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What’s in the Box?


Just kidding – no robots in the boxes.

Have you ever wondered what’s in those big metal boxes on street corners? Some may be painted and some may be plain aluminum –  but what goes on inside those things?

If you happen to be at an intersection with a traffic signal, what you’re looking at is a signal controller cabinet.  These cabinets control the traffic signal and house all the sensitive electronic equipment that help the signal work efficiently.

What’s in the box?

  • Signal controller: The brains! These devices are simple computers that receive inputs from various sources that, along with a timing plan, make decisions on how to change the signal.


    Signal controller. Photo courtesy of Siemens.

  • Detection: The eyes and ears. Our traffic signals use one of three types of detection methods (video, inductive loop and magnetometers) to notify the signal that there is a vehicle, bicycle or pedestrian at the intersection, allowing the controller to provide each their turn in the intersection.

Three types of detection methods: video, inductive loop and magnetometer.

  • Priority Devices: Decision-making part of the brain. These detect when an ambulance or fire truck is coming and make sure that they have quick and safe passage.
  • Communication equipment: The mouth! Traffic signals communicate with each other through a copper wire system or fiber optic system similar to high speed internet systems.

All these parts work together to keep a signal operating reliably. Now you know what’s in the box!