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How Does a Traffic Light System Work?

Posted on by Judy Johnson

Traffic light systems are integral parts of road infrastructure because they keep drivers and pedestrians safe while efficiently regulating the flow of traffic. These systems can operate either through fixed timers or sensor activation. Here we’ll discuss the components and nuances of these systems, as well as different product options to customize your traffic light system for your local traffic demands.

Traffic Light System Components

Every traffic light system is made of three main components: the signal head, controller, and detectors. The red, yellow, and green lights of a signal head indicate how drivers should approach an intersection. Red indicates stop, green indicates go, and yellow indicates the driver should either prepare to stop or accelerate to clear the intersection before the light turns red. Detectors provide information about real-time traffic conditions, and the controller uses this information to change the lights.

How Does Traffic Light System Work

Types of Traffic Light Systems

Traffic lights are regulated either by timers or sensors, reflecting the two main types of traffic light systems. Each one is better suited for different types of intersections.


Fixed-time traffic lights display red and green lights for fixed periods of time for every direction of traffic, regardless of traffic conditions. Once the set time elapses, the controller initiates the lights’ transition from red to green or green to yellow to red. This system is best for intersections with consistent, high-volume traffic in all directions, such as busy city streets.

Timer-based systems are the most common type of traffic light system. However, at intersections where traffic is variable, fixed-time traffic lights are not efficient. For example, a timer-based traffic light at an intersection between a major boulevard and a small avenue would often make drivers along the main road stop unnecessarily. Intersections in rural areas with sparse or unpredictable traffic flows also may not benefit from fixed-time systems.


Sensor or vehicle actuated systems depend on detectors embedded under the road or in the traffic light heads. Under the road, an inductive coil detects when there is a change in the magnetic field, such as when vehicles stop above it. Sensors embedded in the signal head work similarly, except they utilize lasers or cameras to detect vehicles. Both types of sensors send a signal to the controller to change the traffic lights accordingly.

Sensor-activated systems often supplement timer technology by picking up traffic demands in real-time and helping the controller regulate how long green lights should last in each direction. Some sensor-based systems are also advanced enough to change depending on the approach of emergency vehicles like fire trucks, ambulances, and police cars.

Because sensor-activated systems are more flexible, they are better suited for intersections with fluctuating traffic levels, such as those in rural or suburban areas.

Types of Timers

Interval Timer

At Amperite, we carry a vast selection of timers for traffic lights, vehicles, commercial dryers, sprinklers, elevator doors, and more. Here are our most common timer products for traffic light systems.

  • Programmable Recycling Timer
  • Flashers
  • Interval-Type Timer

Traffic Light Timers From Amperite

HDFA Recyclable Timer

Understanding how traffic light systems work helps determine which type is best for a given intersection. In general, those with consistent, high-volume traffic should use timer-based systems, while those with varying traffic levels should use smart sensor systems. Every intersection is different, so consult with an expert in traffic light technology before making your selection.

At Amperite, we specialize in manufacturing controlling devices, flashers, and time delay relays for OEMs, including traffic light providers. Our custom-made products ensure that you receive a high-quality solution for your specific needs. To find out more about our products and capabilities, contact us today.

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