How traffic signals work

How traffic signals work

Discover the different mechanisms that make up traffic signals and how they work.

Image showing grid outlining a traffic detector at an intersectionDetectors

Traffic signals in Victoria have detectors in each lane at the stop-line of every intersection.

Detectors are wire loops located just under the road surface. You can see the outline of the rectangular loops at most intersections.

The detector loops work by sensing the metal in vehicles. This enables the system to know:

  • vehicles are waiting
  • how many vehicles are passing by
  • what movements need a green signal 
  • how long the green signal should be.

Example of a push button at a pedestrian crossing Push buttons

Push buttons are provided to allow pedestrians to request the green walk (green man) display. 

These are designed to be easy for all people to use. They produce a clicking sound and vibrate to help people with a disability to cross the road.

Image showing the inside of a traffic controller boxControllers

The brains behind each set of traffic signals live within the traffic signal controller box. 

This box houses the electrical switching and microprocessor control unit, and is located close to the intersection or pedestrian signals. 

Even if communications with the central computer (SCATS) are broken, the traffic signals will still operate under the control of the local controller.


image of traffic signalsPedestrian signals

Many pedestrian signals now have infra-red or microwave detectors facing the road where pedestrians cross. 

These modify the traffic signal timings to give more time to slower moving pedestrians and, if the pedestrians cross quickly, returns promptly to a green light for vehicles.

Learn more about pedestrian priority here


Studies have shown that installing traffic signals at a previous uncontrolled intersection can reduce crashes involving injury by 50% (Source: ‘Evaluation of the Effectiveness of the $240M Statewide Blackspot Program – Accident Blackspot Component’, RSD-0130, MUARC 2006).