, the microphone will transmit the sound to the control signal light, and the red light will turn green immediately. Today, people also use some other voice-controlled dimming devices.