How Traffic Light Control Systems Work

Traffic lights, the one thing on the road that most drivers hate 6 photos
Photo: Audi
Traffic light controllers determine the number of vehicles on the roadAudi's system allows the vehicle to communicate with traffic control systemsAudi's system allows the vehicle to communicate with traffic control systemsAudi's system allows the vehicle to communicate with traffic control systemsAudi's system allows the vehicle to communicate with traffic control systems
Both car manufacturers and state authorities have been struggling to boost vehicle efficiency and improve the safety of passengers and pedestrians for several years already. While the automotive industry has evolved at a very fast pace in the last decades and new safety and greener systems eventually got to see daylight, the most efficient way to tackle these two particular areas seem to come down to a different concept: traffic lights.
We've all seen and heard of them, and chances are that most drivers hate them from the depths of their souls. They block them from reaching their destination faster, they increase fuel consumption, and, sometimes, they force everybody to waste minutes after minutes simply sitting and waiting for the green light.

But despite these massive shortcomings, traffic lights play an essential role in the complex world that traffic has become. They are the ones responsible for making everything safer, not only for drivers, but also for pedestrians.

Everybody knows how traditional traffic lights look and what they come down to, but the world of technology and the way it expanded into the automotive industry helped evolve this concept in a substantial way. This is why we now have smarter traffic light systems that provide even more advanced capabilities, including adaptive traffic management to help tackle traffic jams and slowdowns.

In many ways, these smart traffic light control systems are fascinating technology, and understanding how they work isn’t necessarily easy, especially for people who aren’t tech-savvy. So fasten your seatbelt and let’s discover the magic that lies underneath their cases and the spell that makes them turn green when a car approaches.

Although in some regions authorities and various companies have started testing innovative traffic light control systems, there are usually two different modes adopted by most nations on the planet: fixed-time units and dynamic control. Let's take them one at a time and see the differences.

A fixed-time traffic light control system is that boring and old-fashioned way in which traffic lights are configured to turn on the green color after a given time, usually around 30 seconds. However, as we all learned the hard way, this may very well vary depending on traffic values and region.

We won't get too technical and dissect every single part of such a system, but it's worth mentioning that fixed-time traffic light control systems typically rely on what it's being called an electro-mechanical signal controller. In plain English, it's a basic controller with components that can move (hence the “mechanical” term), but also with dial timers to be able to keep a specific color for a defined time.

Dynamic traffic light control systems, on the other hand, are more prepared to handle the crowded traffic we're facing every morning, as they have been developed specifically to be able to adapt their settings to real-time traffic conditions. In case you're driving at rush hour and seeing green all the way from the office to home, you're in luck: dynamic signals have turned all traffic lights to green to maintain traffic flow.

Traffic light controllers determine the number of vehicles on the road
Photo: ATC
As compared to fixed time control systems, the foundation of a dynamic system is actually a detector, which is nothing more than a simple device that communicates with the traffic light and informs it about traffic conditions in real time. This time, the traffic light can not only adjust timing but also solve traffic jams by turning red as soon as an intersection gets filled with cars.

There are two different types of detectors: embedded into the road surface and installed above the road.

The first ones are nothing more than simple devices that use an inductive loop, so they have the ability to send information to the traffic light unit when a car passes over it. This way, the traffic light, which already has the power to control timing all by itself, knows for sure whether there's a queue of cars waiting for the green light or there are no vehicles at all, thus acting accordingly. Or simply said, if a car is on the road, the traffic light is fully aware of it.

If you’re an experienced driver, you probably noticed such a detector already. This is because their design isn’t necessarily subtle, as such technology requires small holes that must be drilled right into the surface of the road. These systems are typically installed near intersections or close to crosswalks, and, in some cases, they are marked accordingly.

While they’re fairly common in some parts of the world, inductive detector loops come with one big drawback: they are more expensive than all the other alternative systems, so authorities out there are already developing new strategies to switch to smarter technology. The installation cost of an inductive detector loop is typically ridiculous, while the maintenance cost, especially given they are embedded into the road directly, doesn’t make much sense in the long term.

The detectors that you typically see on poles, right above the road, come with significant benefits. And without a doubt, the first of them is the cost. Such a system is a lot more affordable, not only to install, but also to service in the long term. Its design allows the installation in close proximity to other systems.

Audi's system allows the vehicle to communicate with traffic control systems
Photo: Audi
The feature that most authorities are looking for when picking such a system, however, comes down to the information that it collects and transmits to a receiver. For example, this type of detector is able not only to determine how many vehicles are on the road at a given time (as it’s even capable of counting them), but also to transmit other types of data, such as real-time photos.

While all these systems are being used right now in many regions around the world, there's one city in Germany that makes us believe the future sounds good. Ingolstadt, home of German car manufacturer Audi, has long been testing what's being considered the first intelligent traffic light system in the world.

This new-generation concept, however, is based on a completely different approach whose main engine is the communication between the car and the traffic light. In other words, the traffic lights can directly connect to nearby vehicles and exchange essential information, so the system no longer requires detectors and sensors installed on the surface of the road.

While such a design is a brilliant way to handle heavy traffic, Audi’s original idea was supposed to demonstrate that traffic lights are a key component of the fuel-saving push. By allowing vehicles and traffic lights to exchange data, fuel consumption could eventually be reduced by optimizing the speed and reducing the time spent waiting for the green light.

The whole idea is pretty simple: the vehicles communicate with the traffic lights via special equipment, mostly wireless LAN and UMTS links. Traffic lights send various information to the approaching car, including the time until the next color change, so the vehicle can either automatically adjust speed to avoid stopping or inform the driver about their options.

The permanent connection between the traffic light and the vehicle produces significant benefits on both sides. Whenever a vehicle is stopped at a traffic light and waiting for the green light, the onboard computer communicates with the traffic control system and requests essential information, such as how long it takes until the light changes. In exchange, the vehicle sends the waiting time, thus allowing the traffic control system to optimize the nearby traffic lights accordingly. We’ve already discussed the travolution project in detail, so you might find this new system quite fascinating.

That being said, it's pretty clear that traffic light systems are playing an essential role in the automotive industry, and although we all hate them when they turn red, don't be too harsh on them. They're here to make public roads a better place.
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About the author: Bogdan Popa
Bogdan Popa profile photo

Bogdan keeps an eye on how technology is taking over the car world. His long-term goals are buying an 18-wheeler because he needs more space for his kid’s toys, and convincing Google and Apple that Android Auto and CarPlay deserve at least as much attention as their phones.
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