We travel daily on roads and we also look at traffic lights which change colors after few seconds. Do you know how they change color and their working principle?

If you are an urban planner, traffic police officer or driver & you have a project related to traffic lights. Then this article is for you. We explain everything that you must understand related to the working of traffic lights. 

Traffic Light Working in 5 Steps

Traffic lights use a simple process to control traffic. Following are the main steps which help you to find how traffic lights work.

1. Vehicle and Pedestrian Detection

In the first step, traffic lights detect vehicles using sensors such as inductive loops, infrared sensors, radar or microwave sensors. These all sensors which are present under and above the road near traffic signals help to identify the vehicles.

Plus, they detect the pedestrian through a push button that you press to request a cross signal. Cameras which are present above the traffic lights are also used to monitor traffic flow, vehicle count, pedestrians and collect road data.

2. Signal Processing and Decision Making

The data gathered by sensors and cameras is sent to the controller near the traffic lights in a metal box. You can call it the brain of a system. The controller analyzes the information and then decides which traffic light should change next.

It also responds to emergency vehicles early and pedestrians when you press the pedestrian push button. In addition to this it makes sure that lights operate properly without any conflict signals to avoid accidents.

3. Signal Timing or Phase Control

In this step you will notice the timing of the signal which is carefully set by engineers or automatically. Each light stays on at a specific time for a specific duration to perform its function uniquely.

The duration of each light is based on congestion, intersection size and movement of traffic. Predetermined timing of each signal allows everyone to pass without too much wait. In case roads are very crowded, the timing of the green light may last longer to control the situation.

4. Traffic Signal Coordination

To make your travel more smooth, timing of various traffic signals nearby intersections are connected through a central traffic management controller. This actually happens on busy roads if you proceed at specific speed and encounter the next series of signals, that also has a green light.

You can call it the green wave or traffic signal coordination. It is not co-incidental but it is matched in such a way so that you prevent frequent stops, save your travel time and fuel. 

5. Traffic Light Change Colors

After coordination, the controller delivers a signal to the traffic light for changing colors. As you know traffic lights contain three basic colors which are green, yellow and red.

Green to Yellow Signal: When the green light stays on, it allows you to move forward. It remains on until all the vehicles cross safely. This light turns on for a specific time and then changes to yellow.

Yellow to Red Signal: It is a warning color and tells you to be prepared to stop. You must slow down your cars and bikes at this point because the yellow light switches to red soon.

Red to Green Signal: If you see a red light, you should completely stop your car or bike. So that other side vehicle passes without any risk of collision. The red light will shift to green in case the road is clear.

In this way, we can say that this cycle will continuously remain in the same operation.

Traffic Signal Algorithm

Below are some basic traffic control algorithms that traffic lights follow to manage the congestion.

Fixed Time Traffic Signal

These signals contain timers which are set in such a way to repeat the fixed cycle consistently. You will observe that they do not respond according to traffic movement. Red, yellow and green lights stay the same each cycle because they only follow preprogrammed sequences.

These signals work well for regular traffic intersections only. You can easily install it and also require low maintenance. But it doesn't have any camera or sensor and is not suitable for real time conditions. In fact, it still operates during roads are empty.

Actuated Traffic Signal

It uses sensors like an inductive loop which present the underlying layer of pavement to detect metals in vehicles when you drive over them. After detection, they adjust their timing based on the traffic volume. It also uses cameras to take input about vehicles or pedestrians and is ideal for real time demand.

The best advantage of actuated signals is that they allow for smooth flow of traffic and reduce delays. However, these are more expensive than fixed time signals and require ongoing maintenance.

Adaptive Traffic Lights

Adaptive traffic control signals are the most advanced systems. It contains artificial intelligence, networks of sensors, cameras and processors to gather the data across multiple intersections. After that, the data such as traffic patterns and congestion are analyzed locally or centrally to adjust the timing of traffic lights. You will see that they modify the signal using an algorithm.

If we talk about its benefits, then it reduces accidents, maximizes efficiency and safety by maintaining balance. In addition to this, its initial cost is very high and installation is also complex for you. You must have a central traffic control system and a skilled operator for it.

4 Types of Traffic Signals You Need To Know

Vehicle Traffic Signals

Motor vehicle traffic signals usually consist of three circular face lights. It guides you about traffic rules. You can safely travel on the road by following these instructions. These three well-known lights and its time duration are:

Green: It means you have permission to go. This actually lasts almost 7 seconds to 2 minutes.

Yellow: This light gives you warning to slow your vehicle speed. The minimum time it stays on is approximately 3 to 5 seconds. 

Red: If you notice a red light you have to stop fully. The duration of this light is up to 10 seconds.

Pedestrian Traffic lights

If you want to cross the road by foot, first of all you should activate the pedestrian button. So that you can proceed without collision. It contains different color icons based on different countries.

For example, white or green person walking on it means you can move, flashing orange or red hands tell you not to start crossing but to finish if you're already in the street. Furthermore, a steady orange or red hand also signifies you stop and do not start.

