How Does Traffic Light Work?

It is boring to be stuck with a big flashy red signal. Although traffic lights might not be the most attractive thing during a road trip, it helps drivers to communicate. Imagine if cars whooshed past with zero control at crossroads, with no traffic signal to guide them on when to go and when to stop. That would be a recipe for accidents, right? Traffic lights also signal when a pedestrian should cross a street.

What does each color mean?

A traffic light has three colors— red, yellow, and green. Each color instructs the drivers— whether they should go or stop at the signal.

When the light turns red, it’s time for everyone to stop. This is crucial to prevent accidents and give others a chance to safely cross the road or make their turn. The color red is used because it scatters less. When a ray of light travels in the air, it bounces off from one particle of dust to another. Light disperses in this manner, a process called scattering . Scattering can make a light appear less bright when far. Therefore, scattered light is not much visible the farther we go, something that doesn’t sit right with the purpose of traffic lights. Red light scatters the least and hence makes for an excellent signal visible far off on the road.

When the light turns green, it’s the signal to go. Vehicles and pedestrians can proceed safely through the intersection.

Yellow or amber suggests that the cars either need to stop at the signal soon or the vehicles will be released soon— the signal will turn green.

Modern traffic lights are computerized and have a control box nearby. Traffic lights might also be remotely controlled. The computerized system of traffic lights controls the timing of the lights. Data of the usual traffic is fed into the computer, and the lights cycle through the red, yellow, and green colors at certain time intervals. Timers are great options on busy roads with consistent traffic.

The traffic light’s computer uses sensors to determine when to change the lights. These sensors detect the presence of vehicles waiting at the intersection or pedestrians pushing the crosswalk button. Based on this information, the traffic light’s brain decides how long each color should stay lit. Video cameras, lasers, and wires that detect changes in magnetic fields are mainly used as sensors.

The magnetic system uses wires embedded in the road that detect any change in the magnetic field when a large metal object stops above it, such as a car. This system is called the inductive loop system and is fairly new.

Sometimes, emergency services like ambulances, fire trucks, etc., can change the traffic signal at intersections from their vehicles. This is called the traffic pre-emption system and minimizes emergency vehicles from getting stuck in signals.

Traffic signals have variable timers

During busy times, like rush hour, the green light may stay on longer for the main road to keep traffic moving smoothly. Similarly, at night when there’s less traffic, the lights might change faster to prevent unnecessary waiting. The traffic patterns are not fixed throughout the day, so the traffic lights get some breathing space when the traffic is less.

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Glossary

Scattering: The process by which light is dispersed as it travels through a medium, such as air, due to interactions with particles, like dust. This phenomenon causes light to appear less bright as it travels farther.

Sensors: Devices that detect and respond to changes in their environment, providing information to a system for appropriate actions.

Magnetic Fields: The area around a magnet where its influence can be felt. Sensors can detect changes in magnetic fields.

Inductive Loop System: A technology that uses wires embedded in the road to detect changes in the magnetic field caused by large metal objects, like cars, passing over them.

Traffic Pre-emption System: A system that allows emergency service vehicles, like ambulances and fire trucks, to change traffic signals at intersections to prioritize their passage.