How do Traffic Signals Work?

 How do Traffic Signals Work?

When you’re stuck at a red light, it can almost feel like traffic signals are designed to slow traffic down. But, in reality they’re always working to improve traffic flow. But how do they actually work?

Contrary to popular belief, most traffic signals aren’t set to arbitrary time schedules. Instead, five components send real-time information so that signals adapt to the traffic as it happens.

Central Computer

The most important component in a traffic light system is the central computer. This is the heart of the overall traffic control system. It receives information from all signals in an area, using the detectors, push buttons and pedestrian signals.

With this information, the central computer can adapt the length and changes of traffic signals in real time and improve the flow of traffic across a whole area, not just at a single intersection.

For instance, if traffic is moving slower because of poor visibility due to heavy rain, the central computer will extend the time between signal changes to allow for more vehicles to pass. On the other hand, during school holidays, it may reduce the time between signal changes because the system knows there are fewer cars on the road.

This adaptability to traffic conditions ensures that traffic flows as smoothly as possible through the routes with the most cars. So, while a back road might seem quicker, you might waste any time gained stuck at a red light when it comes time to rejoin the main road.

Traffic Control


Everyone knows how important it is to stop at a red light. But not everyone realises that where you stop plays a vital role in traffic flow. If you stop just behind the white line, you’re more likely to get a quicker change than if you stop a metre back or more. But why is this?

A detector sits under the road about half a metre back from the white line. This detector senses the metal in your car and sends a message to the central computer saying that someone is waiting for the lights to change.

If you aren’t quite close enough to the detector, it can take a while to register your vehicle. As a result, you may end up waiting at the lights longer than you need to.

Detectors also measure how many vehicles are passing through the intersection. This can help to adapt the signals to the real-time traffic flow by adjusting the light sequences to cater to peak or non-peak traffic loads.

Pedestrian Push Buttons

Push buttons at pedestrian crossings work like manual pedestrian versions of the vehicle detectors on the road. When a pedestrian wants to cross a road, they just need to push the button to send an alert to the central computer.

The pedestrian signals then gather data about the volume of pedestrians crossing. For instance, the signals will register if there are multiple pedestrians crossing as well as how fast they are moving.

The signals then send this information to the central computer so it can adapt traffic flow to cater to the pedestrian volume. This means that areas with a significant amount of foot traffic will have longer or more regular pedestrian cycles. This can sometimes slow down the flow of road traffic, but it ensures a smooth flow of pedestrians as well as the safety of the foot traffic.

Local Controller

The local controller also receives information from the detectors, push buttons and pedestrian signals, but only from those in the immediate area. Have a look on Why Do Roadworks Take so Long?

Generally, the central computer will manage the traffic, rather than the local controller. However, if the central computer loses connection with the traffic signals, the local controller will take over. As a result, traffic may not flow as smoothly in a wider area but traffic signals will still work.

While you can’t always guarantee a green light at every traffic signal, understanding how traffic signals work can help you reduce your waiting time. Remember to ensure your car is sensed by the detector and that traffic signals will always favour routes that are used by more vehicles.

Peter O'brien

Related post