Arrow Traffic Signal

Arrows traffic signals guide you in different directions. It allows you to go only where arrows point. You must obey them for your specific lane. It is similar in color to vehicle traffic signals. They guide when you should turn or go straight. Green arrow means you can pass in the direction of the arrow, yellow arrow tells it to turn to red soon and as result you are ready to stop. 

Moreover, flashing yellow indicates you need to yield oncoming vehicles and pedestrians. While the red arrow points to you, wait and stop totally for a few seconds until the signal shifts into green.

Countdown Traffic Signals

It displays you the remaining seconds left to modify the signal. As a result drivers turn off their engines for a while and plan their movement when they look at the timers. You will observe these signals commonly on busy roads. Red light timers show you the exact time left to turn green and green into red. Whereas pedestrian timers indicate seconds remain to finish the crossing.

In this way, it reduces the stress, fuel consumption (5%to10%) and allows pedestrians to have enough time to pass carefully. But some drivers speed up to beat the changing green light which can cause crashes.

Importance of Traffic Light

After knowing the working of traffic lights, you should also know its importance.

• Traffic lights reduce accidents by stopping vehicles at red lights so that pedestrians pass crossing harmlessly. 

• You will notice these organize the traffic by allowing one side to go and other sides to retain.

• It tells you clear rules where you should move or what to do and also fastly response to emergency vehicles.

• Smart traffic lights save your time, minimize the traffic jam and make your journey smooth.

• They also reduce pollution such as carbon emission and save your vehicle fuel.

Can Traffic Lights Be Controlled Remotely?

Yes, traffic lights can be controlled remotely. You can (city workers) use Advance Traffic Management System (ATMS) software from the office to monitor the data feed by camera and change light time.

Road engineers use internet links such as VPN, cellular data and industrial routers to fix and update signals from far away. You can also use handheld wireless (5G and Wi Fi) remote within short range to modify the signal especially during emergencies. 

If we tell you about most traffic control lights, it integrates an AI algorithm to analyze the information and real time adjustment of traffic signals. But you keep in mind that it requires strong cybersecurity to prevent the hackers from breaking the system.

Smart Traffic Lights vs Traditional Traffic Lights

Do Traffic Lights Have Sensors For Emergency Vehicles

Definitely, traffic lights have sensors for emergency vehicles. These systems use a technology which you can call traffic signal preemption. Suppose ambulance, fire trucks and police approach to signal it changes into a green light within seconds. It is because it sends radio signals, infrared light and GPS system that is detected by sensors present on traffic lights such as white detectors. 

As a result, you can reach your specific location during a crisis situation without any delay. After passing the rescue vehicle, the controller transitions back to its normal cycle. Moreover, you can observe this system on busy junctions only.

People Also Ask

What Should You Do When Traffic Lights are Out of Order?

If traffic lights are completely broken or dead, you must stop completely. You should treat the junction as an all-way stop sign or unmarked cross road. You must yield to vehicles which arrive first or on your right and also look around at the people crossing on the road. You need to proceed carefully and must report to local police and city council so that they can fix them.

Do All Countries Use the Same Traffic Lights?

No, all countries do not use the exact same traffic light. Most of the nation uses standard red, amber and green but others differ in light sequence, physical layout and unique local rules.

For example, Japan uses deep blue for go, UK and Germany show the red and yellow light before green light. Whereas most Europeans use blinking green light to warn the driver about the signal turning to yellow.

Why Are Traffic Lights Called Robots?

In South Africa and Neighbourhood countries such as Namibia called them robots. Because automated electronic signals replaced the first human traffic police late in 1920s and 1930s. People viewed these mechanical replacements as automated workers and referred to them as robotic traffic controllers. After this term, modify it into robot words.

Are traffic lights powered by AI?

No traffic lights are not powered by AI. However, modern intersections use AI as sensors, radars and cameras. They collect the data about road conditions and analyze it to adjust the timing of traffic signals.

What countries don't use traffic lights?

Bhutan is a famous country in the world which has no traffic lights. Trained police officers stand to control the traffic at busy intersections. If we go back in the past, a traffic light was installed in Thimphu in the 1990s but it was quickly removed because local residents complained and think it is too modern. They preferred the traffic officers only.

What overrides a traffic signal?

A traffic signal overridden by police officers and authorized officials through hand signals and direct command. In addition, as you know, the emergency vehicle preemption system also overrides traffic signals. Whereas city transportation authorities can manually or remotely modify the signal timing from the central monitoring system to control congestion.

Final Thoughts

After the above discussion, we hope now you have detailed knowledge about working of traffic lights. You can see its components such as sensors and timers each of which perform their job in a unique way. So, whenever you observe traffic light, you must give proper attention to it and follow Govt rules.

Furthermore, if you want to purchase traffic light for your project, JACKWIN is a professional manufacturing partner for you. You can contact our team to get customized products according to your requirement.

More helpful resources:

Recent development of smart traffic lights

Traffic Calming Measures and 24 Traffic Calming Devices

ELI5: Traffic lights and emergency vehicles : r/explainlikeimfive

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